- Email: [email protected]
Carbohydrates: how low can you go?
Comment
Carbohydrates: how low can you go? See Case Report page 958
In today’s Lancet, Tsuh-Yin Chen and colleagues1 describe a patient admitted to hospital for ketoacidosis presumably as a result of following the Atkins lowcarbohydrate diet. The Atkins diet can be appealing to overweight and obese individuals because it boasts good health and, most importantly, rapid weight loss without hunger in the first and most restrictive stage of the diet.2 This dangling carrot often provides the motivation needed to propel individuals to continue with a diet that they might otherwise quit within the first few days because of its significant restriction in food choices. While the rapid weight loss seems to be an obvious benefit of the Atkins diet, bigger questions remain: first, is the diet safe? And second, can this early success motivate individuals to maintain dietary changes for a lifetime? Low-carbohydrate diets for weight management are far from healthy, given their association with ketosis, constipation or diarrhoea, halitosis, headache, and general fatigue to name a few side-effects.1,3 These diets also increase the protein load to the kidneys and alter the acid balance of the body, which can result in loss of minerals from bone stores, thus compromising bone integrity.4 To date, no low-carbohydrate intervention trials have been of sufficient duration to investigate long-term effects of such dietary changes, and the effects of low-carbohydrate diets on intermediate endpoints, such as kidney enzymes and markers of bone metabolism, are equivocal. However, two 12-month intervention trials5,6 showed no significant difference in weight loss after 12 months between a low-carbohydrate diet and a traditional low-fat diet, although individuals randomised to the low-carbohydrate diet
lost significantly more weight at 6 months compared with the low-fat dieters. Teaching at-risk individuals how to manage their weight in ways that are healthy and can be maintained for a lifetime is of utmost importance. Traditional and healthy weight-control practices include increasing physical activity and modifying dietary patterns, such as increasing intakes of wholegrain products and fruit and vegetables.7,8 Many longitudinal epidemiological studies have shown significantly lower risk of cardiovascular disease,9 stroke,10 cancer,11 and other conditions associated with consumption of fruits, vegetables, and wholegrains; some of these foods are noticeably absent from the menu of low-carbohydrate diets.2 Overall, studies of weight loss undoubtedly show reduced risk of chronic diseases such as hypertension, diabetes, and risk factors for other metabolic conditions, but are we to assume that weight loss by any means will have similar benefits? Chen and colleagues will probably agree that lowcarbohydrate diets should not be recommended for weight loss.1 The American Dietetic Association’s position on weight control is that “successful weight management to improve overall health for adults requires a lifelong commitment to healthful lifestyle behaviors emphasizing sustainable and enjoyable eating practices and daily physical activity”.12 The table shows recommended servings from each food group for the Atkins diet and the 2005 Dietary Guidelines for Americans.13 Clearly, the Atkins diet is not nutritionally balanced. Special care needs to be taken when formulating the best prescription for weight loss, because people choosing to lose weight range from being marginally to
Food group
Atkins diet Induction (2 weeks to 6 months)
2005 US Dietary Guidelines (based on 2000 kcal diet)
Meat, poultry, fish, legumes, nuts Dairy Vegetables Fruit Grains Oils Drinks
Unlimited meat, poultry, eggs, and fish; no legumes or nuts 3–4 oz cheese; no other dairy foods 2 cups lettuce and 1 cup other vegetables (~20 g carbohydrate) None None Unlimited amount 64 fluid oz water No caffeinated drinks Recommended
5·5 oz 3 cups milk (or equivalent amount yoghurt or cheese) 2·5 cups 2 cups 6 oz (half wholegrain) 6 teaspoons No recommendation
Vitamin and mineral supplements
No recommendation
All cups are US cups.
Table: Daily recommended food intake according to Atkins diet and 2005 US dietary guidelines13
880
www.thelancet.com Vol 367 March 18, 2006
Comment
significantly overweight, and might have a wide range of disease risk factors with varying levels of severity. As researchers and clinicians, our most important criterion should be indisputable safety, and low-carbohydrate diets currently fall short of this benchmark. *Lyn M Steffen, Jennifer A Nettleton University of Minnesota School of Public Health, Division of Epidemiology and Community Health, Minneapolis, MN 55454, USA [email protected]
5 6
7 8
9
10
We declare that we have no conflict of interest. 1 2
3 4
Chen TY, Smith W, Rosenstock JL, Lessnau KD. A life-threatening complication of Atkins Diet. Lancet 2006: 367: 958. Astrup A, Larsen TM, Harper A. Atkins and other low-carbohydrate diets: hoax or an effective tool for weight loss? Lancet 2004; 364: 897–99. Freedman MR, King J, Kennedy E. Popular diets: a scientific review. Obes Res 2001; 9 (suppl 1): 1S–40. Metgas CC, Barth CA. Metabolic consequences of a high dietary–protein intake in adulthood: assessment of the available evidence. J Nutr 2000; 130: 886–89.
11
12
13
Foster GD, Wyatt HR, Hill JO, et al. A randomized trial of a lowcarbohydrate diet for obesity. N Engl J Med 2003; 348: 2082–90. Samaha FF, Iqbal N, Seshadri P, et al. A low-carbohydrate as compared with a low-fat diet in severe obesity. N Engl J Med 2003; 348: 2074–81. USDA. MyPyramid.gov: steps to a healthier you. http://www.mypyramid. gov/ (accessed Jan 12, 2005). Nutrition and Food Security Programme. Food-based dietary guidelines in the WHO European region. 2003: http://www.euro.who.int/ Document/E79832.pdf (accessed Jan 12, 2006). Steffen LM, Jacobs DR, Stevens J, Shahar E, Carithers T, Folsom AR. Associations of whole grain, refined grain, and fruit and vegetable consumption with all-cause mortality, incident coronary heart disease and ischemic stroke: the ARIC Study. Am J Clin Nutr 2003; 78: 383–90. Ness AR, Powles JW. Fruit and vegetables, and cardiovascular disease: a review. Int J Epidemiol 1997; 26: 1–13. Malin AS, Qi D, Shu XO, et al. Intake of fruits, vegetables and selected micronutrients in relation to the risk of breast cancer. Int J Cancer 2003; 105: 413–18. Cummings S, Parham ES, Strain GW. Position paper of the American Dietetic Association: weight management. J Am Diet Assoc 2002; 102: 1145–55. US Department of Health and Human Services, US Department of Agriculture. 2005 U.S. Dietary Guidelines for Americans. http:// www.health.gov/dietaryguidelines/dga2005/document/pdf/ dga2005.pdf (accessed Jan 11, 2006).
Systematic reviews: when is an update an update? Governments are investing heavily in the use of systematic reviews to inform health-care policy.1 The value of systematic reviews is best when they are kept up to date, since evidence is continually evolving as new research becomes available. For example, certain healthcare interventions currently known to be effective will be shown to be ineffective or harmful in the future, or vice versa.2 To ignore the emergence of new information might therefore undermine the validity of systematic reviews. Although many researchers have addressed several methodological issues of updating systematic reviews,2–6 none has provided a formal definition of what constitutes an update. The definition7 of “to update” means “to extend up to the present time” or “to include the latest information”. Without a formal definition, investigators and readers could have difficulties in determining whether or not any given systematic review has been updated. Furthermore, researchers who undertake surveys of updating practices or studies that deal with different methods of updating could perceive updating processes differently, leading to inconsistent assessments of how current any given systematic review is. These differences, in turn, will render current and future studies non-comparable. www.thelancet.com Vol 367 March 18, 2006
We believe that the introduction of a formal definition and explanation for this important construct is long overdue. We define an update of a systematic review as a discrete event with the aim to search for and identify new evidence to incorporate into a previously completed systematic review. The central and necessary element of an update is the effort to identify new evidence. We use “new evidence” broadly—evidence that has not been included in the previously completed review. For example, use of the search strategy (eg, MeSH terms, years searched) from the original review, but with an additional database (MEDLINE vs MEDLINE and EMBASE) to identify new evidence, is regarded as an update. Alternatively, updating could be initiated after a specific period of time has elapsed since the completion of the original systematic review, which allows for the identification of new evidence that has emerged during this time. Even if a search does not identify any new evidence relevant to the systematic review, we believe that this event still constitutes an update. To undertake an updating process, a systematic search needs to be initiated with the purpose of determining whether or not new evidence exists. 881
Carbohydrates: how low can you go? See Case Report page 958
In today’s Lancet, Tsuh-Yin Chen and colleagues1 describe a patient admitted to hospital for ketoacidosis presumably as a result of following the Atkins lowcarbohydrate diet. The Atkins diet can be appealing to overweight and obese individuals because it boasts good health and, most importantly, rapid weight loss without hunger in the first and most restrictive stage of the diet.2 This dangling carrot often provides the motivation needed to propel individuals to continue with a diet that they might otherwise quit within the first few days because of its significant restriction in food choices. While the rapid weight loss seems to be an obvious benefit of the Atkins diet, bigger questions remain: first, is the diet safe? And second, can this early success motivate individuals to maintain dietary changes for a lifetime? Low-carbohydrate diets for weight management are far from healthy, given their association with ketosis, constipation or diarrhoea, halitosis, headache, and general fatigue to name a few side-effects.1,3 These diets also increase the protein load to the kidneys and alter the acid balance of the body, which can result in loss of minerals from bone stores, thus compromising bone integrity.4 To date, no low-carbohydrate intervention trials have been of sufficient duration to investigate long-term effects of such dietary changes, and the effects of low-carbohydrate diets on intermediate endpoints, such as kidney enzymes and markers of bone metabolism, are equivocal. However, two 12-month intervention trials5,6 showed no significant difference in weight loss after 12 months between a low-carbohydrate diet and a traditional low-fat diet, although individuals randomised to the low-carbohydrate diet
lost significantly more weight at 6 months compared with the low-fat dieters. Teaching at-risk individuals how to manage their weight in ways that are healthy and can be maintained for a lifetime is of utmost importance. Traditional and healthy weight-control practices include increasing physical activity and modifying dietary patterns, such as increasing intakes of wholegrain products and fruit and vegetables.7,8 Many longitudinal epidemiological studies have shown significantly lower risk of cardiovascular disease,9 stroke,10 cancer,11 and other conditions associated with consumption of fruits, vegetables, and wholegrains; some of these foods are noticeably absent from the menu of low-carbohydrate diets.2 Overall, studies of weight loss undoubtedly show reduced risk of chronic diseases such as hypertension, diabetes, and risk factors for other metabolic conditions, but are we to assume that weight loss by any means will have similar benefits? Chen and colleagues will probably agree that lowcarbohydrate diets should not be recommended for weight loss.1 The American Dietetic Association’s position on weight control is that “successful weight management to improve overall health for adults requires a lifelong commitment to healthful lifestyle behaviors emphasizing sustainable and enjoyable eating practices and daily physical activity”.12 The table shows recommended servings from each food group for the Atkins diet and the 2005 Dietary Guidelines for Americans.13 Clearly, the Atkins diet is not nutritionally balanced. Special care needs to be taken when formulating the best prescription for weight loss, because people choosing to lose weight range from being marginally to
Food group
Atkins diet Induction (2 weeks to 6 months)
2005 US Dietary Guidelines (based on 2000 kcal diet)
Meat, poultry, fish, legumes, nuts Dairy Vegetables Fruit Grains Oils Drinks
Unlimited meat, poultry, eggs, and fish; no legumes or nuts 3–4 oz cheese; no other dairy foods 2 cups lettuce and 1 cup other vegetables (~20 g carbohydrate) None None Unlimited amount 64 fluid oz water No caffeinated drinks Recommended
5·5 oz 3 cups milk (or equivalent amount yoghurt or cheese) 2·5 cups 2 cups 6 oz (half wholegrain) 6 teaspoons No recommendation
Vitamin and mineral supplements
No recommendation
All cups are US cups.
Table: Daily recommended food intake according to Atkins diet and 2005 US dietary guidelines13
880
www.thelancet.com Vol 367 March 18, 2006
Comment
significantly overweight, and might have a wide range of disease risk factors with varying levels of severity. As researchers and clinicians, our most important criterion should be indisputable safety, and low-carbohydrate diets currently fall short of this benchmark. *Lyn M Steffen, Jennifer A Nettleton University of Minnesota School of Public Health, Division of Epidemiology and Community Health, Minneapolis, MN 55454, USA [email protected]
5 6
7 8
9
10
We declare that we have no conflict of interest. 1 2
3 4
Chen TY, Smith W, Rosenstock JL, Lessnau KD. A life-threatening complication of Atkins Diet. Lancet 2006: 367: 958. Astrup A, Larsen TM, Harper A. Atkins and other low-carbohydrate diets: hoax or an effective tool for weight loss? Lancet 2004; 364: 897–99. Freedman MR, King J, Kennedy E. Popular diets: a scientific review. Obes Res 2001; 9 (suppl 1): 1S–40. Metgas CC, Barth CA. Metabolic consequences of a high dietary–protein intake in adulthood: assessment of the available evidence. J Nutr 2000; 130: 886–89.
11
12
13
Foster GD, Wyatt HR, Hill JO, et al. A randomized trial of a lowcarbohydrate diet for obesity. N Engl J Med 2003; 348: 2082–90. Samaha FF, Iqbal N, Seshadri P, et al. A low-carbohydrate as compared with a low-fat diet in severe obesity. N Engl J Med 2003; 348: 2074–81. USDA. MyPyramid.gov: steps to a healthier you. http://www.mypyramid. gov/ (accessed Jan 12, 2005). Nutrition and Food Security Programme. Food-based dietary guidelines in the WHO European region. 2003: http://www.euro.who.int/ Document/E79832.pdf (accessed Jan 12, 2006). Steffen LM, Jacobs DR, Stevens J, Shahar E, Carithers T, Folsom AR. Associations of whole grain, refined grain, and fruit and vegetable consumption with all-cause mortality, incident coronary heart disease and ischemic stroke: the ARIC Study. Am J Clin Nutr 2003; 78: 383–90. Ness AR, Powles JW. Fruit and vegetables, and cardiovascular disease: a review. Int J Epidemiol 1997; 26: 1–13. Malin AS, Qi D, Shu XO, et al. Intake of fruits, vegetables and selected micronutrients in relation to the risk of breast cancer. Int J Cancer 2003; 105: 413–18. Cummings S, Parham ES, Strain GW. Position paper of the American Dietetic Association: weight management. J Am Diet Assoc 2002; 102: 1145–55. US Department of Health and Human Services, US Department of Agriculture. 2005 U.S. Dietary Guidelines for Americans. http:// www.health.gov/dietaryguidelines/dga2005/document/pdf/ dga2005.pdf (accessed Jan 11, 2006).
Systematic reviews: when is an update an update? Governments are investing heavily in the use of systematic reviews to inform health-care policy.1 The value of systematic reviews is best when they are kept up to date, since evidence is continually evolving as new research becomes available. For example, certain healthcare interventions currently known to be effective will be shown to be ineffective or harmful in the future, or vice versa.2 To ignore the emergence of new information might therefore undermine the validity of systematic reviews. Although many researchers have addressed several methodological issues of updating systematic reviews,2–6 none has provided a formal definition of what constitutes an update. The definition7 of “to update” means “to extend up to the present time” or “to include the latest information”. Without a formal definition, investigators and readers could have difficulties in determining whether or not any given systematic review has been updated. Furthermore, researchers who undertake surveys of updating practices or studies that deal with different methods of updating could perceive updating processes differently, leading to inconsistent assessments of how current any given systematic review is. These differences, in turn, will render current and future studies non-comparable. www.thelancet.com Vol 367 March 18, 2006
We believe that the introduction of a formal definition and explanation for this important construct is long overdue. We define an update of a systematic review as a discrete event with the aim to search for and identify new evidence to incorporate into a previously completed systematic review. The central and necessary element of an update is the effort to identify new evidence. We use “new evidence” broadly—evidence that has not been included in the previously completed review. For example, use of the search strategy (eg, MeSH terms, years searched) from the original review, but with an additional database (MEDLINE vs MEDLINE and EMBASE) to identify new evidence, is regarded as an update. Alternatively, updating could be initiated after a specific period of time has elapsed since the completion of the original systematic review, which allows for the identification of new evidence that has emerged during this time. Even if a search does not identify any new evidence relevant to the systematic review, we believe that this event still constitutes an update. To undertake an updating process, a systematic search needs to be initiated with the purpose of determining whether or not new evidence exists. 881