Calories Are NOT All the Same

Not all calories are created equal when it comes to weight loss. We have been told for decades that the source of calories doesn’t matter. A calorie is a calorie is a calorie. Eat more calories than you burn up and you will gain weight. That theory is almost certainly too simple.
An unusually rigorous study compared the effects of three different diets on the ability of people to maintain a new lower body weight. Twenty-one individuals who had lost 10 to 15% of their total weight participated in the trial. They were assigned to a very low-fat, a very low-carb or a low glycemic index diet, each of which had the same number of calories. The volunteers followed the diet for four weeks. At the end of each four-week period, blood pressure, blood fats, and energy expenditure were assessed.
The very low-carb diet resulted in greater energy expenditure of about 300 calories a day. In addition, blood lipid levels and other indicators of metabolic syndrome were most improved on this Atkins-like diet. There were, however, increases in the stress hormone cortisol and the inflammatory marker C-reactive protein.
The low-fat diet was the least favorable. Total energy expenditure was lowest and blood fats and other measures linked to metabolic syndrome were higher.
The researchers endorse the low glycemic index diet. Although the effects on lipids and energy expenditure were intermediate between the other dietary approaches, they felt that the benefits were strong without concomitant risks. They also felt that a low glycemic index diet would be more practical to maintain in everyday life.

[JAMA, June 27, 2012]