There’s a rumor going around the gym, and it goes something like this: Eat too much protein, and it’ll just get converted to fat.
As people who eat roughly our body weight in chicken breast every week, we decided to put this rumor to rest.
“Protein is insulinogenic, meaning it can stimulate an insulin response, which puts the body in storage mode,” explains Jackie Buell, Ph.D., C.S.S.D., an assistant professor and sports dietitian at Ohio State University.
So to be clear: Yes, your body can transform the calories from excess protein into fat. However, no study has conclusively shown how much protein you can eat before your body starts changing that protein to fat. In fact, we do know that the protein-to-fat-transformation threshold is fairly high, because a number of studies have researched what happens when people eat lots of protein, and none of those studies reported changes in body fat composition.
A 2016 study in the Journal of Nutrition and Metabolism found that when healthy guys consumed 3.3g of protein per kilogram of body weight per day (g/kg/d) for four months, they didn't gain any fat compared to when they ate a traditionally healthy diet. (Nor did they have any changes to their blood lipids or liver and kidney function, by the way).
Another widely cited study in the Journal of the International Society of Sports Nutrition found that when healthy, resistance-trained guys upped their protein to 4.4g/kg/d—that's five and a half times the recommended daily allowance—their body fat didn't go up whatsoever over two months. (Competing interest alert: One of the study authors is the CEO of the ISSN, which is sponsored by two supplement companies that supplied protein supplements for the study. Make of that what you will.)
What’s more, a small 2016 study published in the Journal of the International Society of Sports Nutrition found that when healthy guys ingested up to 3.3g/kg/d of protein and continued their normal strength regimen, they actually lost fat over the four-month period.
“Bottom line: Protein in doses higher than the recommended daily allowance of 0.8g/kg/d appear to benefit most people, barring those with pre-existing health or kidney medical problems,” says Michael Ormsbee, Ph.D., C.S.C.S., associate director of the Institute of Sports Sciences & Medicine at Florida State University.
So the question then becomes: If the excess doesn’t build fat, then where is it going? We need more research to fully answer that, Ormsbee says. Buell points out that your body has multiple uses for protein: Your liver decides the fate of amino acids first, and it can ship them out to other tissues to use for muscle repair or for energy, it can keep the amino acids and use them to make more proteins, or it can use them for energy to make glucose or fat, depending on the structure of the particular amino acid.
“We do know that excess intake can also increase the amount we excrete”—meaning protein that just gets flushed out of your system—“so that has to be taken into consideration too,” Ormsbee adds.
And if you’ve increased your protein and feel like you’ve gained fat, your protein intake probably isn’t at fault.
If you subscribe to a “traditional Western” diet and you’re scoring most of your protein through relatively high-fat sources—like meats, cheese, or full-fat yogurt—then yes, you’ll likely gain weight. But it’s not the protein that’s the problem, or the fat, for that matter (just look at every ripped guy on the Keto diet)—it’s the overall calorie count. “Over-consuming calories will lead to weight gain, no matter what nutrient,” Buell says.
And yes, protein powders have calories, Ormsbee adds. Every gram of protein, regardless of its source, has about 4 calories, Buell explains. If your powder has 20g of protein, then that’s at least 80 calories, not including the fat and carbs added to many powders to improve taste and texture.
So how do you increase your protein intake without also risking an increase in your body fat? Focus on a meal’s protein count first, and fill the rest of the plate with healthy carbs, fats, and vegetables, Ormsbee suggests.
And time it right, too. By combining regular exercise with “protein pacing”—that is, pacing a daily protein intake of 2g/kg over five to six meals a day, about every three hours—men and women of all physical builds can improve their body composition without gaining fat, according to extensive research conducted by Paul Arciero, D.P.E., at Skidmore College.