When it comes to gaining body fat, how many calories you eat seems to count more than whether those calories come from plenty of protein or little protein.
Researchers found that people who ate high-calorie diets all gained about the same amount of body fat. Those whose diets were low in protein gained less weight overall than people on high- and moderate-protein diets. However, the researchers found that was because the low-protein group also lost muscle.
Bottom line: when it comes to fat gain, it is calories that count.
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.
For the current study, researchers 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 determined exactly how many calories each participant needed to maintain their body weight.
Then, for eight weeks, they added roughly 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 5 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.
Experts say it's difficult to see how the findings apply to a general population that isn't being overfed such a protein-deficient diet, in the case of the low-protein group.
However, there are a couple of messages that people can take away from the findings - namely weight gain or loss might not be the best way to track how healthy a person's diet is.
In other words, the scale 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 muscle which isn't healthy.
But at the end of the day, if you overeat calories, no matter where they come from, you'll gain more body fat.
SOURCE: Journal of the American Medical Association, online January 3, 2012.
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