To the Editor: Sacks et al. (Feb. 26 issue)1 compare weight-lossdiets that vary in macronutrient content, with a targeted maximaldifference in the proportion of calories derived from carbohydrates,fat, and protein of 30, 20, and 10 percentage points, respectively.The realized macronutrient differences were substantially smallerthan the planned targets, and at 2 years, weight loss was similarin pairwise comparisons of intakes at the high and low extremesof each macronutrient. Neither the targeted nor the actual intakesof carbohydrates or fat in any of the diets would classify themas being substantially low in these macronutrients. Unfortunately,the diets were portrayed this way in the media.2 Given the smalldifferences in reported macronutrient intake and the even smallerdifferences in biomarker-predicted intakes, one may concludethat small differences in dietary macronutrient content do notaffect weight loss. However, the question of whether largerdifferences in macronutrients preferentially promote weightloss remains unanswered by this study.
Christy L. Boling, M.D. Durham Veterans Affairs Medical Center Durham, NC 27705 christy.boling{at}duke.edu
Eric C. Westman, M.D., M.H.S. Duke University Medical Center Durham, NC 27710
William S. Yancy, M.D., M.H.S. Durham Veterans Affairs Medical Center Durham, NC 27705
References
Sacks FM, Bray GA, Carey VJ, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med 2009;360:859-873. [Free Full Text]
Parker-Pope T. Study zeroes in on calories, not diet, for loss. New York Times. February 25, 2009.
The authors reply: Boling and colleagues raise a valid point.We did not test very-low-carbohydrate intake because we hada concern — based on previous studies — that participantswould not be able to sustain such a low intake beyond the initial2 to 4 months, even with continual instruction and assistancefrom the research staff of dietitians and behavioral psychologists.For example, Foster et al. found that after 3 months there wasno difference in levels of urinary ketones between participantswho were assigned to the Atkins diet, which starts with an intakeof 20 g or less of carbohydrates per day and increases to anintake of 50 g or less per day (approximately 10% of the dailyrequirement of kilocalories), and participants who were assignedto conventional diets.1 Foster and colleagues opined that long-termadherence may be difficult, and other studies support this view,showing that adherence to carbohydrate goals deteriorates within2 to 3 months and that intake increases to 37% at 6 months2and to approximately 34 to 40% at 12 months.3,4,5 The Atkinsapproach may work well for some persons, but the data from randomizedtrials provide support for the view that low-carbohydrate diets,whether extreme or moderate, do not consistently result in moreweight loss than other approaches. Moreover, our findings confirmthat despite best efforts, studies that compare diets for weightloss have not shown large differences in dietary macronutrientcomposition.
Frank M. Sacks, M.D. Harvard School of Public Health Boston, MA 02115 fsacks{at}hsph.harvard.edu
George A. Bray, M.D. Pennington Biomedical Research Center Baton Rouge, LA 70808
Catherine Loria, Ph.D. National Heart, Lung, and Blood Institute Bethesda, MD 20892
References
Foster GD, Wyatt HR, Hill JO, et al. A randomized trial of a low-carbohydrate diet for obesity. N Engl J Med 2003;348:2082-2090. [Free Full Text]
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;348:2074-2081. [Free Full Text]
Dansinger ML, Gleason JA, Griffith JL, Selker JP, Schaefer EJ. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA 2005;293:43-53. [Free Full Text]
Gardner CD, Kiazand A, Alhassan S, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women. JAMA 2007;297:969-977. [Erratum, JAMA 2007;298:178.] [Free Full Text]
Shai I, Schwarzfuchs D, Henkin Y, et al. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. N Engl J Med 2008;359:229-241. [Free Full Text]
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