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Dec9-11, 08:55 PM
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Quote Quote by Yanick View Post
A calorie is a calorie, though lots of people in the diet and fitness industry like to argue this fact. In the end though a calorie is a calorie.
I agree. Feinman and Fine's papers were used by some to claim otherwise:

Reduced thermodynamic efficiency will result in increased weight loss. The laws of thermodynamics are silent on the existence of variable thermodynamic efficiency in metabolic processes. Therefore such variability is permitted and can be related to differences in weight lost. The existence of variable efficiency and metabolic advantage is therefore an empiric question rather than a theoretical one, confirmed by many experimental isocaloric studies, pending a properly performed meta-analysis. Mechanisms are as yet unknown, but plausible mechanisms at the metabolic level are proposed.
Thermodynamics of weight loss diets

But here is a summary of the research suggesting that Feinman's and Fine's arguments are not warranted:

We thank Manninen and Feinman and Fine for their interest in our review, "Is a Calorie a Calorie?" . These 2 letters correctly point out that there are indeed some differences between the energetics of human metabolism and the measures of heat release of nutrients in a bomb calorimeter. We agree with the known concept that the metabolic route through which carbon flows to carbon dioxide, the concentrations of substrates, as well as entropy can all slightly alter the efficiency of ATP production in humans. This concept, however, does not automatically mean that these differences constitute a quantitatively plausible mechanism that would explain the differences in weight loss observed with a high-protein, energy-restricted diet relative to a low-fat, energy-restricted diet.

Rather than relying on a theoretical treatment of metabolic efficiencies, as did Feinman and Fine, we reviewed studies in which known experimental diets were fed to subjects under laboratory conditions to test whether energy expenditure was actually higher with a low-carbohydrate diet than with a high-fat diet. In studies in which protein intake was held constant and fat was substituted for carbohydrate, the difference in 24-h energy expenditure between the high-carbohydrate and high-fat diets was not different from zero . However, as clearly stated in our review, when the protein intake was not held constant but rather increased from 15% to 30-35% of energy, 24-h energy expenditure did increase. We determined, however, that the increase would be only 41 kcal/d for a 1500-kcal/d energy-restricted diet. This would only increase weight loss by 0.04 kg/wk, or 0.44 kg over a 12-wk course of weight-loss treatment. It should be noted that this is less than the 95 kcal/d calculated theoretically by Feinman and Fine, and it has the advantage of being based on experimental data. Thus, we do not disagree with Feinman and Fine from the perspective of pure thermodynamics; in fact, we resented evidence at the whole-body level that supports their point. However, we found the experimentally measured differences in 24-h energy expenditure, between subjects who followed a high-protein diet compared with those who followed a high-carbohydrate diet, to be too small to satisfactorily account for the differences in weight loss observed after 12 wk of treatment with these 2 diets. Thus, this is not a plausible mechanism to account for the observed increased weight loss. The experimental data on energy expenditure provide evidence of only a minimal metabolic advantage for low-carbohydrate diets.
In addition, we concede that the substitution of one macronutrient for another has been shown in some studies to have a statistically significant effect on the expenditure half of the energy balance equation. This has been observed most often for high-protein diets. Evidence indicates, however, that the difference in energy expenditure is small and can potentially account for less than one-third of the differences in weight loss that have been reported between high-protein or low-carbohydrate diets and high-carbohydrate or low-fat diets. As such, a calorie is a calorie.
Is a calorie a calorie?