Too Much Protein Could Wreck the Benefits of Weight Loss


Adding extra protein to your diet to curb your cravings can be helpful, but too much protein intake could affect your metabolism in a less than desirable way.

A study of 34 postmenopausal women with obesity found that eating too much protein eliminates improvement in insulin sensitivity, which can be critical in lowering diabetes risk.

Image Courtesy: Alpha from Melbourne, Australia, Wagyu rump steak and eggs - Jones the Grocer, Chadstone, CC BY-SA 2.0
Image Courtesy: Alpha from Melbourne, Australia, Wagyu rump steak and eggs – Jones the Grocer, Chadstone, CC BY-SA 2.0

The study, conducted by researchers at the Washington University School of Medicine in St. Louis and published in Cell Reports, said women who lost weight while consuming less protein experienced a 25 to 30 percent improvement in their sensitivity to insulin. Bettina Mittendorfer, the study’s principal investigator, said in a news release that sensitivity to insulin can determine whether a person is eventually diagnosed with diabetes.

“We found that women who lost weight eating a high-protein diet didn’t experience any improvements in insulin sensitivity,” said Mittendorfer, a professor of medicine. “However, women who lost weight while eating less protein were significantly more sensitive to insulin at the conclusion of the study. That’s important because in many overweight and obese people, insulin does not effectively control blood-sugar levels, and eventually the result is type 2 diabetes.”

Insulin sensitivity can reflect metabolic health, and it usually improves with weight loss. The 34 women studied were 50 to 65 years old and all had body mass indexes of at least 30, indicating obesity. None were diabetic.

Three groups were formed for the 28-week study. Women in the control group were asked to maintain their weight, while women in another group ate a weight-loss diet that included the recommended daily allowance of protein, 0.8 grams per kilogram of body weight.

Women in the third group ate a diet designed to help lose weight. They consumed more protein at 1.2 grams per kilogram of body weight. Researchers focused on protein because it’s believed that postmenopausal women who consume extra protein are helping to preserve lean tissue and prevent muscle loss.

“We provided all of the meals, and all the women ate the same base diet,” Mittendorfer said. “The only thing we modified was protein content, with very minimal changes in the amount of fat or carbohydrates. We wanted to hone in on the effects of protein in weight loss.”

The women who ate the recommended amount of protein saw benefits in metabolism, including improvement in their insulin sensitivity. Improvements in insulin sensitivity have the potential to lower the risk for diabetes and cardiovascular disease. Women who were on the high-protein diet didn’t see the same improvements.

“Changing the protein content has very big effects,” Mittendorfer said. “It’s not that the metabolic benefits of weight loss were diminished — they were completely abolished in women who consumed high-protein diets, even though they lost the same, substantial amounts of weight as women who ate the diet that was lower in protein.”

Mittendorfer said she plans to continue the research, as it’s not clear why insulin sensitivity didn’t improve for the group on the high-protein diet. She also said it isn’t clear whether the results would be the same for men or in women already diagnosed with type 2 diabetes.