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September 19, 2012

Dietary Composition During Weight-Loss Maintenance

Author Affiliations

Letters Section Editor: Jody W. Zylke, MD, Senior Editor.

Author Affiliation: Division of General Medicine and Epidemiology, University of North Carolina School of Medicine, Chapel Hill (maweaver@email.unc.edu).

JAMA. 2012;308(11):1087. doi:10.1001/2012.jama.11611

To the Editor: Dr Ebbeling and colleagues1 conducted a crossover trial to examine energy expenditure during weight-loss maintenance with a low-fat, a low–glycemic index, and a very low-carbohydrate diet. They found decreases in energy expenditure that were greatest with the low-fat diet and least with the very low-carbohydrate diet.

I believe the authors overinterpreted 1 key result in their study. They commented that “C-reactive protein [CRP] also tended to be higher with the very low-carbohydrate diet” and concluded that the very low-carbohydrate diet “may increase cortisol excretion and CRP.” The authors implied that the low–glycemic index diet may be preferable to the very low-carbohydrate diet despite the fact that the latter outperformed the former on most key outcome measures. However, the overall null hypothesis of equal mean CRP values across the 3 diets could not be rejected at the specified .05 significance level, with a P value of .13. Nevertheless, the authors reported the results of a test for linear trend across the 3 diets, arranged from highest to lowest glycemic load and assuming equal spacing, with a corresponding P value of .05. It is this test that the authors used to support the conclusion.

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