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Editor's Correspondence
May 9, 2005

All Calories Are Not Equal

Arch Intern Med. 2005;165(9):1069. doi:10.1001/archinte.165.9.1069-a

In response to the letter by Seshadri,1 we agree that emphasis on intake of complex carbohydrates over simple carbohydrates may be preferred in fat-reduced diets owing to their greater effects on satiety2; however, we believe that certain points regarding our article3 and study have been misinterpreted. We examined the effects of an ad libitum high–complex carbohydrate diet on body weight and body composition. The subjects in this study were provided 150% of estimated energy needs, not estimated prestudy energy intake; that is, our goal was to provide a surfeit of food that would not be consumed in its entirety. In this way, we were able to measure actual food intake by weighing all food provided to each subject before and after each day. Assessment of free-living energy intake is difficult due to frequent underreporting,4 and as described in our results, the apparent 1000 kcal/d increase in intake during the intervention compared with baseline in the control subjects was likely due to methodologic differences between the 2 measurement periods (ie, food records vs measured weight of consumed food). The important conclusion of this study was that weight loss was experienced by subjects consuming an ad libitum high-carbohydrate diet with no attempt at energy restriction. Our results also indicated that subjects lost weight with no significant reduction in energy intake. The human body is not a bomb calorimeter, and the notion that all macronutrients are metabolized in an equivalent fashion is untenable. For example, classic studies by Sims and Danforth5 demonstrated that weight gain is accomplished with almost 5-fold fewer kilocalories on a high fat vs mixed diet. The metabolic fate of ingested carbohydrate is glycogen storage and oxidation6 with a trivial amount directed toward de novo lipogenesis, while the storage of dietary fat as fat is remarkably efficient. The data from this study strongly supports the hypothesis7 that fat balance is maintained by fat oxidation and fat consumption. The reduction of fat intake with no change in the rate of fat oxidation can result in the loss of body fat even when total energy intake is unchanged.

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