Can extra protein help you lose—or not gain—weight?

No doubt, getting enough protein matters. Eat too little and you’ll lose muscle.

Conquering cravings and satisfying hunger are ad-speak for a bigger prize: getting or staying trim.

“To many people, protein is good because protein is lean,” says Bettina Mittendorfer, professor of medicine and nutritional science at the Washington University School of Medicine in St. Louis.

But does extra protein help you eat less?

Even when studies—often funded by the dairy, beef, pork, or egg industry—find that extra protein makes people feel more full, it has little or no impact on their weight.

For example, when researchers gave 151 dieters an extra 45 grams a day of whey protein or soy protein for six months, the dieters felt slightly more full after consuming the whey supplements, but they kept off no more weight than those who got a control powder (maltodextrin) with the same calories.

Why protein isn't weight-loss magic

In Pounds Lost, the largest, longest clinical trial to look, dieters who were randomly assigned to eat higher-protein diets lost no more weight after two years than those assigned to eat normal-protein diets.

“Over the long term, there’s really no good evidence that protein makes you leaner or makes you eat less,” says Mittendorfer.

And there’s no reason to believe that if you overeat protein, it’s more likely to end up as muscle, not fat.

In a carefully controlled study, researchers fed 25 healthy young people diets that got 5 (low), 15 (normal), or 25 (high) percent of calories from protein. All three diets had 40 percent more calories than the participants needed (about 1,000 extra calories a day).

After two months, all three groups had gained the same amount of body fat. The only difference: the low-protein group gained less weight  (7 pounds) than the normal-protein (13 pounds) and high-protein (14 pounds) groups.

Why? “Those who didn’t get enough protein lost some muscle,” explains Mittendorfer.

So if you justify that oversized steak as harmless muscle fuel, you’re fooling yourself. “As you gain weight, you mostly put on fat, not muscle,” says Mittendorfer.

Photo: Mara Zemgaliete/