Are all calories equivalent for fat loss?

The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective. During isocaloric feeding following weight loss, REE was 67 kcal/d higher with the very low-carbohydrate diet compared with the low-fat diet. TEE differed by approximately 300 kcal/d between these 2 diets, an effect corresponding with the amount of energy typically expended in 1 hour of moderate-intensity physical activity.

In comparative studies, obese patients given a low-carbohydrate (4.14 MJ [1000 kcal]) formula diet (diet Ia) lost 14.0 +/- 1.4 kg and those given an iso-energetic high-carbohydrate diet (diet Ib) 9.8 +/- 0.9 kg. The degree of weight loss was significantly different. Daily weight losses were 362 g and 298 g respectively…there was a greater mean weight loss with the low-carbohydrate diet (351 g/day) compared with that under the high-carbohydrate diet (296 g/day).

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.

The time-restricted mice on a high-fat diet were protected from the adverse effects of a high-fat diet and showed improvements in their metabolic and physiological rhythms. They gained less weight and suffered less liver damage. The mice also had lower levels of inflammation, among other benefits.

When it comes to weight gain, when you eat might be at least as important as what you eat. That's the conclusion of a study reported in the Cell Press journal Cell Metabolism published early online on May 17th.

Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize.

Rabast and company did not measure body composition among their subjects. So we don’t know whether the lost weight came from water, lean tissue, or fat. But some of their other data indicates that the extra losses came from lean tissue, glycogen and/or water. In their 1981 study, Rabast et al observed significantly greater potassium excretion on the low-carbohydrate diets during weeks one and two. A considerable amount of the potassium inside our bodies is bound up with glycogen, so the greater potassium losses in Rabast's low-carbohydrate dieters may indeed be a reflection of greater glycogen, and hence water losses.

Because considerable potassium is bound up with hydrated glycogen (0.45 mmol K/g glycogen), the loss will result of > 200 mmol K.

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.

Increased meal frequency does not appear to significantly enhance diet induced thermogenesis, total energy expenditure or resting metabolic rate.

We conclude that increasing meal frequency does not promote greater body weight loss under the conditions described in the present study.

These findings upend the long-held assumption that our hunter-gatherer ancestors expended more energy than modern populations, and challenge the view that obesity in Western populations results from decreased energy expenditure. Instead, the similarity in daily energy expenditure across a broad range of lifestyles suggests that habitual metabolic rates are relatively constant among human populations. This in turn supports the view that the current rise in obesity is due to increased food consumption, not decreased energy expenditure.

In conclusion, appetite suppression and fat oxidation were higher on a high-protein diet without than with carbohydrates exchanged for fat. Energy expenditure was not affected by the carbohydrate content of a high-protein diet.

The bottom line is that there is no metabolic advantage to a low carbohydrate intake that is independent of a high protein intake. There is a metabolic advantage to a high protein diet, which will increase the calories you burn by 80-100 calories per day. There is also a dramatic satiety advantage to a high protein intake. A low carbohydrate intake (low enough to cause ketosis) can increase this satiety advantage, but individual responses will vary. The best dietary approach for you will depend upon a variety of factors.