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Diabetes Mellitus Prevention
Diabetes Mellitus Prevention Sabitha R Dasari, Reena Oza-Frank, and KM Venkat Narayan, Emory University, Atlanta, GA, USA Ó 2017 Elsevier Inc. All rights reserved. This article is reproduced from the previous edition, volume 2, pp. 146–152, Ó 2008, Elsevier Inc.
Introduction Diabetes is currently one of the most costly and burdensome chronic diseases, and it is a rapidly growing public health problem worldwide. The number of adults with diabetes in the world is expected to rise from 171 million in 2000 to 366 million in the year 2030, more than 75% of which will be in developing countries. The top three countries with the largest numbers of individuals with diabetes are India, China, and the United States, where the disease is a major cause of morbidity and mortality and contributes substantially to overall health-care costs (Wild et al., 2004). Diabetes mellitus is classified into two subtypes. Type 1 diabetes, formerly known as juvenile onset diabetes, comprises about 10% of cases, begins suddenly in childhood or adolescence, and always requires the treatment of insulin. Type 2 diabetes, formerly known as adult onset or non-insulin dependent diabetes mellitus (NIDDM), accounts for approximately 90% of all diagnosed cases of diabetes (CDC, 2005). Type 2 diabetes is also ranked as fifth among leading causes of death in the United States and is increasing in epidemic proportions both in the United States and throughout the world, especially in developing and newly industrialized countries. All forms of diabetes mellitus are characterized clinically by high circulating levels of blood glucose and abnormal levels of insulin. Type 1 diabetes begins rapidly due to failure of the insulin-producing beta cells of the pancreatic islets to maintain adequate levels of insulin needed for glucose to enter muscle and adipose tissue. Type 2 diabetes begins more gradually and proceeds through several stages. The initial problem is that muscle, adipose tissue, and the liver become less sensitive, or resistant, to the normal effects of circulating insulin. The body tries to compensate for high levels of circulating insulin by releasing greater amounts of insulin into the blood. As the pancreatic islet cells become exhausted and fail, however, insulin production decreases, leading to high blood glucose levels but low insulin levels. Type 2 diabetes is also characterized by high levels of free fatty acids, abnormal lipoprotein patterns, and long-term complications of vision loss, kidney dysfunction, nerve dysfunction, and increased risk of heart disease, stroke, and peripheral vascular disease. About one-third of the approximately 21 million people with diabetes in the United States have not yet been diagnosed. In addition to those who meet the clinical definition of diabetes, the American Diabetes Association (ADA) estimates that another 54 million Americans have prediabetes, defined as having blood glucose levels that are higher than normal but not high enough for a diagnosis of diabetes (Table 1). The clinical gradations of disease are discussed in greater detail later in the article. The risk factors for type 2 diabetes can be divided into those that are modifiable (obesity, physical inactivity, unhealthy diet, etc.) and those that are not (age, gender, family history, race or ethnicity, history of gestational diabetes, etc.). Inherited genes
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affect an individual’s propensity to gain weight or to develop insulin resistance or diabetes at a given level of adiposity. Hereditary factors do not, however, explain the rapid temporal increase in the prevalence of obesity and type 2 diabetes that are now occurring worldwide. The global increase in type 2 diabetes is caused by the extraordinary increase in overweight and obesity over the last 30 years (refer to other articles recommended at the end of this one). This in turn is caused by increased caloric consumption and sedentary lifestyles (Knowler et al., 1995). Although effective therapies are available to treat diabetes and reduce its complications, once diabetes develops it is challenging, costly, and burdensome to treat. Considering the severity of illness, low quality of life, and health-care costs associated with diabetes, primary prevention of type 2 diabetes is needed. Results of several recent clinical trials have shown that lifestyle interventions with diet and exercise may prevent or delay the development of diabetes in high-risk populations. This article reviews data from observational studies to identify the link between specific lifestyle behaviors and the incidence of diabetes, reviews evidence from clinical trials that show the effect of lifestyle interventions (diet or exercise) on prevention of diabetes, discusses reasons for the initiation of prevention programs, points out ways to identify high-risk groups for diabetes prevention, and discusses the challenges involved in implementation of these lifestyle interventions in communities and the potential mechanisms to overcome them.
Observational Studies of Modifiable Risk Factors Observational studies point to several potentially modifiable factors in the etiology of diabetes. The Nurses’ Health Study (Hu et al., 2001) found that 91% of the cases of diabetes could be attributed to just five variables, all of which were modifiable through lifestyle changes. These factors included obesity, physical inactivity, unhealthy diet, smoking, and alcohol consumption. Observational studies on these factors have been reviewed in detail elsewhere (Steyn et al., 2004). Bodyweight and weight gain have consistently been shown to be the strongest modifiable risk factors for diabetes (Knowler et al., 1995). Findings from the Ford et al. (1997) cohort study
Table 1
Criteria for diagnosis of prediabetes and diabetes Plasma glucose levels (mg dl1)
Condition
FPG
Diabetes Pre-diabetes Normal
2:126 2:110–<126 <110
OGTT and/or and/or and
2:200 2:140–<200 <140
FPG, fasting plasma glucose test; OGTT, oral glucose tolerance test.
International Encyclopedia of Public Health, 2nd edition, Volume 2
http://dx.doi.org/10.1016/B978-0-12-803678-5.00107-7
Diabetes Mellitus Prevention
showed that in a representative sample of the U.S. population, each unit increase in body mass index (BMI) was associated with a 12% increased risk of type 2 diabetes. Compared with persons with a BMI <22 kg m2, those with BMI 25– 27 kg m2 (considered overweight by current U.S. standards) had 2.75 times the risk of developing diabetes, and those with BMI of 31–32.9 kg m2 (considered obese by current U.S. standards) had a sevenfold increased risk. Compared to whites in the United States (CDC, 2005), prevalence of type 2 diabetes is higher in African-Americans, Asian-Americans and Pacific Islanders, Hispanic Americans, and Native Americans. Higher rates of type 2 diabetes in African-American women compared to white women have been shown to be attributable to higher prevalence of obesity. Asian populations (Filipinos, Japanese, Chinese, and South Asians) with body size similar to whites exhibit higher prevalence of type 2 diabetes. Studies have shown that this may be due to higher levels of visceral adipose tissue at lower BMI levels in these subgroups. The World Health Organization (2004) used this evidence to lower the recommended normal BMI level of Asians to S:23 kg m2 instead of the U.S. standard of S:25 kg m2. Physical activity is a key intervention for long-term weight maintenance and is thus crucial to lifestyle-based diabetes prevention. Even without weight loss, and regardless of BMI, physical activity may reduce diabetes risk (Schulze and Hu, 2005). In addition, when overweight or obese individuals engage in aerobic exercise, modest weight loss results independent of caloric reduction through dieting. Several studies have shown a dose–response decline in diabetes incidence across increasing levels of physical activity, with the largest decreases seen between sedentary individuals and moderately active individuals. Based on this evidence, as well as evidence from other studies showing benefits of physical activity, the Centers for Disease Control and Prevention and the American College of Sports Medicine recommend that healthy individuals engage in moderate intensity activity 2:30 min on 2:5 days per week or vigorous intensity activity 2:20 min on 2:3 days per week. Overall, pattern of a ‘Western’ diet (characterized by high consumption of red meat, processed meat, high-fat dairy products, sweets, and desserts) has been associated with increased risk of diabetes independent of BMI, physical activity, age, or family history; whereas a ‘prudent’ diet (characterized by higher consumption of vegetables, fruit, fish, poultry, and whole grains) has been associated with a reduced risk. The components of these dietary patterns have been studied individually. Diets composed of a high percentage of calories from fat may contribute to weight gain and development of obesity, but the results are mixed. There is more consistency in the literature, however, on the association of specific types of fat in the diet on diabetes risk. Higher levels of polyunsaturated fat have been associated with a lower risk of diabetes. The deleterious effects of saturated fats on cardiovascular disease risk are well documented, as are the effects of trans fats (Schulze and Hu, 2005). Similarly, diets which are low in calorie and high in fiber have been shown to reduce the risk of diabetes. Other dietary components with evidence of lowered risk of diabetes are consumption of low-fat dairy products and moderate alcohol consumption (Steyn et al., 2004). Unfortunately, inconsistency across studies of dietary factors has delayed a consensus on precisely which factors
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reduce the risk of diabetes. In addition, it remains unclear whether dietary factors work primarily to enhance weight maintenance or to lower diabetes incidence directly. One limitation to studying the relationship between specific dietary components and diabetes risk is that few people consume specific types of fats or carbohydrates in isolation, and thus dietary components may be confounded by other components. Also, an intrinsic limitation to observational studies is healthy-behavior bias in that the dietary factors may be confounded by another health-promoting behavior that was unmeasured. Despite difficulty in measuring the relationship between dietary factors and risk of diabetes, evidence from observational studies provided the scientific rationale to conduct clinical trials of diabetes prevention and to develop testable interventions.
Clinical Trials of Modifiable Risk Factors Since obesity, physical inactivity, and unhealthy diets have been identified as modifiable risk factors for type 2 diabetes, many studies have assessed the effect of lifestyle modification with diet or exercise or both on diabetes prevention. The results of these studies have shown that intensive lifestyle interventions, primarily in patients with impaired glucose tolerance (IGT; 2-h-post-75 g load plasma glucose level (2-h OGTT) of 140–199 mg dl1 (7.8–11.1 mmol l1)) or impaired fasting glucose (IFG; fasting glucose levels of 110–125 mg dl1 (5.6– 6.9 mmol l1)) may prevent or delay onset of type 2 diabetes. Characteristics and results of nine randomized controlled trials that assessed efficacy of lifestyle changes to prevent type 2 diabetes are shown in Table 2, and outcomes of some of these studies are discussed in this section. In the Finnish Diabetes Prevention Study (FDPS) (Lindstrom et al., 2003), 522 middle-aged (mean age 55 years), overweight (mean BMI 31 kg m2) subjects with impaired glucose tolerance were randomized to either a usual care control group or an intensive lifestyle intervention group. The subjects in the intervention group received individualized dietary counseling from a nutritionist, were offered circuit-type resistance training sessions, and were advised to increase overall physical activity. The control group received general dietary and exercise advice at baseline and had annual physician’s examinations. After 1 and 3 years, weight reductions were 4.5 and 3.5 kg in the intervention group and 1.0 and 0.9 kg in the control group, respectively. During the first 3 years of the study, the cumulative incidence of diabetes was significantly different between the two groups: 9% in the intervention group compared to 20% in the control group (p ¼ 0.0001), a 58% difference. The number of people needed to be treated to prevent one case of type 2 diabetes by lifestyle intervention was 22 for 1 year. The intensive lifestyle intervention produced long-term beneficial changes in diet, physical activity, and clinical and biochemical parameters and reduced diabetes risk. In the extended follow-up of the Finnish Diabetes Prevention Study (Lindstrom et al., 2006), the extent to which the originally achieved lifestyle changes and risk reduction would remain after discontinuation of active counseling was assessed. After a median 4 years of active intervention period, participants who were still free of diabetes were followed up for a further
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Table 2 Characteristics and results of clinical trials that assessed effect of lifestyle interventions with diet and/or exercise on type 2 diabetes prevention Type of intervention Study author (year)
Intervention type (N)
Knowler et al. (2002) DPP Lindstrom et al. (2003) Finnish DPS
Intensive lifestyle Standard lifestyle intervention (1079) advice (1082) Individual dietary General diet and session and exercise exercise advice training (265) (257) Diet and exercise (126) General health advice (133) Lifestyle modification Standard health care (133) advice (136) Intensive lifestyle Standard lifestyle intervention (102) advice (356) Intensive lifestyle General advice (32) intervention (37) New dietary education Regular diet (87) (86) Intensive diet and Routine diet exercise advice advice (100) (100) Endurance exercise for Stretching exercise 1 h three times three times a week a week þ AHA step 2 þ AHA step 1 diet diet (32) (32)
Li et al. (2002) Da Qing study Ramachandran et al. (2006) IDPP Kosaka et al. (2005) Oldroyd et al. (2005) UK Watanabe et al. (2004) Wein et al. (1999)
Liao et al. (2002)
Control group (N)
Weight change Relative risk (95% CI)
Intervention group
Control group
NNT a
Follow-up
0.42 (0.34–0.52)
0.23 kg (<0.5 lb) 0.9 kg
7
3 years
0.46 (0.3–0.7)
5.45 kg (12 lb) 3.5 kg
9
3 years
0.56 (0.40–0.80)
1.55 kg
3.33 kg
5
6 years
0.72 (0.63–0.80)
þ 0.15 kg
þ 0.5 kg
6
3 years
0.33 (0.1–1.01)
2.18 kg
0.39 kg
16
4 years
0.76 (0.31–1.85)
1.8 kg
þ1.5 kg
17
2 years
0.51 (0.13–1.96)
–
–
29
1 year
0.86 (0.30–2.46)
–
–
–
4.25 years
0.5 (0.05–5.24)
1.8 0.5
þ0.7 0.6
29
2 years
a
Number needed to be treated to prevent one case of type 2 diabetes in x (follow-up) years.
median of 3 years, with median total follow-up of 7 years. Diabetes incidence, bodyweight, physical activity, and dietary intakes of fat, saturated fat, and fiber were measured. During the total follow-up, the incidence of type 2 diabetes was 4.3 and 7.4 per 100 person-years in the intervention and control groups, respectively (p ¼ 0.0001), indicating a 43% reduction in relative risk. Beneficial lifestyle changes achieved by participants in the intervention group were maintained after the discontinuation of the intervention, and the corresponding incidence rates during the post-intervention follow-up were 4.6 and 7.2 per 100 person-years (p ¼ 0.0401), indicating a 36% risk reduction of diabetes. The Diabetes Prevention Program (DPP) (Knowler et al., 2002) was the largest and most diverse randomized controlled trial and was conducted in the United States. It took place in 27 clinical centers and assessed the effect of lifestyle or pharmacological intervention on diabetes. A total of 3819 men and women with elevated fasting and post-load plasma glucose were randomly assigned to one of the four groups: intensive lifestyle intervention, metformin with standard lifestyle advice, troglitazone with standard lifestyle intervention, and a control group who received placebo and standard lifestyle advice. Because of concern regarding its liver toxicity, the troglitazone arm was discontinued in June 1998. The mean age of participants was 51 years and mean BMI was 34 kg m2. The average follow-up was 2.8 years. The incidence of diabetes was 11.0, 7.8, and 4.8 cases per 100 person-years in the placebo, metformin, and lifestyle groups, respectively. The lifestyle intervention reduced the incidence by 58% (95% confidence interval, 48–66%) and metformin
by 31% (95% confidence interval, 17–43%), as compared with placebo; the lifestyle intervention was significantly more effective than metformin. To prevent one case of diabetes during a period of 3 years, 7 persons would have to participate in the lifestyle-intervention program for 3 years. The average weight loss was 5.45 kg (12 lb) for the intensive lifestyle intervention group and 0.23 kg (<0.5 lb) for the placebo group at 3 years of follow-up. A population-based screening study (Li et al., 2002) in Da Qing, China, was undertaken over a longer intervention period (6 years) than the FDPS or the DPP. The Da Qing Study differed from the FDPS and the DPP in that participants with IGT were randomized by group, rather than as individuals, into a control group or into one of three interventions – diet only, exercise only, or diet and exercise – in order to test the effectiveness of diet and exercise separately. The cumulative incidence of diabetes after 6 years was 67% in the control group, 43% in the diet group, 41% in the exercise group, and 46% in the diet plus exercise group. All the groups differed significantly from the control group (p < 0.05). Results from the above studies provide evidence that lifestyle interventions with diet and/or exercise are not only more effective than medications for diabetes prevention but also provide benefits related to weight loss, an improved diet, and beneficial effects on cardiovascular risk profile. These randomized controlled trials demonstrated that weight loss achieved by an increase in physical activity and dietary changes, including reduction in total and saturated fat and increased dietary fiber, can reduce the incidence of diabetes (Knowler et al., 2002).
Diabetes Mellitus Prevention
Rationale for Diabetes Prevention There are several reasons to justify initiating a program to prevent diabetes (ADA, 2002). First, diabetes is an important health problem. Second, several risk factors for diabetes have been identified. Incidence of diabetes is strongly related to the hyperglycemic states IFG and IGT. Although there is evidence that other factors are independently associated with the development of diabetes, such as age, family history of diabetes, waist-to-hip ratio, BMI, blood pressure, and lipid levels, none taken singly is as good at discriminating who will progress to diabetes as measuring glucose levels. Third, tests to detect the IFG and IGT are safe, acceptable and predictive. Two tests meet this criterion: measurement of fasting plasma glucose (FPG) and the 2-h value in the oral glucose tolerance test (OGTT). Both are widely available and have few adverse consequences. A positive value in either is predictive of the development of diabetes. Fourth, the results of the clinical studies described above indicate that there are safe, effective, and reliable interventions to prevent or delay diabetes. Finally, studies have shown that early recognition and treatment of high-risk groups, especially with lifestyle interventions, would be cost effective because patients would be younger, complications would not have developed, and there would be less need for use of pharmacotherapy and other health-care resources in later years.
Target Population for Interventions The American Diabetes Association has defined ‘prediabetes’ as the state that occurs when a person’s blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes, referred to as impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG). In the United States, based on NHANES III, 17.1% of overweight adults aged 45–74 years had IGT, 11.9% had IFG, 22.6% had prediabetes, and 5.6% had both IGT and IFG. Based on these data, Benjamin et al. (2003) estimated that in the year 2000, 9.1 million overweight adults aged 45–74 had IGT, 5.8 million had IFG, 11.9 million had prediabetes, and 3.0 million had IGT and IFG. Similar but slightly lower average prevalence estimates of IGT and IFG were found in the DECODE study (2003) in Europe (13% IGT and 5.7% IFG), in the DECODE study (2000) of 11 different Asian populations (15% IGT and 8% IFG), and in the Australian Diabetes, Obesity, and Lifestyle study (2002) in Australia (13% IGT and 7.4% IFG). Subjects with IGT and/or IFG (prediabetes) are at high risk for progression to diabetes and have been the target for preventive strategies in most clinical studies thus far. In the Hoorn study (de Vegt et al., 2001), risk for conversion to diabetes during 6.5 years of follow-up was about seven to eight times as high among people with IGT (57.9/1000 person-years) or impaired fasting glucose (51.4/1000 person-years) as among people with normoglycemia (7/1000 person-years). The combination of IFG and IGT yielded an incidence density for the conversion to diabetes more than 16 times the normoglycemic rate (112.2/1000 person-years). Although only 8% of
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people in the Hoorn Study had IGT, 40% incidence diabetes cases were attributable to IGT. Similarly, 10% had IFG, but 42% of diabetes cases were attributable to IFG. Although risk of conversion to diabetes is equivalent for IGT and IFG, these two abnormalities overlap by only 20–25%. Since all people who develop diabetes go through prediabetes (although the length of this phase may vary), effectively delivering preventive intervention programs to people with prediabetes (IGT and/or IFG) will ensure that most, if not all, future cases of diabetes are targeted.
Pre-Screening Questionnaires/Tests Several research groups have designed simple, inexpensive tools that attempt to identify individuals at high risk for type 2 diabetes. These tools are generally multivariate riskassessment questionnaires that aim to limit the proportion of the population requiring a blood glucose test. These questionnaires seem to perform well in identifying undiagnosed diabetes only when applied to the population for which it is designed. Rathmann et al. (2005) reviewed the performance of the Rotterdam Diabetes Study, Cambridge Risk Score, San Antonio Heart Study, and Finnish Diabetes Risk Score in identifying diabetes among 1353 German participants. The accuracy was only 61–67%; furthermore, inclusion of FPG measurement to the San Antonio Heart Study score improved the accuracy to 90%, which was not significantly different from that obtained by using FPG alone. Comparison of these four risk assessment scores revealed that questionnaires have low validity when applied to a new population, which was mainly due to differences in population characteristics. Another risk score involving simple, non-biochemical measurements was developed and tested in an urban population in India and also evaluated among migrant Indians living in the UK. The sensitivity and specificity of this score were considerably different among people from India living in the UK compared with those living in India (Ramachandran et al., 2005). Thus Diabetes Risk Score questionnaires generally have low accuracy and seem to be population-specific and inadequate for identifying individuals with impaired glucose tolerance and/or impaired FPG levels. So, we need an inexpensive, easy, standardized, reliable, and direct test of glycemia itself to identify high-risk populations.
Screening Tests ADA recommends using FPG test for diabetes screening; the WHO recommends use of 2-h OGTT for screening. The recommended cutoff values of FPG and 2-h OGTT to diagnose diabetes and prediabetes are shown in Table 1. The prevalence of IGT is 2–4 times higher than IFG, and these two glucose abnormalities overlap by only 20–25%. In the United States, Harris et al. (1997) reported that some individuals with a normal FPG level will have IGT or diabetes if a 2-h OGTT is performed, but fewer people with a normal 2-h OGTT will have IFG or diabetes if an FPG test alone is done. With the use of fasting glucose test (FPG) alone as a screening test, a fairly
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large group of people at high risk of developing diabetes will not be identified because individuals who have isolated post load hyperglycemia will have normal fasting glucose levels and can only be identified by using a 2-h OGTT. Thus, using the current definitions of IFG and IGT, the 2-h OGTT appears to identify more people who have impaired glucose homeostasis and thus, more people who will progress to diabetes. However, it has been suggested that if the cut-off point for FPG were lowered to 100 mg dl1, the FPG and 2-h OGTT would have similar sensitivity and positive predictive values, although it should be noted that they would not necessarily include the same individuals. For all the above reasons, the FPG test and/or 2-h OGTT can be used to screen for identifying a high-risk population for prevention. Regarding the tests themselves, the FPG test is more convenient to patients, more reproducible, less costly, and easier to administer than the 2-h OGTT. Opportunistic screening (i.e., screening during routine encounters with the health-care system) is the most cost-effective way to find individuals at risk for diabetes.
American Diabetes Association Recommendations The ADA issued recommendations (ADA, 2004) for prevention of diabetes which includes advice on who to screen, how to screen, and an intervention strategy: l
Men and women 2:45 years of age are candidates for screening to detect IFG or IGT (prediabetes), particularly those with a BMI 2:25 kg m2. Screening should be considered in younger persons with a BMI 2:25 kg m2 who have one of the following risk factors: a family history of diabetes, history of gestational diabetes or a baby weighing >4.1 kg (>9 lb), race other than Caucasian, dyslipidemia, or hypertension. In persons with normoglycemia, rescreening at 3-year intervals is reasonable. l Screening should be carried out as part of a health-care office visit. Either fasting plasma glucose (FPG) or a 2-hpost-75 g-load (2-h OGTT) oral glucose tolerance is appropriate, and a positive test result should be confirmed on another day. l Patients with IFG or IGT should be given counseling on weight loss as well as instructions for increasing physical activity. Follow-up counseling appears important for success. Monitoring for the development of diabetes should be performed every 1–2 years.
Practical Aspects of Lifestyle Modification Because overweight and obesity are strong modifiable risk factors for development of diabetes, they tend to be the main target of many lifestyle modifications for diabetes prevention. Weight gain occurs when energy intake exceeds energy expenditure, and by decreasing energy intake, weight loss should occur. To decrease caloric intake, it is recommended to follow a moderate decrease in caloric intake (500– 1000 calories/day) to facilitate a slow, progressive weight loss. The specific amount of caloric deficit should be
individually tailored to fit the individual’s needs and maximize adherence to the plan. An Institute of Medicine report concluded that getting nutritional therapy is worth the cost because management and prevention of disease through nutrition therapy can help cut health-care costs in the long term. A registered dietitian is typically chosen to dispense this advice; however, insurance companies vary in the reimbursement schemes for this service. Although the lifestyle approaches used in the nine studies reviewed in this chapter vary slightly, they all contain a diet component to facilitate weight loss. Each study, at different degrees, was successful in showing that regardless of the type of intervention; prevention of diabetes is possible through lifestyle modification. Despite this commonality among interventions, long-term adherence to lifestyle interventions and feasibility in a nontrial setting remain potentially limiting factors to widespread implementation.
Conclusion The results of the prevention studies mentioned above showed that lifestyle interventions with diet and/or exercise are effective for prevention or delay of type 2 diabetes, especially in high-risk populations like those with prediabetes. These lifestyle interventions not only have been shown to prevent or delay diabetes but also have shown benefits related to weight loss, physical activity, an improved diet, and beneficial effects on cardiovascular risk profile. In addition, data (Herman et al., 2005) also indicate that lifestyle interventions to prevent diabetes are highly cost effective and improve quality of life, especially if delivered at the level of primary care. Furthermore, identification of IGT and/or IFG will also provide the opportunity to address other cardiovascular risk factors (i.e., high blood pressure, dyslipidemia), which are prevalent in these groups, early. So health-care providers should urge all overweight and/or sedentary individuals to adopt lifestyle changes, and such recommendations should be made at every opportunity. Based on the strength of available evidence regarding diet and lifestyle in the prevention of type 2 diabetes, it is recommended to maintain a normal weight status in the lower BMI range (BMI 21–23 kg m2) and engage in regular physical activity throughout adulthood, avoid abdominal obesity, and limit saturated fat intake to less than 7% and total fat intake to less than 30% of total energy intake (Steyn et al., 2004). Societal factors such as the increased availability of fast foods, increased dependence on automobiles, and other unhealthy social developments are making healthy lifestyles difficult. Although practical aspects of delivering and maintaining long-term changes in lifestyle are challenging, several strategies and tools to overcome these challenges are available. Primary prevention of diabetes is both realistic and necessary.
See also: Cholesterol and Lipids; Diabetes Mellitus, Epidemiology; International Dietary Guidelines; Obesity/ Overweight: Health Consequences; Overweight and Obesity: Prevention and Weight Management; Physical Activity and Health; Principles: Mental Health Resources and Services.
Diabetes Mellitus Prevention
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Introduction Diabetes is currently one of the most costly and burdensome chronic diseases, and it is a rapidly growing public health problem worldwide. The number of adults with diabetes in the world is expected to rise from 171 million in 2000 to 366 million in the year 2030, more than 75% of which will be in developing countries. The top three countries with the largest numbers of individuals with diabetes are India, China, and the United States, where the disease is a major cause of morbidity and mortality and contributes substantially to overall health-care costs (Wild et al., 2004). Diabetes mellitus is classified into two subtypes. Type 1 diabetes, formerly known as juvenile onset diabetes, comprises about 10% of cases, begins suddenly in childhood or adolescence, and always requires the treatment of insulin. Type 2 diabetes, formerly known as adult onset or non-insulin dependent diabetes mellitus (NIDDM), accounts for approximately 90% of all diagnosed cases of diabetes (CDC, 2005). Type 2 diabetes is also ranked as fifth among leading causes of death in the United States and is increasing in epidemic proportions both in the United States and throughout the world, especially in developing and newly industrialized countries. All forms of diabetes mellitus are characterized clinically by high circulating levels of blood glucose and abnormal levels of insulin. Type 1 diabetes begins rapidly due to failure of the insulin-producing beta cells of the pancreatic islets to maintain adequate levels of insulin needed for glucose to enter muscle and adipose tissue. Type 2 diabetes begins more gradually and proceeds through several stages. The initial problem is that muscle, adipose tissue, and the liver become less sensitive, or resistant, to the normal effects of circulating insulin. The body tries to compensate for high levels of circulating insulin by releasing greater amounts of insulin into the blood. As the pancreatic islet cells become exhausted and fail, however, insulin production decreases, leading to high blood glucose levels but low insulin levels. Type 2 diabetes is also characterized by high levels of free fatty acids, abnormal lipoprotein patterns, and long-term complications of vision loss, kidney dysfunction, nerve dysfunction, and increased risk of heart disease, stroke, and peripheral vascular disease. About one-third of the approximately 21 million people with diabetes in the United States have not yet been diagnosed. In addition to those who meet the clinical definition of diabetes, the American Diabetes Association (ADA) estimates that another 54 million Americans have prediabetes, defined as having blood glucose levels that are higher than normal but not high enough for a diagnosis of diabetes (Table 1). The clinical gradations of disease are discussed in greater detail later in the article. The risk factors for type 2 diabetes can be divided into those that are modifiable (obesity, physical inactivity, unhealthy diet, etc.) and those that are not (age, gender, family history, race or ethnicity, history of gestational diabetes, etc.). Inherited genes
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affect an individual’s propensity to gain weight or to develop insulin resistance or diabetes at a given level of adiposity. Hereditary factors do not, however, explain the rapid temporal increase in the prevalence of obesity and type 2 diabetes that are now occurring worldwide. The global increase in type 2 diabetes is caused by the extraordinary increase in overweight and obesity over the last 30 years (refer to other articles recommended at the end of this one). This in turn is caused by increased caloric consumption and sedentary lifestyles (Knowler et al., 1995). Although effective therapies are available to treat diabetes and reduce its complications, once diabetes develops it is challenging, costly, and burdensome to treat. Considering the severity of illness, low quality of life, and health-care costs associated with diabetes, primary prevention of type 2 diabetes is needed. Results of several recent clinical trials have shown that lifestyle interventions with diet and exercise may prevent or delay the development of diabetes in high-risk populations. This article reviews data from observational studies to identify the link between specific lifestyle behaviors and the incidence of diabetes, reviews evidence from clinical trials that show the effect of lifestyle interventions (diet or exercise) on prevention of diabetes, discusses reasons for the initiation of prevention programs, points out ways to identify high-risk groups for diabetes prevention, and discusses the challenges involved in implementation of these lifestyle interventions in communities and the potential mechanisms to overcome them.
Observational Studies of Modifiable Risk Factors Observational studies point to several potentially modifiable factors in the etiology of diabetes. The Nurses’ Health Study (Hu et al., 2001) found that 91% of the cases of diabetes could be attributed to just five variables, all of which were modifiable through lifestyle changes. These factors included obesity, physical inactivity, unhealthy diet, smoking, and alcohol consumption. Observational studies on these factors have been reviewed in detail elsewhere (Steyn et al., 2004). Bodyweight and weight gain have consistently been shown to be the strongest modifiable risk factors for diabetes (Knowler et al., 1995). Findings from the Ford et al. (1997) cohort study
Table 1
Criteria for diagnosis of prediabetes and diabetes Plasma glucose levels (mg dl1)
Condition
FPG
Diabetes Pre-diabetes Normal
2:126 2:110–<126 <110
OGTT and/or and/or and
2:200 2:140–<200 <140
FPG, fasting plasma glucose test; OGTT, oral glucose tolerance test.
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showed that in a representative sample of the U.S. population, each unit increase in body mass index (BMI) was associated with a 12% increased risk of type 2 diabetes. Compared with persons with a BMI <22 kg m2, those with BMI 25– 27 kg m2 (considered overweight by current U.S. standards) had 2.75 times the risk of developing diabetes, and those with BMI of 31–32.9 kg m2 (considered obese by current U.S. standards) had a sevenfold increased risk. Compared to whites in the United States (CDC, 2005), prevalence of type 2 diabetes is higher in African-Americans, Asian-Americans and Pacific Islanders, Hispanic Americans, and Native Americans. Higher rates of type 2 diabetes in African-American women compared to white women have been shown to be attributable to higher prevalence of obesity. Asian populations (Filipinos, Japanese, Chinese, and South Asians) with body size similar to whites exhibit higher prevalence of type 2 diabetes. Studies have shown that this may be due to higher levels of visceral adipose tissue at lower BMI levels in these subgroups. The World Health Organization (2004) used this evidence to lower the recommended normal BMI level of Asians to S:23 kg m2 instead of the U.S. standard of S:25 kg m2. Physical activity is a key intervention for long-term weight maintenance and is thus crucial to lifestyle-based diabetes prevention. Even without weight loss, and regardless of BMI, physical activity may reduce diabetes risk (Schulze and Hu, 2005). In addition, when overweight or obese individuals engage in aerobic exercise, modest weight loss results independent of caloric reduction through dieting. Several studies have shown a dose–response decline in diabetes incidence across increasing levels of physical activity, with the largest decreases seen between sedentary individuals and moderately active individuals. Based on this evidence, as well as evidence from other studies showing benefits of physical activity, the Centers for Disease Control and Prevention and the American College of Sports Medicine recommend that healthy individuals engage in moderate intensity activity 2:30 min on 2:5 days per week or vigorous intensity activity 2:20 min on 2:3 days per week. Overall, pattern of a ‘Western’ diet (characterized by high consumption of red meat, processed meat, high-fat dairy products, sweets, and desserts) has been associated with increased risk of diabetes independent of BMI, physical activity, age, or family history; whereas a ‘prudent’ diet (characterized by higher consumption of vegetables, fruit, fish, poultry, and whole grains) has been associated with a reduced risk. The components of these dietary patterns have been studied individually. Diets composed of a high percentage of calories from fat may contribute to weight gain and development of obesity, but the results are mixed. There is more consistency in the literature, however, on the association of specific types of fat in the diet on diabetes risk. Higher levels of polyunsaturated fat have been associated with a lower risk of diabetes. The deleterious effects of saturated fats on cardiovascular disease risk are well documented, as are the effects of trans fats (Schulze and Hu, 2005). Similarly, diets which are low in calorie and high in fiber have been shown to reduce the risk of diabetes. Other dietary components with evidence of lowered risk of diabetes are consumption of low-fat dairy products and moderate alcohol consumption (Steyn et al., 2004). Unfortunately, inconsistency across studies of dietary factors has delayed a consensus on precisely which factors
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reduce the risk of diabetes. In addition, it remains unclear whether dietary factors work primarily to enhance weight maintenance or to lower diabetes incidence directly. One limitation to studying the relationship between specific dietary components and diabetes risk is that few people consume specific types of fats or carbohydrates in isolation, and thus dietary components may be confounded by other components. Also, an intrinsic limitation to observational studies is healthy-behavior bias in that the dietary factors may be confounded by another health-promoting behavior that was unmeasured. Despite difficulty in measuring the relationship between dietary factors and risk of diabetes, evidence from observational studies provided the scientific rationale to conduct clinical trials of diabetes prevention and to develop testable interventions.
Clinical Trials of Modifiable Risk Factors Since obesity, physical inactivity, and unhealthy diets have been identified as modifiable risk factors for type 2 diabetes, many studies have assessed the effect of lifestyle modification with diet or exercise or both on diabetes prevention. The results of these studies have shown that intensive lifestyle interventions, primarily in patients with impaired glucose tolerance (IGT; 2-h-post-75 g load plasma glucose level (2-h OGTT) of 140–199 mg dl1 (7.8–11.1 mmol l1)) or impaired fasting glucose (IFG; fasting glucose levels of 110–125 mg dl1 (5.6– 6.9 mmol l1)) may prevent or delay onset of type 2 diabetes. Characteristics and results of nine randomized controlled trials that assessed efficacy of lifestyle changes to prevent type 2 diabetes are shown in Table 2, and outcomes of some of these studies are discussed in this section. In the Finnish Diabetes Prevention Study (FDPS) (Lindstrom et al., 2003), 522 middle-aged (mean age 55 years), overweight (mean BMI 31 kg m2) subjects with impaired glucose tolerance were randomized to either a usual care control group or an intensive lifestyle intervention group. The subjects in the intervention group received individualized dietary counseling from a nutritionist, were offered circuit-type resistance training sessions, and were advised to increase overall physical activity. The control group received general dietary and exercise advice at baseline and had annual physician’s examinations. After 1 and 3 years, weight reductions were 4.5 and 3.5 kg in the intervention group and 1.0 and 0.9 kg in the control group, respectively. During the first 3 years of the study, the cumulative incidence of diabetes was significantly different between the two groups: 9% in the intervention group compared to 20% in the control group (p ¼ 0.0001), a 58% difference. The number of people needed to be treated to prevent one case of type 2 diabetes by lifestyle intervention was 22 for 1 year. The intensive lifestyle intervention produced long-term beneficial changes in diet, physical activity, and clinical and biochemical parameters and reduced diabetes risk. In the extended follow-up of the Finnish Diabetes Prevention Study (Lindstrom et al., 2006), the extent to which the originally achieved lifestyle changes and risk reduction would remain after discontinuation of active counseling was assessed. After a median 4 years of active intervention period, participants who were still free of diabetes were followed up for a further
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Table 2 Characteristics and results of clinical trials that assessed effect of lifestyle interventions with diet and/or exercise on type 2 diabetes prevention Type of intervention Study author (year)
Intervention type (N)
Knowler et al. (2002) DPP Lindstrom et al. (2003) Finnish DPS
Intensive lifestyle Standard lifestyle intervention (1079) advice (1082) Individual dietary General diet and session and exercise exercise advice training (265) (257) Diet and exercise (126) General health advice (133) Lifestyle modification Standard health care (133) advice (136) Intensive lifestyle Standard lifestyle intervention (102) advice (356) Intensive lifestyle General advice (32) intervention (37) New dietary education Regular diet (87) (86) Intensive diet and Routine diet exercise advice advice (100) (100) Endurance exercise for Stretching exercise 1 h three times three times a week a week þ AHA step 2 þ AHA step 1 diet diet (32) (32)
Li et al. (2002) Da Qing study Ramachandran et al. (2006) IDPP Kosaka et al. (2005) Oldroyd et al. (2005) UK Watanabe et al. (2004) Wein et al. (1999)
Liao et al. (2002)
Control group (N)
Weight change Relative risk (95% CI)
Intervention group
Control group
NNT a
Follow-up
0.42 (0.34–0.52)
0.23 kg (<0.5 lb) 0.9 kg
7
3 years
0.46 (0.3–0.7)
5.45 kg (12 lb) 3.5 kg
9
3 years
0.56 (0.40–0.80)
1.55 kg
3.33 kg
5
6 years
0.72 (0.63–0.80)
þ 0.15 kg
þ 0.5 kg
6
3 years
0.33 (0.1–1.01)
2.18 kg
0.39 kg
16
4 years
0.76 (0.31–1.85)
1.8 kg
þ1.5 kg
17
2 years
0.51 (0.13–1.96)
–
–
29
1 year
0.86 (0.30–2.46)
–
–
–
4.25 years
0.5 (0.05–5.24)
1.8 0.5
þ0.7 0.6
29
2 years
a
Number needed to be treated to prevent one case of type 2 diabetes in x (follow-up) years.
median of 3 years, with median total follow-up of 7 years. Diabetes incidence, bodyweight, physical activity, and dietary intakes of fat, saturated fat, and fiber were measured. During the total follow-up, the incidence of type 2 diabetes was 4.3 and 7.4 per 100 person-years in the intervention and control groups, respectively (p ¼ 0.0001), indicating a 43% reduction in relative risk. Beneficial lifestyle changes achieved by participants in the intervention group were maintained after the discontinuation of the intervention, and the corresponding incidence rates during the post-intervention follow-up were 4.6 and 7.2 per 100 person-years (p ¼ 0.0401), indicating a 36% risk reduction of diabetes. The Diabetes Prevention Program (DPP) (Knowler et al., 2002) was the largest and most diverse randomized controlled trial and was conducted in the United States. It took place in 27 clinical centers and assessed the effect of lifestyle or pharmacological intervention on diabetes. A total of 3819 men and women with elevated fasting and post-load plasma glucose were randomly assigned to one of the four groups: intensive lifestyle intervention, metformin with standard lifestyle advice, troglitazone with standard lifestyle intervention, and a control group who received placebo and standard lifestyle advice. Because of concern regarding its liver toxicity, the troglitazone arm was discontinued in June 1998. The mean age of participants was 51 years and mean BMI was 34 kg m2. The average follow-up was 2.8 years. The incidence of diabetes was 11.0, 7.8, and 4.8 cases per 100 person-years in the placebo, metformin, and lifestyle groups, respectively. The lifestyle intervention reduced the incidence by 58% (95% confidence interval, 48–66%) and metformin
by 31% (95% confidence interval, 17–43%), as compared with placebo; the lifestyle intervention was significantly more effective than metformin. To prevent one case of diabetes during a period of 3 years, 7 persons would have to participate in the lifestyle-intervention program for 3 years. The average weight loss was 5.45 kg (12 lb) for the intensive lifestyle intervention group and 0.23 kg (<0.5 lb) for the placebo group at 3 years of follow-up. A population-based screening study (Li et al., 2002) in Da Qing, China, was undertaken over a longer intervention period (6 years) than the FDPS or the DPP. The Da Qing Study differed from the FDPS and the DPP in that participants with IGT were randomized by group, rather than as individuals, into a control group or into one of three interventions – diet only, exercise only, or diet and exercise – in order to test the effectiveness of diet and exercise separately. The cumulative incidence of diabetes after 6 years was 67% in the control group, 43% in the diet group, 41% in the exercise group, and 46% in the diet plus exercise group. All the groups differed significantly from the control group (p < 0.05). Results from the above studies provide evidence that lifestyle interventions with diet and/or exercise are not only more effective than medications for diabetes prevention but also provide benefits related to weight loss, an improved diet, and beneficial effects on cardiovascular risk profile. These randomized controlled trials demonstrated that weight loss achieved by an increase in physical activity and dietary changes, including reduction in total and saturated fat and increased dietary fiber, can reduce the incidence of diabetes (Knowler et al., 2002).
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Rationale for Diabetes Prevention There are several reasons to justify initiating a program to prevent diabetes (ADA, 2002). First, diabetes is an important health problem. Second, several risk factors for diabetes have been identified. Incidence of diabetes is strongly related to the hyperglycemic states IFG and IGT. Although there is evidence that other factors are independently associated with the development of diabetes, such as age, family history of diabetes, waist-to-hip ratio, BMI, blood pressure, and lipid levels, none taken singly is as good at discriminating who will progress to diabetes as measuring glucose levels. Third, tests to detect the IFG and IGT are safe, acceptable and predictive. Two tests meet this criterion: measurement of fasting plasma glucose (FPG) and the 2-h value in the oral glucose tolerance test (OGTT). Both are widely available and have few adverse consequences. A positive value in either is predictive of the development of diabetes. Fourth, the results of the clinical studies described above indicate that there are safe, effective, and reliable interventions to prevent or delay diabetes. Finally, studies have shown that early recognition and treatment of high-risk groups, especially with lifestyle interventions, would be cost effective because patients would be younger, complications would not have developed, and there would be less need for use of pharmacotherapy and other health-care resources in later years.
Target Population for Interventions The American Diabetes Association has defined ‘prediabetes’ as the state that occurs when a person’s blood glucose levels are higher than normal but not high enough for a diagnosis of diabetes, referred to as impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG). In the United States, based on NHANES III, 17.1% of overweight adults aged 45–74 years had IGT, 11.9% had IFG, 22.6% had prediabetes, and 5.6% had both IGT and IFG. Based on these data, Benjamin et al. (2003) estimated that in the year 2000, 9.1 million overweight adults aged 45–74 had IGT, 5.8 million had IFG, 11.9 million had prediabetes, and 3.0 million had IGT and IFG. Similar but slightly lower average prevalence estimates of IGT and IFG were found in the DECODE study (2003) in Europe (13% IGT and 5.7% IFG), in the DECODE study (2000) of 11 different Asian populations (15% IGT and 8% IFG), and in the Australian Diabetes, Obesity, and Lifestyle study (2002) in Australia (13% IGT and 7.4% IFG). Subjects with IGT and/or IFG (prediabetes) are at high risk for progression to diabetes and have been the target for preventive strategies in most clinical studies thus far. In the Hoorn study (de Vegt et al., 2001), risk for conversion to diabetes during 6.5 years of follow-up was about seven to eight times as high among people with IGT (57.9/1000 person-years) or impaired fasting glucose (51.4/1000 person-years) as among people with normoglycemia (7/1000 person-years). The combination of IFG and IGT yielded an incidence density for the conversion to diabetes more than 16 times the normoglycemic rate (112.2/1000 person-years). Although only 8% of
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people in the Hoorn Study had IGT, 40% incidence diabetes cases were attributable to IGT. Similarly, 10% had IFG, but 42% of diabetes cases were attributable to IFG. Although risk of conversion to diabetes is equivalent for IGT and IFG, these two abnormalities overlap by only 20–25%. Since all people who develop diabetes go through prediabetes (although the length of this phase may vary), effectively delivering preventive intervention programs to people with prediabetes (IGT and/or IFG) will ensure that most, if not all, future cases of diabetes are targeted.
Pre-Screening Questionnaires/Tests Several research groups have designed simple, inexpensive tools that attempt to identify individuals at high risk for type 2 diabetes. These tools are generally multivariate riskassessment questionnaires that aim to limit the proportion of the population requiring a blood glucose test. These questionnaires seem to perform well in identifying undiagnosed diabetes only when applied to the population for which it is designed. Rathmann et al. (2005) reviewed the performance of the Rotterdam Diabetes Study, Cambridge Risk Score, San Antonio Heart Study, and Finnish Diabetes Risk Score in identifying diabetes among 1353 German participants. The accuracy was only 61–67%; furthermore, inclusion of FPG measurement to the San Antonio Heart Study score improved the accuracy to 90%, which was not significantly different from that obtained by using FPG alone. Comparison of these four risk assessment scores revealed that questionnaires have low validity when applied to a new population, which was mainly due to differences in population characteristics. Another risk score involving simple, non-biochemical measurements was developed and tested in an urban population in India and also evaluated among migrant Indians living in the UK. The sensitivity and specificity of this score were considerably different among people from India living in the UK compared with those living in India (Ramachandran et al., 2005). Thus Diabetes Risk Score questionnaires generally have low accuracy and seem to be population-specific and inadequate for identifying individuals with impaired glucose tolerance and/or impaired FPG levels. So, we need an inexpensive, easy, standardized, reliable, and direct test of glycemia itself to identify high-risk populations.
Screening Tests ADA recommends using FPG test for diabetes screening; the WHO recommends use of 2-h OGTT for screening. The recommended cutoff values of FPG and 2-h OGTT to diagnose diabetes and prediabetes are shown in Table 1. The prevalence of IGT is 2–4 times higher than IFG, and these two glucose abnormalities overlap by only 20–25%. In the United States, Harris et al. (1997) reported that some individuals with a normal FPG level will have IGT or diabetes if a 2-h OGTT is performed, but fewer people with a normal 2-h OGTT will have IFG or diabetes if an FPG test alone is done. With the use of fasting glucose test (FPG) alone as a screening test, a fairly
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large group of people at high risk of developing diabetes will not be identified because individuals who have isolated post load hyperglycemia will have normal fasting glucose levels and can only be identified by using a 2-h OGTT. Thus, using the current definitions of IFG and IGT, the 2-h OGTT appears to identify more people who have impaired glucose homeostasis and thus, more people who will progress to diabetes. However, it has been suggested that if the cut-off point for FPG were lowered to 100 mg dl1, the FPG and 2-h OGTT would have similar sensitivity and positive predictive values, although it should be noted that they would not necessarily include the same individuals. For all the above reasons, the FPG test and/or 2-h OGTT can be used to screen for identifying a high-risk population for prevention. Regarding the tests themselves, the FPG test is more convenient to patients, more reproducible, less costly, and easier to administer than the 2-h OGTT. Opportunistic screening (i.e., screening during routine encounters with the health-care system) is the most cost-effective way to find individuals at risk for diabetes.
American Diabetes Association Recommendations The ADA issued recommendations (ADA, 2004) for prevention of diabetes which includes advice on who to screen, how to screen, and an intervention strategy: l
Men and women 2:45 years of age are candidates for screening to detect IFG or IGT (prediabetes), particularly those with a BMI 2:25 kg m2. Screening should be considered in younger persons with a BMI 2:25 kg m2 who have one of the following risk factors: a family history of diabetes, history of gestational diabetes or a baby weighing >4.1 kg (>9 lb), race other than Caucasian, dyslipidemia, or hypertension. In persons with normoglycemia, rescreening at 3-year intervals is reasonable. l Screening should be carried out as part of a health-care office visit. Either fasting plasma glucose (FPG) or a 2-hpost-75 g-load (2-h OGTT) oral glucose tolerance is appropriate, and a positive test result should be confirmed on another day. l Patients with IFG or IGT should be given counseling on weight loss as well as instructions for increasing physical activity. Follow-up counseling appears important for success. Monitoring for the development of diabetes should be performed every 1–2 years.
Practical Aspects of Lifestyle Modification Because overweight and obesity are strong modifiable risk factors for development of diabetes, they tend to be the main target of many lifestyle modifications for diabetes prevention. Weight gain occurs when energy intake exceeds energy expenditure, and by decreasing energy intake, weight loss should occur. To decrease caloric intake, it is recommended to follow a moderate decrease in caloric intake (500– 1000 calories/day) to facilitate a slow, progressive weight loss. The specific amount of caloric deficit should be
individually tailored to fit the individual’s needs and maximize adherence to the plan. An Institute of Medicine report concluded that getting nutritional therapy is worth the cost because management and prevention of disease through nutrition therapy can help cut health-care costs in the long term. A registered dietitian is typically chosen to dispense this advice; however, insurance companies vary in the reimbursement schemes for this service. Although the lifestyle approaches used in the nine studies reviewed in this chapter vary slightly, they all contain a diet component to facilitate weight loss. Each study, at different degrees, was successful in showing that regardless of the type of intervention; prevention of diabetes is possible through lifestyle modification. Despite this commonality among interventions, long-term adherence to lifestyle interventions and feasibility in a nontrial setting remain potentially limiting factors to widespread implementation.
Conclusion The results of the prevention studies mentioned above showed that lifestyle interventions with diet and/or exercise are effective for prevention or delay of type 2 diabetes, especially in high-risk populations like those with prediabetes. These lifestyle interventions not only have been shown to prevent or delay diabetes but also have shown benefits related to weight loss, physical activity, an improved diet, and beneficial effects on cardiovascular risk profile. In addition, data (Herman et al., 2005) also indicate that lifestyle interventions to prevent diabetes are highly cost effective and improve quality of life, especially if delivered at the level of primary care. Furthermore, identification of IGT and/or IFG will also provide the opportunity to address other cardiovascular risk factors (i.e., high blood pressure, dyslipidemia), which are prevalent in these groups, early. So health-care providers should urge all overweight and/or sedentary individuals to adopt lifestyle changes, and such recommendations should be made at every opportunity. Based on the strength of available evidence regarding diet and lifestyle in the prevention of type 2 diabetes, it is recommended to maintain a normal weight status in the lower BMI range (BMI 21–23 kg m2) and engage in regular physical activity throughout adulthood, avoid abdominal obesity, and limit saturated fat intake to less than 7% and total fat intake to less than 30% of total energy intake (Steyn et al., 2004). Societal factors such as the increased availability of fast foods, increased dependence on automobiles, and other unhealthy social developments are making healthy lifestyles difficult. Although practical aspects of delivering and maintaining long-term changes in lifestyle are challenging, several strategies and tools to overcome these challenges are available. Primary prevention of diabetes is both realistic and necessary.
See also: Cholesterol and Lipids; Diabetes Mellitus, Epidemiology; International Dietary Guidelines; Obesity/ Overweight: Health Consequences; Overweight and Obesity: Prevention and Weight Management; Physical Activity and Health; Principles: Mental Health Resources and Services.
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