Is A Calorie A Calorie, Or Not?

It is well known that weight loss is difficult to maintain. Some of this difficulty is attributed to decrease in energy expenditure as the body loses weight. A recent study indicated that after losing weight people who ate a high protein, high fat, low carbohydrate diet (low glycemic load, low glycemic index) burned more calories (energy expenditure) than those who ate a high carbohydrate, low protein, low fat diet (high glycemic load, high glycemic index). The two diets contained the same amount of calories. A third diet with the same amount of calories but with balance between the carbohydrates, protein and fat was in the middle for energy expenditure but somewhat closer to the high protein, high fat, low carbohydrate diet. The carbohydrates in the third diet consisted of less starchy vegetables and grains (moderate glycemic load, low glycemic index). The difference in energy expenditure between the high protein, high fat, low carbohydrate and the highest carbohydrate, low protein, low fat diets was statistically significant and the authors indicated this difference represented the equivalent of one hour of moderately intensive physical activity.

To their credit the authors did not extrapolate wildly from the findings. They mentioned that a calorie may not have the same metabolic effect between different diets in the situation they studied. The study did not address micro-nutrients. A disturbing observation was the increased cortisol excretion, elevated C-reactive protein (inflammation) and decreased insulin sensitivity with the high protein, high fat, low carbohydrate diet.

A critique of the study by Dr. Jules Hirsch was published in the NY Times. He begged to differ with the authors about a calorie not being a calorie and suggested other reasons for the findings; the principle one being loss of water with a high fat, high protein, low carbohydrate diet. Also, he observed that without decreasing the fat content there is no decrease in obesity.


It is easy to miss the goal of decreasing obesity and improving health when submerged among all the details. Nutrition, metabolism and lifestyles are complex and the public often gets confused. Hey, everyone gets confused from time to time and experts do not always agree.