Dietary protein affects lean weight gain, but not fat gain, during overeating

A January 2012 JAMA study reports that people eating 40% more calories than they expended for eight weeks gained the same amount of body fat regardless whether they ate protein at 5% (low protein), 15% (normal protein), or 25% (high protein) of calories.

But the amount of lean (muscle) weight gain (and thus total weight gain) and resting energy expenditure were influenced by the amount of protein eaten.

The weight gain in the low protein diet group was 3.16 kg, about half that of the other 2 groups (normal protein diet: 6.05 kg; high protein diet: 6.51 kg; P = .002). The rate of weight gain in the low protein diet group was significantly less than in the other 2 groups (P < .001). The failure to increase lean body mass in the low protein group accounted for their smaller weight gain [emphasis added]. …

Resting energy expenditure, total energy expenditure, and body protein did not increase during overfeeding with the low protein diet. In contrast, resting energy expenditure … and body protein (lean body mass) … increased significantly with the normal and high protein diets. Continue reading