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Ethnicity and Cut-Off Values in Obesity
C H A P T E R
17 Ethnicity and Cut-Off Values in Obesity Ejiroghene Martha Umuerri Department of Medicine, Delta State University, Abraka, Nigeria
O U T L I N E Introduction
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Waist-Hip Ratio
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Ethnicity and Perception of Obesity
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Waist Circumference
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Waist-to-Height Ratio
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Definition and Measurement of Obesity: Historical Perspective 212 Cut-Off Values for BMI
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Ethnicity and Central Obesity Cut-Off Values
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Ethnic-Specific BMI Cut-Off Values
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References
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Cut-Off Values for Abdominal Obesity 217
INTRODUCTION The human body composition made up of fat mass and fat-free masses (blood, bone, skeletal muscles, visceral organs) accounts for variations in the human body frame. Human variations in body size and habitus are age-long. Genetic, social, cultural, environmental, and economic factors have influenced the diverse phenotypic expression of body size in humans. Persons with large body size have existed throughout human history. One of the contributory factors to large body size is an excess accumulation of fat. The fat mass and “fat-free” masses differ not only with age and sex but also with ethnicity.1,2 Although difficult to define, ethnicity usually refers to a group of people identified by shared similarities in their sociocultural values, beliefs, and practices. For example, people of the same ethnic group share similar genetic characteristics as well as lifestyles such as food choices, occupation, and recreational
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activities. Hence, similarities in body size and shape among people of the same ethnicity are not surprising. This chapter shall focus on ethnicity and obesity cut-off values among adults.
ETHNICITY AND PERCEPTION OF OBESITY Obesity refers to the condition in which there is an excess accumulation of fat mass. The prevalence of obesity has been noted to increase in the past three decades significantly. In a considerable part of human history, large body size has been associated with status, affluence, beauty, and sometimes good health. Indeed, prehistoric statuettes of abdominally obese women such as the Venus of Willendorf and other Venus figurines were not uncommon and were thought to portray success and fertility. It used to be an acceptable cultural practice among some ethnic groups in West Africa for young girls to be kept in the fattening room to make them plump and beautiful. For example, among the Annang people of Nigeria, young ladies were held and nurtured for a variable period in their father’s compound until they are big enough as part of the cultural practices before marriage.3 Women who are fat were perceived to be more fertile and adequately nourished to breastfeed their babies for up to 2 years. This custom was not only as part of preparations for a successful reproductive career after marriage but also a prerequisite to being initiated into the prestigious secret cult of married women. The perception of body size still varies somewhat with ethnicity. Positive cultural values for large body size hold sway in some ethnic groups around the world especially in subSaharan Africa and the Pacific Islands.4,5 Men who are big are often well respected as they are perceived to be wealthy. Women with full-bodied habitus are viewed as attractive and well-cared for in some cultures. In a study in the United States, black and Hispanic men preferred women who are fat compared to white and Asian men.6 Culture is however evolving. In westernized cultures as seen in many developed and some developing countries, a negative perception of obesity is favored, especially among young people. This opinion is not necessarily for health reasons. Persons with slender built are perceived to be trendy. The mass media has helped in no small way to influence this mindset.7,8
DEFINITION AND MEASUREMENT OF OBESITY: HISTORICAL PERSPECTIVE The concept of obesity and its relationship with health status is not entirely contemporary but dates back to the Hippocrates era. Obesity, akin to large body size, was linked with infertility and premature deaths.9 About 250 years ago, the link between obesity and disease was reaffirmed by the independent works of George Cheyne MD (1671–1743), a renowned physician and Joannes Baptista Morgagni (1698–1771), the legendary Italian physician cum anatomist.10,11 Cheyne, who himself suffered from obesity, attested firsthand to the adverse health consequences of obesity including depression and nervous disorders.12 In particular, Morgagni noted the link between the distribution of body fat and diseases such as hypertension, hyperuricemia, and atherosclerosis. He reported visceral fat in the abdomen and
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mediastinum as the culprit.11 In the mid-20th century, Jean Vague, a French physician and Professor at the University of Marseille, documented observed differences in metabolic complications associated with regional fat distribution.13 He noted that upper body fat centered around the abdomen, which he named android obesity, was a risk factor for cardiometabolic diseases. On the hand, lower body fat distributed around the hips, gynoid obesity was not associated with adverse metabolic consequences. Since then, several other researchers have linked abdominal obesity with more adverse health outcomes compared with general obesity. Although obesity cannot be considered a disease in its entirety, the link between excess body fat and its regional distribution and health challenges is not in contention and preventive measures put in place.14 The definition of obesity has however evolved. Several efforts have been made to define ideal body size as well as one with an increased propensity to medical conditions. About 25 centuries ago, in the Hippocrates era, obesity was defined as having excess “humors” or body fluids, that is phlegm, yellow bile, black bile, and blood.15 In an attempt to define an ideal or average body weight, Lambert Adolphe Quetelet (1796–1874), a Belgian mathematician and statistician conducted a study in the mid-19th century that revealed that the increase in weight of an individual was a function of the square of the individual’s height. His work led to the formation of a table of average body weight for Belgian adults.15 Quetelet’s intent, however, was not to define obesity or excess body fat and his proposed anthropometric index, defined as a ratio of the body weight to the square of the height, was not utilized for this purpose until several decades later. Actuarial tables were references put together by the life insurance industry to obtain ideal body weight. Data derived from observed sex-specific weight-for-height associated with minimal mortality were used to compute these tables.16 These actuarial tables were not without flaws. Before the 1970s, body weight in proportion to height in diverse functions was used as an anthropometric indice and surrogate to measure body fat, even though none of the indices then was considered universally as the benchmark.15,17,18 In a quest to find the anthropometric index that will best indicate fatness or obesity among the existing indices, Professor Ancel Benjamin Keys (1904–2004), an American physiologist at the University of Minnesota, led a large comparative multinational study.17 In this study, over 7000 apparently healthy men from 5 countries were recruited across the globe—United States of America, South Africa, Japan, Italy, and Finland. The height and weight of lightly clothed and barefooted participants were measured and anthropometric indices calculated—weight-to-height (W/H), weight-to-squared height (W/H2), and weight-to-cubed height (W/H3) (the ponderal index). Body fatness was measured using body density obtained via underwater weighing, a relatively hard and time-consuming procedure, and skin-fold thickness at specific sites. The calculated anthropometric indices were compared to ascertain which one best correlated with body fatness. Although the study participants were not fully representative of the general population, the weight-to-squared height (W/H2), which is the same as Quetelet’s index, stood out as the best index. Keys and colleagues published their findings in 1972 and renamed this anthropometric index as the body mass index (BMI).17 Since the 1980s, the United States National Institutes of Health (NIH) have advocated and popularized the use of the BMI as a means of assessing body fat. Although the landmark study by Keys et al. did not include women and was for use at population levels, BMI is used to assess adiposity in both men and women, and across different age groups at individual and population levels.19 Till date, the BMI, a cheap and quick
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method of assessing adiposity, is the most widely used anthropometric index to define obesity for clinical and epidemiological purposes. In addition to anthropometric indices derived from weight and height, waist and hip circumferences were used to obtain the waist-hip ratio (WHR), an anthropometric index of abdominal adiposity.20 The World Health Organization (WHO) recommends that the waist circumference (WC) is measured at the mid-point between the lower border of the ribcage and the top of the iliac crest while measurement for the hip circumference is at the fullest part of the buttocks, usually around the greater trochanter.20 In two separate longitudinal studies in Sweden, Larsson et al.21 and Lapidus et al.22 showed that WHR was an independent risk factor for obesity-related cardiometabolic mortality and morbidity among men and women, respectively, indeed reaffirming the integrity of the earlier submissions by Morgagni11 and Vague13 on the significance of regional fat distributions and its strong correlation with adverse cardiovascular events.11 In addition to the WHR, other anthropometric indices have been validated to assess abdominal obesity. These include the WC, waist-to-height ratio (WHtR), the waist-to-thigh ratio (WTR), sagittal abdominal diameter, and the abdominal diameter index (sagittal abdominal diameter to mid-thigh girth ratio). The WC is easy to measure and interpret and correlates well with visceral fat. Like the WHR, the WTR helps to differentiate upper body (android) obesity from the lower body (gynoid) obesity, although its predictive values are higher than WHR. Several studies have shown that abdominal obesity has a stronger predictive value for adverse cardiovascular outcomes like stroke and coronary artery disease and death than general obesity measured by BMI.23–27 In the assessment of generalized and central obesity, there were remarkable technological advances in the 20th century.28–30 These include the use of computerized tomography (CT), magnetic resonance imaging (MRI), and dual-energy X-ray absorptiometry (DEXA) to estimate percentage body fat as well as regional fat distribution. Unlike anthropometry, these methods are costly, time-consuming and require high-level expertise in the procedure and interpretation thus, limiting their routine use at both individual and population levels.
CUT-OFF VALUES FOR BMI The WHO defines obesity as a medical condition in which excess accumulation of body fat results in adverse health outcomes.31 Obesity and numerous multi-systemic health conditions are linked. These include dermatologic, musculoskeletal, neuropsychiatric, respiratory, and cardiometabolic disorders such as hypertension, diabetes, stroke, and coronary heart disease, as well as specific cancers. The direct economic and social costs of obesity are enormous. Unfortunately, with globalization and the increasing adoption of lifestyles that favor a positive energy balance (energy intake more than energy expenditure), the prevalence of obesity has attained a pandemic proportion. Likewise, the incidence of type 2 diabetes is escalating globally. This concurrence calls for urgent action. The need for an appropriate anthropometric indicator and optimum cut-off value for BMI led to the constitution of a WHO Expert Committee on Physical Status with over one hundred experts in 1991.32 Following evaluation of series of scientific research and reviews, the WHO in 1995 published a technical report of the Expert Committee. Anthropometric indicators were chosen based on the identification of “at
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ETHNIC-SPECIFIC BMI CUT-OFF VALUES
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risk” individuals or populations, prediction on benefits of interventions at individual and population levels, assessment of response to interventions, and normative reference. Another WHO Expert Consultation met in 1997, and healthy weight-for-height was put at a BMI of 18.5–24.9 kg/m2 while 25 and 30 kg/m2 were recommended as the BMI cut-off values for overweight and obesity in adults Caucasians, respectively.33 Although the BMI cut-off values were approved based on observed obesity-related mortality and morbidity rates, they were just appropriate for identifying increased adiposity and not as targets for interventions in isolation. Until recently, the WHO BMI cut-off values were applied globally without recourse to ethnic differences.
ETHNIC-SPECIFIC BMI CUT-OFF VALUES Ethnic differences in body composition have been demonstrated using dual-energy X-ray absorptiometry (DEXA). Using the DEXA method to access body composition, black women have been shown to have a higher bone and muscle mass, and a lower fat mass compared to white and Hispanic women at the same BMI levels.34,35 Asians compared with Caucasians, African-Americans, and Pacific Islanders have smaller body frames and thus lower BMIs. For instance, assuming the WHO BMI cut-off values for overweight and obesity were equated to percentage body fat, it pre-supposes that the cardiovascular and metabolic risks associated with obesity will be least among Asians. On the contrary, these risks are higher among Asians compared to other ethnic groups, disproving the veracity of this assumption. Several studies have shown ethnic variations between the WHO BMI cut-off values and percentage body fat, and the observed obesity-related cardiometabolic outcomes.36–47 Although Asians have a lower BMI compared with other ethnic groups, their percentage body fat is paradoxically higher for the same BMI. Deurenberg et al.40 in their review of the available literature showed that for a given BMI, Asians had a 3%–5% point higher percentage body fat compared to Caucasians. Conversely, for a given percentage body fat, Asians had a 3–4 unit lower BMI. In a 20-year prospective study (1980–2000) of over 78,000 apparently healthy women,42 although gaining weight was associated with increased risk of developing type 2 diabetes, the risk was highest among Asians. Observations from this study revealed that at the same BMI, the risk of developing type 2 diabetes among Asians was significantly higher than that of the Caucasians. Similarly, blacks and Hispanics in this study had a higher risk of developing type 2 diabetes compared with Caucasians, but less than the Asians.42 Davis and colleagues also demonstrated the higher propensity of Asians to develop hypertension and hyperlipidemia compared to their counterpart Pacific Islanders and Caucasians with similar BMI.45 In another longitudinal study of over 36,000 adults, the all-cause mortality from obesity at any given BMI above 25 kg/m2 was higher among Asians compared to Caucasians.46 Equating BMI with percentage body fat across different ethnic populations may have far-reaching implications that can be detrimental to overall public health in some populations. The ethnic differences in obesity-related outcomes are not surprising as the percentage body fat, rather than BMI, is the critical factor in defining adiposity. Therefore, the appropriateness of using a generic BMI cut-off value as a surrogate of adiposity irrespective of ethnicity begs for review. Proponents of this view have called on the WHO and other international organizations to review and recommend ethnic-specific BMI cut-off values for obesity.48,49
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In 2002, a WHO expert consultation meeting examined and agreed with available scientific evidence supporting the paradoxical low BMI and high percentage body fat, and the higher cardiometabolic risks of Asians compared to Caucasians.50 Aside from inter-ethnic differences in fat mass, there are differences even within the same ethnic groups.40 For example, in a study of apparently healthy adults of European, Chinese, and South Asian origin, BMI was compared with percentage body fat derived using DEXA.51 At any given BMI, the percentage body fat of the Chinese and the European participants was similar whereas it was 3.9% higher among the South Asians.51 However, in other studies, Chinese were reported to have higher percentage body fat at any BMI compared with Europeans.36,37,52 Also, compared with Caucasians, Chinese and other East Asians have a higher prevalence of obesity-related cardiometabolic risk factors, particularly type 2 diabetes.52,53 The need for ethnic-specific BMI cut-off values is however not without controversies. There are a few opponents to the position that the WHO BMI cut-off values33 should give way to new ethnic-specific BMI values. One of such opponents is Professor June Stevens.54–56 In her opinion, the call for ethnic-specific BMI values needs to be viewed carefully without prejudice to any political undertone. She hinged her arguments against ethnic-specific BMI cut-off values on three points.57 First, obesity cut-off points are arbitrary numbers that should be based on risk rather than percentage body fat. Furthermore, when making comparisons between and within ethnic groups care must be taken to match study designs and measures used to identify risks.46,57 If the needed scientific thoroughness is not applied, there may be significant flaws in inferences made. Second, she opined that there are not enough data to support a higher mortality rate among Asians compared with Caucasians at BMI >25 kg/m2.56,57 Lastly, to single out ethnicity as the basis for redefining obesity cut-off will be a hard task to substantiate socially, environmentally, and politically, particularly as other factors influence variations in BMI.57 However, she supports the call for different nations to set BMI thresholds for public health intervention as deemed applicable. In spite of affirming evidence from existing data, the WHO Expert Consultation did not recommend a new BMI cut-off value for Asians because of the inherent complexities.50 Instead, in their report, they made a distinction between the use of BMI cut-off for defining obesity as a disease and the use of the cut-off values as action points. The WHO Expert Consultation group recognized the BMI as a continuous variable and therefore recommended targets for public health interventions instead. Among Asians, putting the total cardiovascular and metabolic risks together, the recommended BMI cut-off values for initiating interventions for “increased risk” and “high risk” are 23 and 25 kg/m2, respectively.50 Nationalities were encouraged to develop their country-specific cut-off values. In 2009, the Indian Consensus Group, with the support of WHO, issued a guideline for defining overweight and obesity among Indians living in India using BMI cut-off values of 23 and 25 kg/m2, respectively.58 In spite of acculturation among migrant groups, ethnic disparities are still observed in percentage body fat and associated cardiovascular and metabolic risks. Given the available evidence, the National Institute of Health and Care Excellence (NICE) in 2012 issued guidelines for South Asians residing in the United Kingdom to be screened for diabetes at BMI levels from 23 kg/m2.59 Also, in a recent position statement, the American Diabetes Association (ADA) recommended that among all Asians living in America screening for diabetes should commence at BMI levels of 23 kg/m2 and higher.60 The BMI cut-off values for overweight and obesity is 24 and 28 kg/m2, respectively, for Chinese and Japanese.61 On the other extreme,
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the BMI cut-off values proposed for identifying overweight and obesity among Pacific Islanders is 26 and 32 kg/m2, respectively.62 More studies are needed to validate these suggested cut-off values among Pacific Islanders.
CUT-OFF VALUES FOR ABDOMINAL OBESITY Compared to total body fat, regional body fat distribution correlates better with adverse cardiovascular and metabolic outcomes of obesity. Abdominal (also known as central) obesity comprises of visceral fat and subcutaneous fat. Specifically, visceral fat and obesityrelated morbidities and mortalities are linked.23–27 Abdominal obesity can be measured with reliable precision using computerized tomography (CT),28 magnetic resonance imaging (MRI),29 and dual-energy X-ray absorptiometry (DEXA).30 These methods can also differentiate visceral fat from subcutaneous fat. Their use in routine clinical practice and population surveys is however limited. The importance of abdominal obesity was acknowledged and brought to the fore by the 1997 World Health Expert Consultation.33 WC, WHR, sagittal abdominal diameter, WHtR, and WTR are useful surrogates to measure abdominal obesity. These anthropometric indices are simple, quick, and cost-effective means of assessing visceral and subcutaneous fat. The cutoff values for these anthropometric indices should reflect health risks rather than just surrogates in the quantification of intra-abdominal fat mass. In other words, in addition to screening and surveillance to determine the prevalence of abdominal obesity, cut-off values should inform on points at which action must be taken to mitigate health challenges at both individual and population levels. Sex-specific cut-off values have been recommended for males and females as they naturally have different body shapes and regional body fat distribution.
WAIST-HIP RATIO The role of the WHR as a surrogate measure of both visceral and subcutaneous fat was established following convincing evidence from longitudinal studies that showed significant associations between abdominal obesity and adverse cardiovascular outcomes.21,22 The WHO set WHR cut-off values as more than 1.0 and 0.85 for males and females, respectively.33 These values indicate abdominal obesity and reflect substantially increased cardiometabolic risks.
WAIST CIRCUMFERENCE WC is a better index of assessing visceral fat compared to WHR and more closely correlated with visceral fat measured by the computed tomographic scan.63 It is a better predictor of adverse cardiovascular and metabolic outcomes of obesity compared to BMI.64 A WHO Expert Consultation reviewed existing data from Caucasians on the association between WC and morbidity and recommended sex-specific cut-off values of higher than 94 cm
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(men) and 80 cm (women).33 These values indicate increased risk. WC greater than 102 cm (men) and 88 cm (women) is indicative of substantially increased cardiometabolic risk.33
WAIST-TO-HEIGHT RATIO The WHtR is an improvement on the WC. Indeed, the WHtR is a better index of assessing visceral fat as well as a better predictor of cardiovascular and metabolic risks compared to WC and BMI.65 A WHtR cut-off value of 0.5 or more identifies not only excess visceral fat but also increased cardiovascular and metabolic risk.66
ETHNICITY AND CENTRAL OBESITY CUT-OFF VALUES The recommendation to keep ones waist-line below half of the height is widely acceptable and without ethnic bias.66–68 The Ashwell Shape Chart is a useful tool for screening for abdominal obesity using the WHtR in all ethnic groups, irrespective of age or gender.67 On the other hand, there are questions on the hitherto WHO set cut-off values for WC and waist-to-hip ratio. This is especially following the debate on the need for ethnic-specific BMI.50 The cardiometabolic risks at the same anthropometric measure (WC, WHR) are not the same across ethnicity.69 For example, compared with white women, abdominal obesity is less associated with adverse cardiometabolic risks and outcomes in black women.70 On the other hand, people of Asian ancestry, particularly South Asians (from India, Bangladesh, and Pakistan) are at increased risk of obesity-related cardiometabolic events compared to other ethnic groups.58,71 Tanaka et al., in their meta-analysis of studies that used computerized tomography to measure abdominal fat, showed significant differences in the visceral fat of Japanese, African-Americans, and Caucasians.72 The National Cholesterol Education Program—Third Treatment Panel (NCEP-ATP III) formerly recommended a single sexspecific cut-off value of WC greater than 102 and 88 cm for men and women, respectively, as part of the diagnosis for metabolic syndrome, irrespective of ethnicity.73 However, the NCEP-ATP III criteria for the diagnosis of abdominal obesity was noted to underestimate the prevalence of metabolic syndrome when applied to adult Asians. For example, Tan et al.74 showed that the optimal cut-off values to diagnose abdominal obesity, and by extension, metabolic syndrome, were >90 and >80 cm in males and females, respectively, among Asians. They had used secondary data on WC from adult male and female Chinese, Malay, and Asian Indians obtained from the 1998 Singapore National Health Survey and subjected the same to the receiver operating characteristics (ROC) analysis to derive this optimal WC in Asians.74 In recognition of ethnic differences, the WHO, together with the International Association for the Study of Obesity (IASO) and the International Obesity Task Force (IOTF), and the NCEP-ATP III have re-defined the cut-off values of WC for the diagnosis of abdominal obesity in metabolic syndrome among Asians as 90 and 80 cm for men and women, respectively.62,75 The International Diabetes Federation (IDF) also recognizes ethnic differences in body fat distribution. The IDF has issued a consensus statement on the sex- and ethnic-specific cut-off
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values for WC used in the definition of abdominal obesity as a component of metabolic syndrome.76 For Europids, the IDF set WC cut-off values of 94 cm or more and 80 cm or more for men and women, respectively. The cut-off value for adult women of Asian (South Asian, Chinese, and Japanese) origin is the same as for Europid women (>80 cm) but 4 cm lower for Asian men compared to Europid men (i.e., 90 vs 94 cm). The IDF recommended that European cut-off values should be applied to sub-Saharan Africans and Arabs (Middle-East and Eastern Mediterranean populations) citing lack of sufficient scientific data. Similarly, ethnic South and Central Americans should apply the same recommendations as for South Asians pending availability of specific data. Emerging data from sub-Saharan Africa, Middle East/ Eastern Mediterranean, and Central America suggest the need for the revision of the European cut-off values for WC recommended for use by the WHO, NCEP-ATP III, and IDF. In sub-Saharan Africa, several studies have shown that applying the IDF recommended cut-off values to identify levels at which WC identifies cardiometabolic risk inappropriate for black Africans.77–82 The CRIBSA study in Cape Town, South Africa, noted that WC cut-off values of 84 cm (men) and 94 cm (women) were optimal in identifying metabolic syndrome.77 Recently, Ekoru et al. published WC cut-off points of 81.2 and 81.0 cm for subSaharan African men and women, respectively, derived using the ROC analysis to identify the presence of two or more components of metabolic syndrome apart from WC.79 The cut-off values were obtained following analysis of data of over 21,000 participants drawn from 17 cross-sectional studies carried out between 1990 and 2014 in eight sub-Saharan countries.79 Another recently conducted cross-sectional study examined WC cut-off values that predict obesity using ROC analysis in apparently healthy adult Nigerians recruited from the six geopolitical zones in Nigeria.83 This study showed that the optimal WC cut-off values for identifying obesity (diagnosed as BMI 30 kg/m2) were >96 and >95 cm for men and women, respectively.83 It is pertinent to note that the studies emanating from sub-Saharan Africa are mostly cross-sectional studies with varying methodologies, thus limiting the inferential value of such studies. The observations, however, suggest that there may be a need for the WC cut-off values to be lowered in men and increased in women when compared to the currently used European cut-off recommended in the region.79 Further large-scale longitudinal studies with standardized methods are needed to provide more convincing evidence to support the call for ethnic-specific cut-off values in sub-Saharan Africa. Similarly, the appropriateness of the use of European cut-off values for WC and WHR to identify metabolic syndrome among ethnic groups from the Middle East and Eastern Mediterranean region is under scrutiny. Several cross-sectional studies from Arab countries have suggested different cut-off values, all of which vary from the recommended European cut-off values.84–88 For example, the proposed optimal WC cut-off values identifying metabolic syndrome for males and females, respectively, is: 92 and 87 cm in Saudi Arabia,84 99 and 97 cm in Iraq,85 99.5 and 91 cm in Qatar,86 89 and 91 cm in Iran,87 and 100.5 and 96.25 cm in Egypt.88 Applying the European cut-off values as recommended by IDF to identify metabolic syndrome led to an overestimation of the prevalence of abdominal obesity in Arab women in these studies. In all, there are strong indications that obesity-related cardiovascular and metabolic risks vary with ethnicity. Currently, aside from the WHtR, there are no universally acceptable cut-off values for the other anthropometric indices used to assess abdominal obesity. Although data on optimal cut-off values of anthropometric indices to predict obesity and its associated cardiometabolic risks are increasing globally, there is need to strengthen the evidence to support the calls to review the use of European cut-off values for WC among sub-Saharan Africans and Arabs. II. MECHANISMS OF OBESITY
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References 1. Deurenberg P, Deurenberg-Yap M, Wang J, Lin FP, Schmidt G. The impact of body build on the relationship between body mass index and percent body fat. Int J Obes Relat Metab Disord. 1999;23(5):537–542. 2. Gasperino J. Ethnic differences in body composition and their relation to health and disease in women. Ethn Health. 1996;1(4):337–347. 3. Editorial BPJ. The fattening room in Nigeria. West J Nurs Res. 1989;11(6):655–656. https://dx.doi.org/ 10.1177/019394598901100601. 4. Steyn K, Damasceno A. Lifestyle and related risk factors for chronic diseases. In: Jamison DT, Feachem RG, Makgoba MW, et al., eds. Disease and mortality in Sub-Saharan Africa. 2nd ed. Washington, DC: The International Bank for Reconstruction and Development/the World Bank; 2006. Available from: https://www.ncbi. nlm.nih.gov/books/NBK2290/#A1627. Accessed on August 27, Vol. 2017. 5. Brewis AA, McGarvey ST, Jones J, Swinburn BA. Perception of body size in Pacific Islanders. Int J Obes Relat Metab Disord. 1998;22(2):185–189. 17. Allison DB, Hoy MK, Fournier A, Heymsfield SB. Can ethnic differences in men’s preferences for women’s body shapes contribute to ethnic differences in female adiposity? Obes Res. 1993;1(6):425–432. https://dx.doi.org/ 10.1002/j.1550-8528.1993.tb00024.x. 7. Owen PR, Laurel-Seller E. Weight and shape ideals: thin is dangerously in. J Appl Soc Psychol. 2000;30(5):979–990. https://dx.doi.org/10.1111/j.1559-1816.2000.tb02506.x. 8. Ryan EL. Is ugly the new beautiful? An investigation of perceptions of beauty by young female viewers of ugly Betty in the US. J Mass Commun Journalism. 2013;3155https://dx.doi.org/10.4172/2165-7912.1000155. 9. Christopoulou-Aletra H, Papavramidou N. Methods used by the Hippocratic physicians for weight reduction. World J Surg. 2004;28(5):513–517. https://dx.doi.org/10.1007/s00268-004-7373-9. 10. Cheyne G. An Essay of Health and Long Life. London: George Strahan & J. Leake; 1724. Available from: https://ia801406. us.archive.org/19/items/anessayhealthan00cheygoog/anessayhealthan00cheygoog.pdf. Accessed 9 January 2018. 11. Enzi G, Busetto L, Inelmen EM, Coin A, Sergi G. Historical perspective: visceral obesity and related comorbidity in Joannes Baptista Morgagni’s ’De sedibus et causis morborum per anatomen indagata. Int J Obes Relat Metab Disord. 2003;27(4):534–535. 12. Charlton A. George Cheyne (1671 or 73-1743): 18th-century physician. J Med Biogr. 2011;19(2):49–55. https://dx. doi.org/10.1258/jmb.2010.010028. 13. Vague J. La differenciation sexuelle. Facteur determinant des formes de l’obesite. Presse Med. 1947;55(30):339–340. 14. TOS obesity as a disease writing group, Allison DB, Downey M, et al. Obesity as a disease: a white paper on evidence and arguments commissioned by the Council of The Obesity Society. Obesity. 2008;16(6):1161–1177. https://dx.doi.org/10.1038/oby.2008.231. 15. Komaroff M. For researchers on obesity: historical review of extra body weight definitions. J Obes. 2016;2016:2460285. 9 pages, https://doi.org/10.1156/2016/2460285. 16. Metropolitan Life Insurance Company. New weight standards for men and women. Stat Bull Metropol Life Insur Co. 1959;40:1–4. 17. Eknoyan G. Adolphe Quetelet (1796-1874)—the average man and indices of obesity. Nephrol Dial Transplant. 2008;23(1):47–51. 18. Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL. Reprints and reflections: indices of relative weight and obesity. Int J Epidemiol. 2014;43(3):655–665. 19. Okorodudu DO, Jumean MF, Montori VM, et al. Diagnostic performance of body mass index to identify obesity as defined by body adiposity: a systematic review and meta-analysis. Int J Obes (Lond). 2010;34(5):791–799. 20. World Health Organization (WHO). Waist Circumference and Waist-Hip Ratio: Report of a WHO Expert Consultation. Geneva: World Health Organization (WHO); 2008. 21. Larsson B, Svardsudd K, Welin L, et al. Abdominal adipose tissue distribution, obesity, and risk of cardiovascular disease and death: 13 years follow up of participants in the study of men born in 1913. Br Med J. 1984;288 (6428):1401–1404. 22. Lapidus L, Bengtsson C, Larsson B, et al. Distribution of adipose tissue and risk of cardiovascular disease and death: a 12 year follow up of participants in the population study of women in Gothenburg, Sweden. Br Med J. 1984;289(6454):1257–1261. 23. Yusuf S, Hawken S, Ounpuu S, et al. Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study): case-control study. Lancet. 2004;364(9438):937–952.
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24. de Koning L, Merchant AT, Pogue J, Anand SS. Waist circumference and waist-to-hip ratio as predictors of cardiovascular events: meta-regression analysis of prospective studies. Eur Heart J. 2007;28:850–856. https://dx.doi. org/10.1093/eurheartj/ehm026. 25. Zhang C, Rexrode KM, van Dam RM, Li TY, Hu FB. Abdominal obesity and the risk of all-cause, cardiovascular, and cancer mortality: sixteen years of follow-up in US women. Circulation. 2008;117(13):1658–1667. 26. Gruson E, Montaye M, Kee F, et al. Anthropometric assessment of abdominal obesity and coronary heart disease risk in men: the PRIME study. Heart. 2010;96(2):136–140. 27. Czernichow S, Kengne A, Huxley RR, et al. Comparison of waist-to-hip ratio and other obesity indices as predictors of cardiovascular disease risk in people with type-2 diabetes: a prospective cohort study from ADVANCE. Eur J Prev Cardiol. 2011;18(2):312–319. 28. Borkan GA, Gerzof SG, Robbins AH, et al. Assessment of abdominal fat content by computed tomography. Am J Clin Nutr. 1982;36(1):172–177. 29. Staten MA, Totty WG, Kohrt WM. Measurement of fat distribution by magnetic resonance imaging. Invest Radiol. 1989;24(5):345–349. 30. Kaul S, Rothney MP, Peters DM, et al. Dual-energy x-ray absorptiometry for quantification of visceral fat. Obesity (Silver Spring). 2012;20(6):1313–1318. https://dx.doi.org/10.1038/oby.2011.393. 31. World Health Organization. Health Topics: Obesity. Available from: http://www.who.int/topics/obesity/en/. Accessed on January 23, 2018. 32. World Health Organization (WHO). Physical Status: the use and interpretation of anthropometry. Report of a WHO Expert Committee. In: WHO Technical Report Series. Geneva: World Health Organization; 1995:Vol. 854. 33. World Health Organization (WHO). Obesity: Preventing and Managing the Global Epidemic. Report of a WHO Consultation (TRS 894), Geneva: World Health Organization (WHO); 2000. 34. Aloia JF, Vaswani A, Mikhail M, Flaster ER. Body composition by dual-energy x-ray absorptiometry in black compared with white women. Osteoporos Int. 1999;10(2):114–119. 35. Rahman M, Berenson AB. Racial differences in lean mass distribution among reproductive-aged women. Ethn Dis. 2010;20(4):346–352. 36. Deurenberg P, Yap M, van Staveren W. Body mass index and percent body fat: a meta-analysis among different ethnic groups. Int J Obes Relat Metab Disord. 1998;22(12):1164–1171. 37. Deurenberg-Yap M, Schmidt G, van Staveren WA, Deurenberg P. The paradox of low body mass index and high body fat percentage among Chinese, Malays and Indians in Singapore. Int J Obes Relat Metab Disord. 2000;24 (8):1011–1017. 38. Chang CJ, Wu CH, Chang CS, et al. Low body mass index but high percent body fat in Taiwanese subjects: implications of obesity cutoff. Int J Obes (Lond). 2003;27:253–259. 39. Ko G, Tang J, Chan J, et al. Lower BMI cutoff value to define obesity in Hong Kong Chinese: an analysis based on body fat assessment by bioelectrical impedance. Br J Nutr. 2001;85:239–242. 40. Deurenberg P, Deurenberg-Yap M, Guricci S. Asians are different from Caucasians and from each other in their body mass index/body fat per cent relationship. Obes Rev. 2002;3(3):141–146. 41. Carpenter CL, Yan E, Chen S, et al. Body fat and body mass index among a multiethnic sample of college-age men and women. J Obes. 2013;2013. 790654, 7 pages, https://doi.org/10.1155/2013/790654. 42. Shai I, Jiang R, Manson JE, et al. Ethnicity, obesity, and risk of type 2 diabetes in women: a 20-year follow-up study. Diabetes Care. 2006;29:1585–1590. 43. Moon O, Kim N, Jang S, Yoon T, Kim S. The relationship between body mass index and the prevalence of obesityrelated diseases based on the 1995 National Health Interview Survey in Korea. Obes Rev. 2002;3:191–196. 44. Deurenberg-Yap M, Chew SK, Deurenberg P. Elevated body fat percentage and cardiovascular risks at low body mass index levels among Singaporean Chinese, Malays and Indians. Obes Rev. 2002;3(3):209–215. 45. Davis J, Juarez D, Hodges K. Relationship of ethnicity and body mass index with the development of hypertension and hyperlipidemia. Ethn Dis. 2013;23(1):65–70. 46. Wen CP, David Cheng TY, Tsai SP, et al. Are Asians at greater mortality risks for being overweight than Caucasians? Redefining obesity for Asians. Public Health Nutr. 2009;12(4):497–506. 47. Razak F, Anand SS, Shannon H, et al. Defining obesity cut points in a multiethnic population. Circulation. 2007;115 (16):2111–2118. 48. Misra A. Revision of limits of body mass index to define overweight and obesity are needed for the Asian ethnic groups. Int J Obes Relat Metab Disord. 2003;27:1294–1296.
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49. Misra A. Ethnic-specific criteria for classification of body mass index: a perspective for Asian Indians and American Diabetes Association position statement. Diabetes Technol Ther. 2015;17(9):667–671. 50. World Health Organization (WHO) Expert Consultation. Appropriate body mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363:157–163. 51. Lear SA, Humphries KH, Kohli S, Birmingham CL. The use of BMI and waist circumference as surrogates of body fat differs by ethnicity. Obesity. 2007;15:2817–2824. 52. Wang D, Li Y, Lee SG, et al. Ethnic differences in body composition and obesity related risk factors: study in Chinese and white males living in China. PLoS ONE. 2011;6(5). e19835. https://doi.org/10.1371/journal.pone.0019835. 53. Ma RCW, Chan JCN. Type 2 diabetes in East Asians: similarities and differences with populations in Europe and the United States. Ann N Y Acad Sci. 2013;1281:64–91. https://dx.doi.org/10.1111/nyas.12098. 54. Debate SJ. Ethnic-specific revisions of body mass index cutoffs to define overweight and obesity in Asians are not warranted. Int J Obes (Lond). 2003;27:1297–1299. 55. Stevens J, Juhaeri CJ, Jones D. The effect of decision rules on the choice of a body mass index cutoff for obesity: examples from African American and white women. Am J Clin Nutr. 2002;75:986–992. 56. Stevens J, Nowicki E. Body mass index and mortality in Asian populations: implications for obesity cutpoints. Nutr Rev. 2003;61(3):104–107. 57. Steven J. Commentary: ethnic-specific cutpoints for obesity vs country-specific guidelines for action. Int J Obes (Lond). 2003;27:287–288. https://dx.doi.org/10.1038/sj.ijo.802255. 58. Misra A, Chowbey P, Makkar BM, et al. Consensus statement for diagnosis of obesity, abdominal obesity and the metabolic syndrome for Asian Indians and recommendations for physical activity, medical and surgical management. J Assoc Physicians India. 2009;57:163–170. 59. National Institute of Health and Care Excellence. Preventing type 2 diabetes risk: identification and interventions for individuals at high risk. 2012. Available from: www.nice.org.uk/guidance/ph38/resources/ guidance-preventing-type2-diabetes-riskidentification-and-interventions-for-individuals-at-high-riskpdf. Assessed January 16, 2018. 60. American Diabetes Association. Standards for medical care in diabetes—2015. Diabetes Care. 2015;38(Suppl 1): S1–S94. 61. Kanazawa M, Yoshiike N, Osaka T, Numba Y, Zimmet P, Inoue S. Criteria and classification of obesity in Japan and Asia-Oceania. World Rev Nutr Diet. 2005;94:1–12. https://dx.doi.org/10.1159/000088200. 62. World Health Organization Western Pacific Region (WPRO). International Association for the Study of Obesity (IASO), International Obesity Task /IOTF. The Asia-Pacific perspective: Redefining Obesity and Its Treatment. Geneva: World Health Organization; 2000. 63. Pouliot MC, Despres JP, Lemieux S, et al. Waist circumference and abdominal sagittal diameter: best simple anthropometric indexes of abdominal visceral adipose tissue accumulation and related cardiovascular risk in men and women. Am J Cardiol. 1994;73(7):460–468. 64. Klein S, Allison DB, Heymsfield SB, et al. Waist circumference and cardiometabolic risk. A consensus statement from shaping America’s health: association for Weight Management and Obesity Prevention; NAASO, the Obesity Society; the American Society for Nutrition; and the American Diabetes Association. Diabetes Care. 2007;30 (6):1647–1652. https://dx.doi.org/10.2337/dc07-9921. 65. Ashwell M, Gunn P, Gibson S. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: systematic review and meta-analysis. Obes Rev. 2012;13(3):275–286. https:// dx.doi.org/10.1111/j.1467-789X.2011.00952.x. 66. Browning LM, Hsieh SD, Ashwell M. A systematic review of waist-to-height ratio as a screening tool for the prediction of cardiovascular disease and diabetes: 0.5 could be a suitable global boundary value. Nutr Res Rev. 2010;23(2):247–269. 67. Ashwell M, Gibson S. A proposal for a primary screening tool: keep your waist circumference to less than half your height. BMC Med. 2014;12207. https://dx.doi.org/10.1186/s12916-014-0207-1. 68. Ashwell M, Gibson S. Waist to height ratio is a simple and effective obesity screening tool for cardiovascular risk factors: analysis of data from the British National Diet and Nutrition Survey of Adults aged 19-64 years. Obes Facts. 2009;2:97–103. https://dx.doi.org/10.1159/000203363. 69. Lear SA, James PT, Ko GT, Kumanyika S. Appropriateness of waist circumference and waist-to-hip ratio cutoffs for different ethnic groups. Eur J Clin Nutr. 2010;64(1):42–61. https://dx.doi.org/10.1038/ejcn.2009.70. 70. Dowling HJ, Pi-Sunyer FX. Race-dependent health risks of upper body obesity. Diabetes. 1993;42:537–543.
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71. McKeigue PM. Metabolic consequences of obesity and body fat pattern: lessons from migrant studies. In: Chadwick DJ, Cardew GC, eds. The origins and consequences of obesity. Chichester: Wiley; 1996:54–67. [Ciba Foundation Symposium 201]. 72. Tanaka S, Horimai C, Katsukawa F. Ethnic differences in abdominal visceral fat accumulation between Japanese, African-Americans, and Caucasians: a meta-analysis. Acta Diabetol. 2003;40(Suppl 1):S302–S304. https://dx.doi. org/10.1007/s00592-003-0093-z. 73. Executive summary of the third report of the National Cholesterol Education Program. (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (adult treatment panel III). JAMA. 2001;285:2486–2497. 74. Tan CE, Ma S, Wai D, Chew SK, Tai ES. Can we apply the National Cholesterol Education Program Adult Treatment Panel definition of metabolic syndrome to Asians? Diabetes Care. 2004;27(5):1182–1186. 75. International Diabetes Federation (IDF). The IDF consensus worldwide definition of the metabolic syndrome. In: International Diabetes Federation (IDF). 2006. 76. Grundy SM, Cleeman JI, Daniels SR, et al. Diagnosis and management of the metabolic syndrome: an American Heart Association/National Heart, Lung, and Blood Institute scientific statement. Circulation. 2005;112 (17):2735–2752. 77. Peer N, Steyn K, Levitt N. Differential obesity indices identify the metabolic syndrome in Black men and women in Cape Town: the CRIBSA study. J Pub Health. 2015;38(1):175–182. https://dx.doi.org/10.1093/pubmed/fdu115. 78. Crowther NJ, Norris SA. The current waist circumference cut point used for the diagnosis of metabolic syndrome in sub-Saharan African women is not appropriate. PLoS One. 2012;7. e48883. https://dx.doi.org/10.1371/journal. pone.0048883. 79. Ekoru K, Murphy GAV, Young EH, et al. Deriving an optimal threshold of waist circumference for detecting cardiometabolic risk in sub-Saharan Africa. Int J Obes (Lond) 2017:1–8. https://doi.org/10.1038/ijo.2017.240 ([ahead of print]) 80. Magalha˜es P, Capingana DP, Mill JG. Prevalence of the metabolic syndrome and determination of optimal values of waist circumference in university employees from Angola. Cardiovasc J Afr. 2014;25(1):27–33. https://dx.doi. org/10.5830/CVJA-2013-086. 81. Motala AA, Esterhuizen T, Pirie FJ, Omar MA. The prevalence of metabolic syndrome and determination of the optimal waist circumference cutoff points in a rural South African community. Diabetes Care. 2011;34:1032–1037. 82. Hoebel S, Malan I, De Ridder JH. Determining ethnic-, gender-, and age-specific waist circumference cut-off points to predict metabolic syndrome: the sympathetic activity and ambulatory blood pressure in Africans (SABPA) study. JEMDSA. 2013;18(2):88–96. 83. Okafor CI, Raimi TH, Gezawa ID, et al. Performance of waist circumference and proposed cutoff levels for defining overweight and obesity in Nigerians. Ann Afr Med. 2016;15(4):185–193. 84. Al-Rubean K, Youssef AM, AlFarsi Y, et al. Anthropometric cutoff values for predicting metabolic syndrome in a Saudi community: from the SAUDI-DM study. Ann Saudi Med. 2017;37(1):21–30. https://dx.doi.org/ 10.5144/0256-4947.2017.21. 85. Mansour AA, Al-Hassan AA, Al-Jazairi MI. Cut-off values for waist circumference in rural Iraqi adults for the diagnosis of metabolic syndrome. Rural Remote Health. 2007;7(4):765. Available from: https://www.rrh.org. au/journal/article/765. Accessed 15 January 2018. 86. Bener A, Yousafzai MT, Darwish S, Al-Hamaq AO, Nasralla EA, Abdul-Ghani M. Obesity index that better predict metabolic syndrome: body mass index, waist circumference, waist hip ratio, or waist height ratio. J Obes. 2013;2013269038. 87. Delavari A, Forouzanfar MH, Alikhani S, Sharifian A, Kelishadi R. First nationwide study of the prevalence of the metabolic syndrome and optimal cutoff points of waist circumference in the Middle East: the national survey of risk factors for noncommunicable diseases of Iran. Diabetes Care. 2009;32:1092–1097. 88. Assaad-Khalil SH, Mikhail MM, Aati TA, et al. Optimal waist circumference cutoff points for the determination of abdominal obesity and detection of cardiovascular risk factors among Egyptian population. Indian J Endocr Metab. 2015;19:804–810. https://dx.doi.org/10.4103/2230-8210.167556.
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17 Ethnicity and Cut-Off Values in Obesity Ejiroghene Martha Umuerri Department of Medicine, Delta State University, Abraka, Nigeria
O U T L I N E Introduction
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Waist-Hip Ratio
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Ethnicity and Perception of Obesity
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Waist Circumference
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Waist-to-Height Ratio
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Definition and Measurement of Obesity: Historical Perspective 212 Cut-Off Values for BMI
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Ethnicity and Central Obesity Cut-Off Values
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Ethnic-Specific BMI Cut-Off Values
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References
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Cut-Off Values for Abdominal Obesity 217
INTRODUCTION The human body composition made up of fat mass and fat-free masses (blood, bone, skeletal muscles, visceral organs) accounts for variations in the human body frame. Human variations in body size and habitus are age-long. Genetic, social, cultural, environmental, and economic factors have influenced the diverse phenotypic expression of body size in humans. Persons with large body size have existed throughout human history. One of the contributory factors to large body size is an excess accumulation of fat. The fat mass and “fat-free” masses differ not only with age and sex but also with ethnicity.1,2 Although difficult to define, ethnicity usually refers to a group of people identified by shared similarities in their sociocultural values, beliefs, and practices. For example, people of the same ethnic group share similar genetic characteristics as well as lifestyles such as food choices, occupation, and recreational
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activities. Hence, similarities in body size and shape among people of the same ethnicity are not surprising. This chapter shall focus on ethnicity and obesity cut-off values among adults.
ETHNICITY AND PERCEPTION OF OBESITY Obesity refers to the condition in which there is an excess accumulation of fat mass. The prevalence of obesity has been noted to increase in the past three decades significantly. In a considerable part of human history, large body size has been associated with status, affluence, beauty, and sometimes good health. Indeed, prehistoric statuettes of abdominally obese women such as the Venus of Willendorf and other Venus figurines were not uncommon and were thought to portray success and fertility. It used to be an acceptable cultural practice among some ethnic groups in West Africa for young girls to be kept in the fattening room to make them plump and beautiful. For example, among the Annang people of Nigeria, young ladies were held and nurtured for a variable period in their father’s compound until they are big enough as part of the cultural practices before marriage.3 Women who are fat were perceived to be more fertile and adequately nourished to breastfeed their babies for up to 2 years. This custom was not only as part of preparations for a successful reproductive career after marriage but also a prerequisite to being initiated into the prestigious secret cult of married women. The perception of body size still varies somewhat with ethnicity. Positive cultural values for large body size hold sway in some ethnic groups around the world especially in subSaharan Africa and the Pacific Islands.4,5 Men who are big are often well respected as they are perceived to be wealthy. Women with full-bodied habitus are viewed as attractive and well-cared for in some cultures. In a study in the United States, black and Hispanic men preferred women who are fat compared to white and Asian men.6 Culture is however evolving. In westernized cultures as seen in many developed and some developing countries, a negative perception of obesity is favored, especially among young people. This opinion is not necessarily for health reasons. Persons with slender built are perceived to be trendy. The mass media has helped in no small way to influence this mindset.7,8
DEFINITION AND MEASUREMENT OF OBESITY: HISTORICAL PERSPECTIVE The concept of obesity and its relationship with health status is not entirely contemporary but dates back to the Hippocrates era. Obesity, akin to large body size, was linked with infertility and premature deaths.9 About 250 years ago, the link between obesity and disease was reaffirmed by the independent works of George Cheyne MD (1671–1743), a renowned physician and Joannes Baptista Morgagni (1698–1771), the legendary Italian physician cum anatomist.10,11 Cheyne, who himself suffered from obesity, attested firsthand to the adverse health consequences of obesity including depression and nervous disorders.12 In particular, Morgagni noted the link between the distribution of body fat and diseases such as hypertension, hyperuricemia, and atherosclerosis. He reported visceral fat in the abdomen and
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mediastinum as the culprit.11 In the mid-20th century, Jean Vague, a French physician and Professor at the University of Marseille, documented observed differences in metabolic complications associated with regional fat distribution.13 He noted that upper body fat centered around the abdomen, which he named android obesity, was a risk factor for cardiometabolic diseases. On the hand, lower body fat distributed around the hips, gynoid obesity was not associated with adverse metabolic consequences. Since then, several other researchers have linked abdominal obesity with more adverse health outcomes compared with general obesity. Although obesity cannot be considered a disease in its entirety, the link between excess body fat and its regional distribution and health challenges is not in contention and preventive measures put in place.14 The definition of obesity has however evolved. Several efforts have been made to define ideal body size as well as one with an increased propensity to medical conditions. About 25 centuries ago, in the Hippocrates era, obesity was defined as having excess “humors” or body fluids, that is phlegm, yellow bile, black bile, and blood.15 In an attempt to define an ideal or average body weight, Lambert Adolphe Quetelet (1796–1874), a Belgian mathematician and statistician conducted a study in the mid-19th century that revealed that the increase in weight of an individual was a function of the square of the individual’s height. His work led to the formation of a table of average body weight for Belgian adults.15 Quetelet’s intent, however, was not to define obesity or excess body fat and his proposed anthropometric index, defined as a ratio of the body weight to the square of the height, was not utilized for this purpose until several decades later. Actuarial tables were references put together by the life insurance industry to obtain ideal body weight. Data derived from observed sex-specific weight-for-height associated with minimal mortality were used to compute these tables.16 These actuarial tables were not without flaws. Before the 1970s, body weight in proportion to height in diverse functions was used as an anthropometric indice and surrogate to measure body fat, even though none of the indices then was considered universally as the benchmark.15,17,18 In a quest to find the anthropometric index that will best indicate fatness or obesity among the existing indices, Professor Ancel Benjamin Keys (1904–2004), an American physiologist at the University of Minnesota, led a large comparative multinational study.17 In this study, over 7000 apparently healthy men from 5 countries were recruited across the globe—United States of America, South Africa, Japan, Italy, and Finland. The height and weight of lightly clothed and barefooted participants were measured and anthropometric indices calculated—weight-to-height (W/H), weight-to-squared height (W/H2), and weight-to-cubed height (W/H3) (the ponderal index). Body fatness was measured using body density obtained via underwater weighing, a relatively hard and time-consuming procedure, and skin-fold thickness at specific sites. The calculated anthropometric indices were compared to ascertain which one best correlated with body fatness. Although the study participants were not fully representative of the general population, the weight-to-squared height (W/H2), which is the same as Quetelet’s index, stood out as the best index. Keys and colleagues published their findings in 1972 and renamed this anthropometric index as the body mass index (BMI).17 Since the 1980s, the United States National Institutes of Health (NIH) have advocated and popularized the use of the BMI as a means of assessing body fat. Although the landmark study by Keys et al. did not include women and was for use at population levels, BMI is used to assess adiposity in both men and women, and across different age groups at individual and population levels.19 Till date, the BMI, a cheap and quick
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method of assessing adiposity, is the most widely used anthropometric index to define obesity for clinical and epidemiological purposes. In addition to anthropometric indices derived from weight and height, waist and hip circumferences were used to obtain the waist-hip ratio (WHR), an anthropometric index of abdominal adiposity.20 The World Health Organization (WHO) recommends that the waist circumference (WC) is measured at the mid-point between the lower border of the ribcage and the top of the iliac crest while measurement for the hip circumference is at the fullest part of the buttocks, usually around the greater trochanter.20 In two separate longitudinal studies in Sweden, Larsson et al.21 and Lapidus et al.22 showed that WHR was an independent risk factor for obesity-related cardiometabolic mortality and morbidity among men and women, respectively, indeed reaffirming the integrity of the earlier submissions by Morgagni11 and Vague13 on the significance of regional fat distributions and its strong correlation with adverse cardiovascular events.11 In addition to the WHR, other anthropometric indices have been validated to assess abdominal obesity. These include the WC, waist-to-height ratio (WHtR), the waist-to-thigh ratio (WTR), sagittal abdominal diameter, and the abdominal diameter index (sagittal abdominal diameter to mid-thigh girth ratio). The WC is easy to measure and interpret and correlates well with visceral fat. Like the WHR, the WTR helps to differentiate upper body (android) obesity from the lower body (gynoid) obesity, although its predictive values are higher than WHR. Several studies have shown that abdominal obesity has a stronger predictive value for adverse cardiovascular outcomes like stroke and coronary artery disease and death than general obesity measured by BMI.23–27 In the assessment of generalized and central obesity, there were remarkable technological advances in the 20th century.28–30 These include the use of computerized tomography (CT), magnetic resonance imaging (MRI), and dual-energy X-ray absorptiometry (DEXA) to estimate percentage body fat as well as regional fat distribution. Unlike anthropometry, these methods are costly, time-consuming and require high-level expertise in the procedure and interpretation thus, limiting their routine use at both individual and population levels.
CUT-OFF VALUES FOR BMI The WHO defines obesity as a medical condition in which excess accumulation of body fat results in adverse health outcomes.31 Obesity and numerous multi-systemic health conditions are linked. These include dermatologic, musculoskeletal, neuropsychiatric, respiratory, and cardiometabolic disorders such as hypertension, diabetes, stroke, and coronary heart disease, as well as specific cancers. The direct economic and social costs of obesity are enormous. Unfortunately, with globalization and the increasing adoption of lifestyles that favor a positive energy balance (energy intake more than energy expenditure), the prevalence of obesity has attained a pandemic proportion. Likewise, the incidence of type 2 diabetes is escalating globally. This concurrence calls for urgent action. The need for an appropriate anthropometric indicator and optimum cut-off value for BMI led to the constitution of a WHO Expert Committee on Physical Status with over one hundred experts in 1991.32 Following evaluation of series of scientific research and reviews, the WHO in 1995 published a technical report of the Expert Committee. Anthropometric indicators were chosen based on the identification of “at
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risk” individuals or populations, prediction on benefits of interventions at individual and population levels, assessment of response to interventions, and normative reference. Another WHO Expert Consultation met in 1997, and healthy weight-for-height was put at a BMI of 18.5–24.9 kg/m2 while 25 and 30 kg/m2 were recommended as the BMI cut-off values for overweight and obesity in adults Caucasians, respectively.33 Although the BMI cut-off values were approved based on observed obesity-related mortality and morbidity rates, they were just appropriate for identifying increased adiposity and not as targets for interventions in isolation. Until recently, the WHO BMI cut-off values were applied globally without recourse to ethnic differences.
ETHNIC-SPECIFIC BMI CUT-OFF VALUES Ethnic differences in body composition have been demonstrated using dual-energy X-ray absorptiometry (DEXA). Using the DEXA method to access body composition, black women have been shown to have a higher bone and muscle mass, and a lower fat mass compared to white and Hispanic women at the same BMI levels.34,35 Asians compared with Caucasians, African-Americans, and Pacific Islanders have smaller body frames and thus lower BMIs. For instance, assuming the WHO BMI cut-off values for overweight and obesity were equated to percentage body fat, it pre-supposes that the cardiovascular and metabolic risks associated with obesity will be least among Asians. On the contrary, these risks are higher among Asians compared to other ethnic groups, disproving the veracity of this assumption. Several studies have shown ethnic variations between the WHO BMI cut-off values and percentage body fat, and the observed obesity-related cardiometabolic outcomes.36–47 Although Asians have a lower BMI compared with other ethnic groups, their percentage body fat is paradoxically higher for the same BMI. Deurenberg et al.40 in their review of the available literature showed that for a given BMI, Asians had a 3%–5% point higher percentage body fat compared to Caucasians. Conversely, for a given percentage body fat, Asians had a 3–4 unit lower BMI. In a 20-year prospective study (1980–2000) of over 78,000 apparently healthy women,42 although gaining weight was associated with increased risk of developing type 2 diabetes, the risk was highest among Asians. Observations from this study revealed that at the same BMI, the risk of developing type 2 diabetes among Asians was significantly higher than that of the Caucasians. Similarly, blacks and Hispanics in this study had a higher risk of developing type 2 diabetes compared with Caucasians, but less than the Asians.42 Davis and colleagues also demonstrated the higher propensity of Asians to develop hypertension and hyperlipidemia compared to their counterpart Pacific Islanders and Caucasians with similar BMI.45 In another longitudinal study of over 36,000 adults, the all-cause mortality from obesity at any given BMI above 25 kg/m2 was higher among Asians compared to Caucasians.46 Equating BMI with percentage body fat across different ethnic populations may have far-reaching implications that can be detrimental to overall public health in some populations. The ethnic differences in obesity-related outcomes are not surprising as the percentage body fat, rather than BMI, is the critical factor in defining adiposity. Therefore, the appropriateness of using a generic BMI cut-off value as a surrogate of adiposity irrespective of ethnicity begs for review. Proponents of this view have called on the WHO and other international organizations to review and recommend ethnic-specific BMI cut-off values for obesity.48,49
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In 2002, a WHO expert consultation meeting examined and agreed with available scientific evidence supporting the paradoxical low BMI and high percentage body fat, and the higher cardiometabolic risks of Asians compared to Caucasians.50 Aside from inter-ethnic differences in fat mass, there are differences even within the same ethnic groups.40 For example, in a study of apparently healthy adults of European, Chinese, and South Asian origin, BMI was compared with percentage body fat derived using DEXA.51 At any given BMI, the percentage body fat of the Chinese and the European participants was similar whereas it was 3.9% higher among the South Asians.51 However, in other studies, Chinese were reported to have higher percentage body fat at any BMI compared with Europeans.36,37,52 Also, compared with Caucasians, Chinese and other East Asians have a higher prevalence of obesity-related cardiometabolic risk factors, particularly type 2 diabetes.52,53 The need for ethnic-specific BMI cut-off values is however not without controversies. There are a few opponents to the position that the WHO BMI cut-off values33 should give way to new ethnic-specific BMI values. One of such opponents is Professor June Stevens.54–56 In her opinion, the call for ethnic-specific BMI values needs to be viewed carefully without prejudice to any political undertone. She hinged her arguments against ethnic-specific BMI cut-off values on three points.57 First, obesity cut-off points are arbitrary numbers that should be based on risk rather than percentage body fat. Furthermore, when making comparisons between and within ethnic groups care must be taken to match study designs and measures used to identify risks.46,57 If the needed scientific thoroughness is not applied, there may be significant flaws in inferences made. Second, she opined that there are not enough data to support a higher mortality rate among Asians compared with Caucasians at BMI >25 kg/m2.56,57 Lastly, to single out ethnicity as the basis for redefining obesity cut-off will be a hard task to substantiate socially, environmentally, and politically, particularly as other factors influence variations in BMI.57 However, she supports the call for different nations to set BMI thresholds for public health intervention as deemed applicable. In spite of affirming evidence from existing data, the WHO Expert Consultation did not recommend a new BMI cut-off value for Asians because of the inherent complexities.50 Instead, in their report, they made a distinction between the use of BMI cut-off for defining obesity as a disease and the use of the cut-off values as action points. The WHO Expert Consultation group recognized the BMI as a continuous variable and therefore recommended targets for public health interventions instead. Among Asians, putting the total cardiovascular and metabolic risks together, the recommended BMI cut-off values for initiating interventions for “increased risk” and “high risk” are 23 and 25 kg/m2, respectively.50 Nationalities were encouraged to develop their country-specific cut-off values. In 2009, the Indian Consensus Group, with the support of WHO, issued a guideline for defining overweight and obesity among Indians living in India using BMI cut-off values of 23 and 25 kg/m2, respectively.58 In spite of acculturation among migrant groups, ethnic disparities are still observed in percentage body fat and associated cardiovascular and metabolic risks. Given the available evidence, the National Institute of Health and Care Excellence (NICE) in 2012 issued guidelines for South Asians residing in the United Kingdom to be screened for diabetes at BMI levels from 23 kg/m2.59 Also, in a recent position statement, the American Diabetes Association (ADA) recommended that among all Asians living in America screening for diabetes should commence at BMI levels of 23 kg/m2 and higher.60 The BMI cut-off values for overweight and obesity is 24 and 28 kg/m2, respectively, for Chinese and Japanese.61 On the other extreme,
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the BMI cut-off values proposed for identifying overweight and obesity among Pacific Islanders is 26 and 32 kg/m2, respectively.62 More studies are needed to validate these suggested cut-off values among Pacific Islanders.
CUT-OFF VALUES FOR ABDOMINAL OBESITY Compared to total body fat, regional body fat distribution correlates better with adverse cardiovascular and metabolic outcomes of obesity. Abdominal (also known as central) obesity comprises of visceral fat and subcutaneous fat. Specifically, visceral fat and obesityrelated morbidities and mortalities are linked.23–27 Abdominal obesity can be measured with reliable precision using computerized tomography (CT),28 magnetic resonance imaging (MRI),29 and dual-energy X-ray absorptiometry (DEXA).30 These methods can also differentiate visceral fat from subcutaneous fat. Their use in routine clinical practice and population surveys is however limited. The importance of abdominal obesity was acknowledged and brought to the fore by the 1997 World Health Expert Consultation.33 WC, WHR, sagittal abdominal diameter, WHtR, and WTR are useful surrogates to measure abdominal obesity. These anthropometric indices are simple, quick, and cost-effective means of assessing visceral and subcutaneous fat. The cutoff values for these anthropometric indices should reflect health risks rather than just surrogates in the quantification of intra-abdominal fat mass. In other words, in addition to screening and surveillance to determine the prevalence of abdominal obesity, cut-off values should inform on points at which action must be taken to mitigate health challenges at both individual and population levels. Sex-specific cut-off values have been recommended for males and females as they naturally have different body shapes and regional body fat distribution.
WAIST-HIP RATIO The role of the WHR as a surrogate measure of both visceral and subcutaneous fat was established following convincing evidence from longitudinal studies that showed significant associations between abdominal obesity and adverse cardiovascular outcomes.21,22 The WHO set WHR cut-off values as more than 1.0 and 0.85 for males and females, respectively.33 These values indicate abdominal obesity and reflect substantially increased cardiometabolic risks.
WAIST CIRCUMFERENCE WC is a better index of assessing visceral fat compared to WHR and more closely correlated with visceral fat measured by the computed tomographic scan.63 It is a better predictor of adverse cardiovascular and metabolic outcomes of obesity compared to BMI.64 A WHO Expert Consultation reviewed existing data from Caucasians on the association between WC and morbidity and recommended sex-specific cut-off values of higher than 94 cm
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(men) and 80 cm (women).33 These values indicate increased risk. WC greater than 102 cm (men) and 88 cm (women) is indicative of substantially increased cardiometabolic risk.33
WAIST-TO-HEIGHT RATIO The WHtR is an improvement on the WC. Indeed, the WHtR is a better index of assessing visceral fat as well as a better predictor of cardiovascular and metabolic risks compared to WC and BMI.65 A WHtR cut-off value of 0.5 or more identifies not only excess visceral fat but also increased cardiovascular and metabolic risk.66
ETHNICITY AND CENTRAL OBESITY CUT-OFF VALUES The recommendation to keep ones waist-line below half of the height is widely acceptable and without ethnic bias.66–68 The Ashwell Shape Chart is a useful tool for screening for abdominal obesity using the WHtR in all ethnic groups, irrespective of age or gender.67 On the other hand, there are questions on the hitherto WHO set cut-off values for WC and waist-to-hip ratio. This is especially following the debate on the need for ethnic-specific BMI.50 The cardiometabolic risks at the same anthropometric measure (WC, WHR) are not the same across ethnicity.69 For example, compared with white women, abdominal obesity is less associated with adverse cardiometabolic risks and outcomes in black women.70 On the other hand, people of Asian ancestry, particularly South Asians (from India, Bangladesh, and Pakistan) are at increased risk of obesity-related cardiometabolic events compared to other ethnic groups.58,71 Tanaka et al., in their meta-analysis of studies that used computerized tomography to measure abdominal fat, showed significant differences in the visceral fat of Japanese, African-Americans, and Caucasians.72 The National Cholesterol Education Program—Third Treatment Panel (NCEP-ATP III) formerly recommended a single sexspecific cut-off value of WC greater than 102 and 88 cm for men and women, respectively, as part of the diagnosis for metabolic syndrome, irrespective of ethnicity.73 However, the NCEP-ATP III criteria for the diagnosis of abdominal obesity was noted to underestimate the prevalence of metabolic syndrome when applied to adult Asians. For example, Tan et al.74 showed that the optimal cut-off values to diagnose abdominal obesity, and by extension, metabolic syndrome, were >90 and >80 cm in males and females, respectively, among Asians. They had used secondary data on WC from adult male and female Chinese, Malay, and Asian Indians obtained from the 1998 Singapore National Health Survey and subjected the same to the receiver operating characteristics (ROC) analysis to derive this optimal WC in Asians.74 In recognition of ethnic differences, the WHO, together with the International Association for the Study of Obesity (IASO) and the International Obesity Task Force (IOTF), and the NCEP-ATP III have re-defined the cut-off values of WC for the diagnosis of abdominal obesity in metabolic syndrome among Asians as 90 and 80 cm for men and women, respectively.62,75 The International Diabetes Federation (IDF) also recognizes ethnic differences in body fat distribution. The IDF has issued a consensus statement on the sex- and ethnic-specific cut-off
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values for WC used in the definition of abdominal obesity as a component of metabolic syndrome.76 For Europids, the IDF set WC cut-off values of 94 cm or more and 80 cm or more for men and women, respectively. The cut-off value for adult women of Asian (South Asian, Chinese, and Japanese) origin is the same as for Europid women (>80 cm) but 4 cm lower for Asian men compared to Europid men (i.e., 90 vs 94 cm). The IDF recommended that European cut-off values should be applied to sub-Saharan Africans and Arabs (Middle-East and Eastern Mediterranean populations) citing lack of sufficient scientific data. Similarly, ethnic South and Central Americans should apply the same recommendations as for South Asians pending availability of specific data. Emerging data from sub-Saharan Africa, Middle East/ Eastern Mediterranean, and Central America suggest the need for the revision of the European cut-off values for WC recommended for use by the WHO, NCEP-ATP III, and IDF. In sub-Saharan Africa, several studies have shown that applying the IDF recommended cut-off values to identify levels at which WC identifies cardiometabolic risk inappropriate for black Africans.77–82 The CRIBSA study in Cape Town, South Africa, noted that WC cut-off values of 84 cm (men) and 94 cm (women) were optimal in identifying metabolic syndrome.77 Recently, Ekoru et al. published WC cut-off points of 81.2 and 81.0 cm for subSaharan African men and women, respectively, derived using the ROC analysis to identify the presence of two or more components of metabolic syndrome apart from WC.79 The cut-off values were obtained following analysis of data of over 21,000 participants drawn from 17 cross-sectional studies carried out between 1990 and 2014 in eight sub-Saharan countries.79 Another recently conducted cross-sectional study examined WC cut-off values that predict obesity using ROC analysis in apparently healthy adult Nigerians recruited from the six geopolitical zones in Nigeria.83 This study showed that the optimal WC cut-off values for identifying obesity (diagnosed as BMI 30 kg/m2) were >96 and >95 cm for men and women, respectively.83 It is pertinent to note that the studies emanating from sub-Saharan Africa are mostly cross-sectional studies with varying methodologies, thus limiting the inferential value of such studies. The observations, however, suggest that there may be a need for the WC cut-off values to be lowered in men and increased in women when compared to the currently used European cut-off recommended in the region.79 Further large-scale longitudinal studies with standardized methods are needed to provide more convincing evidence to support the call for ethnic-specific cut-off values in sub-Saharan Africa. Similarly, the appropriateness of the use of European cut-off values for WC and WHR to identify metabolic syndrome among ethnic groups from the Middle East and Eastern Mediterranean region is under scrutiny. Several cross-sectional studies from Arab countries have suggested different cut-off values, all of which vary from the recommended European cut-off values.84–88 For example, the proposed optimal WC cut-off values identifying metabolic syndrome for males and females, respectively, is: 92 and 87 cm in Saudi Arabia,84 99 and 97 cm in Iraq,85 99.5 and 91 cm in Qatar,86 89 and 91 cm in Iran,87 and 100.5 and 96.25 cm in Egypt.88 Applying the European cut-off values as recommended by IDF to identify metabolic syndrome led to an overestimation of the prevalence of abdominal obesity in Arab women in these studies. In all, there are strong indications that obesity-related cardiovascular and metabolic risks vary with ethnicity. Currently, aside from the WHtR, there are no universally acceptable cut-off values for the other anthropometric indices used to assess abdominal obesity. Although data on optimal cut-off values of anthropometric indices to predict obesity and its associated cardiometabolic risks are increasing globally, there is need to strengthen the evidence to support the calls to review the use of European cut-off values for WC among sub-Saharan Africans and Arabs. II. MECHANISMS OF OBESITY
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II. MECHANISMS OF OBESITY