Eating too much is what makes us gain weight, and calories alone are more significant than protein when it comes to a weight-loss regime. 

That’s the finding of a new study published in the current issue of JAMA, the Journal of the American Medical Association.

The study involved 25 healthy men and women, 18 to 35 years old, who ate prescribed diets under supervision at the Pennington Biomedical Research Center. The recruits were fed either a low-protein diet in which 5 percent of their caloric intake came from proteins, a typical protein diet (15 percent from proteins), or a high protein diet (25 percent from proteins) for about 12 weeks. For the last eight weeks they were fed an 1,000 calories a day more than the normal American diet (40 percent more than needed) to determine whether the amount of protein made a difference when it came to weight gain from excess calories.


The people on the low-protein diet gained fewer pounds: about 6 pounds over eight weeks compared to about 13 pounds for those on a diet with typical protein intake and 14 pounds for the high-protein regime.

No matter how much or how little protein they ate, the participants all gained weight and the same amount of body fat.

Dr. George Bray, lead author of the study, explained: “The hypothesis was that the low-protein and high-protein diets might affect fat gain, but they didn’t … fat gain isn’t modulated to any significant degree by protein intake.”

In other words, overall calorie intake, not the amount of protein in one’s diet, is what influences weight loss.

The researchers said there was no evidence that eating more than 12 to 15 percent of calories in protein slowed weight gain or improved body composition.

And while those whose diets were low in protein gained less weight overall than people on high- and moderate-protein diets, that’s because the low-protein group also lost muscle mass, not fat.

Dr. Jules Hirsch, head of the Laboratory of Human Behavior and Metabolism at Rockefeller University, New York, said the study shows that “no caloric mixture, everything we’ve tried, nothing has been demonstrated to be causative other than excess total consumption,” both in causing obesity and in designing effective interventions.

“What the paper shows is that varying the particular dietary contents is not what counts, but getting caloric count down is where we need to be,” Dr. Hirsch told Medscape Medical News.

So what’s the sensible amount of protein in a diet?

The USDA’s recommends about 5-6 ounces of protein foods a day for most adults.

In general, 1 ounce of meat, poultry or fish, ¼ cup cooked beans, 1 egg, 1 tablespoon of peanut butter, or ½ ounce of nuts or seeds can be considered as a 1 ounce equivalent from the Protein Foods Group, according to the recommendations.

The Centers for Disease Control and Prevention says people eat more protein than they need without harmful effects, but note that protein contributes to calorie intake, so if you eat more protein than you need, your overall calorie intake could be greater than your calorie needs and contribute to weight gain.

The CDC lists the Recommended Dietary Allowances for protein by grams by different age groups, and explains that 1 cup of milk has 8 grams of protein, a 3-ounce piece of meat has about 21 grams of protein, a 1 cup of dry beans has about 16 grams of protein and an 8-ounce container of yogurt has about 11 grams of protein. Added together, just these four sources would meet the protein needs of an adult male (56 grams).