People who are on a diet regimen consume a high-protein diet to stave off hunger and prevent loss of muscle tissue that often comes with weight loss. But a new study claims that a high-protein diet eliminates an important health benefit of weight loss, which is an improvement in insulin sensitivity (critical to reduce the risk of diabetes).
The study was conducted by researchers at Washington University School of Medicine in St. Louis. The study involved 34 obese postmenopausal women.
‘Postmenopausal women who followed a diet containing recommended daily intake of protein experienced improvements in insulin sensitivity.’
"We found that women who lost weight eating a high-protein diet didn't experience any improvements in insulin sensitivity," said principal investigator Bettina Mittendorfer, PhD, 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 is a marker of metabolic health, which improves with weight loss. The researchers found that women who lost weight while consuming less protein experienced a 25 to 30 percent improvement in their sensitivity to insulin.
Thirty-four postmenopausal women who participated in the study were 50 to 65 years of age. The BMI (Body Mass Index) of all the participants were at least 30, which indicates significant obesity, but none had diabetes.
The study period was for 28 weeks. The participants were randomly divided into three groups. Women in the control group were asked to maintain their weight. In another group, women ate a weight-loss diet that included the recommended daily allowance (RDA) of protein - 0.8 grams per kilogram of body weight.
The third group has women who ate a weight loss diet, but they consumed more protein (1.2 grams per kilogram of body weight).
"We provided all of the meals, and all the women ate the same base diet," Mittendorfer explained. "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 on weight loss."
The research focused on protein intake of postmenopausal women because it is believed that a high-protein diet can help preserve lean tissue, while they lose fat.
"When you lose weight, about two-thirds of it tends to be fat tissue, and the other third is lean tissue," Mittendorfer said. "The women who ate more protein did tend to lose a little bit less lean tissue, but the total difference was only about a pound. We question whether there's a significant clinical benefit to such a small difference."
The researchers found that women who ate the daily recommended amount of protein experienced benefits in metabolism, led by a 25 to 30 percent improvement in their insulin sensitivity.
Improvements in insulin sensitivity lowered the risk for diabetes and cardiovascular disease. However, women on the high-protein diet did not experience those 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."
The researchers are not clear as to why insulin sensitivity did not improve in the group that had a high-protein diet. Mittendorfer said that it's not known whether the same results would occur in men or women already diagnosed with type 2 diabetes.
The findings of the study are published in the journal Cell Reports.