Obesity: It's ALL About Calories

When it comes to packing on body fat, how many calories you eat seems to count more than where those calories come from -- lots of protein, or very little.

Researchers found that people who ate high-calorie diets all gained about the same amount of fat. Those whose diets were low in protein gained less weight overall than people on high- and moderate-protein diets, but that's because the low-protein group also lost muscle.

Previous research has suggested that when people over-eat, the amount of weight they gain varies from person to person. Whether the make-up of individuals' diets might be affecting how their body stores the extra calories has remained unclear, though.

Researchers led by Dr. George Bray from the Pennington Biomedical Research Center in Baton Rouge, Louisiana, recruited 25 young, healthy volunteers to live in their lab and eat a prescribed diet for two to three months.

During the first couple of weeks, the researchers tinkered with participants' diets to determine exactly how many calories they needed to maintain their body weight. Then, for eight weeks, they piled on about 1,000 extra calories to those daily diets. One-third of the participants were fed a standard diet with 15 percent of their calories coming from protein, while the others ate low- or high-protein diets with either five or 25 percent of calories from protein. That worked out to volunteers eating an average of 47, 139 or 228 grams of protein per day.

Those diets made everyone gain weight, but not equally. The low-protein diet group put on about seven pounds per person, compared to 13 or 14 pounds in the normal- and high-protein groups.

But people in the low-protein group stored more than 90 percent of their extra calories as fat and lost body protein (muscle mass), while other participants gained both fat and healthier lean muscle. So the groups all gained a similar amount of total excess fat.

Dr. James Levine, who studies obesity at the Mayo Clinic in Rochester, Minnesota and was not involved in the study, stated that, "Huge swings in protein intake do not result in huge swings in body fat gain." "It really is the calories that count." "There are a couple of messages that people outside of a strict scientific study can take away from the findings -- especially that weight gain or loss might not be the best way to track how healthy a person's diet is."

Bray agreed, and stated that, "The scale that you step on isn't necessarily a good guide to the kind of weight you're gaining."

"People who had the low protein gained about half as much weight as those that had normal or high protein, but the weight was different in one major component: they lost body protein, which is not healthy," Bray said. "The scale can fool you into thinking that you're winning when you aren't."

Regardless of that number, he concluded, "If you over-eat extra calories, no matter what the composition of the diet is, you'll put down more fat."

Journal of the American Medical Association, online January 3, 2012