It might be time to shift the goal for obesity treatment away from just weight loss and body mass index to include fat reduction and a better understanding of nutrition science, say the authors of a Journal of the American Medical Association study (2012; 307 [1], 47–55).

At the crux of their findings? Body fat increased when healthy subjects took in more calories than they burned, and the calories themselves appeared to be more important than the amount of protein ingested. When subjects consumed more calories than they expended each day, they appeared to gain body fat and lose lean muscle if their food choices were low in protein.

“Among persons living in a controlled setting, calories alone account for the increase in fat; protein affected energy expenditure and storage of lean body mass, but not body fat storage,” concluded the authors.

The study. Twenty-five healthy people, aged 18–35, spent time in a controlled setting and were randomized to overconsume diets containing various amounts of protein.

Here were the key findings:

  • Overeating produced significantly less weight gain in the low-protein diet group compared with the normal-protein diet group or the high-protein diet group.
  • Body fat increased similarly in all three protein diet groups and represented 50% to more than 90% of the excess stored calories.
  • Resting energy expenditure, total energy expenditure and body protein (lean body mass) did not increase during overfeeding with the low-protein diet. In contrast, resting energy expenditure and lean body mass increased significantly with the normal- and high-protein diets.