Thermodynamics and weight loss

Message

Thermodynamic principles suggest that diets based on high protein content are less efficiently converted to energy than those based on high calorie content. High protein diets should be more inducive to weight loss.

Reference

RD Feinstein, EJ Fine. "A calorie is a calorie" violates the second law of thermodynamics. Nutritional journal 2004 3: 9 (http://www.nutritionaljournal.com/content/3/1/9)

Background

There is argument about the ability of high protein diets to be associated with weight loss because they are high in protein. Isocaloric diets that are high in carbohydrate or high in protein are argued to convey the same amount of weight loss

In this article the authors examine this proposition with reference to a literature review and to the laws of thermodynamics. They calculate the efficiency of diets with the same calorie content but with different components of carbohydrate, fat, and protein, and therefore their effective calorie content. This is done with reference to their thermic effects (thermogenesis), which are low for carbohydrates, moderate for fats, and high for proteins.

Results

The effect of reducing the carbohydrate content of otherwise isocaloric diets is calculated, starting from a diet comprising carbohydrate:fat:protein of 55:30:15 at 1848 calories. The wasted calories due to thermogenesis amounts to 100 calories when the carbohydrate content is reduced to 21%, and at 8% carbohydrate, the starting level of a number of low carbohydrate diets, the loss is 148 calories.

Comment

Recommendations for weight loss call for small reductions in calories. Changing macronutrient composition to increase protein content can do this, given that the total number of calories is not excessive. Weight loss is not independent of the food we eat. Reducing calories, increasing protein content of diets, and increasing exercise is theoretically justified, and may be sensible.