Mittendorfer’s team tracked outcomes over seven months for 34 obese women aged 50 to 65, none of whom had diabetes at the study’s outset. The women were divided into three groups: a no-dieting group where women simply maintained their weight; a dieting group that ate the recommended daily level of protein; and a dieting group that stuck to a high-protein regimen.
At the end of the study period, women who ate a high-protein diet did not show improvement in insulin sensitivity, an important factor in reducing diabetes and heart disease risk.
The women who dieted but ate the standard amount of protein had a 25 to 30 percent improvement in their insulin sensitivity, the researchers reported.
“Women who lost weight while eating less protein were significantly more sensitive to insulin at the conclusion of the study,” Mittendorfer said in a university news release. “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,” she explained.
The researchers also found that consuming high levels of protein offered little benefit in terms of preserving muscle while dieting.
“When you lose weight, about two-thirds of it tends to be fat tissue, and the other third is lean tissue,” Mittendorfer noted. “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.”
It’s not known why insulin sensitivity didn’t improve among women who ate high-protein diets, or if the same results would occur in men or in women already diagnosed with type 2 diabetes, the study authors said.