Consuming too much protein during weight loss could have a negative effect on a crucial bodily function.

Dieters often turn to high-protein foods to fill up faster, but a new study out of the Washington University School of Medicine has shown that in some cases, consuming too much protein during weight loss could have a negative effect on one crucial bodily function.

The findings, which were published in the journal Cell Reports, showed that older women in particular were at risk for seeing a negative effect of excess protein on their body following a drop in weight. In a study of 34 postmenopausal women, aged 50-65—all of whom were obese but not diabetic—researchers found that over-consumption of protein lead to the elimination of a typical benefit of weight loss: a function that lowers the risk of diabetes.

According to Bettina Mittendorfer, PhD, a professor of medicine at the university, the team of researchers found that "women who lost weight eating a high-protein diet didn't experience any improvements in insulin sensitivity." That sensitivity is a common indicator of metabolic health overall, and is typically raised with weight loss. However, the test group that consumed lower levels of protein showed a 25-30 percent improvement in insulin sensitivity over those who consumed more.

"Women who lost weight while eating less protein were significantly more sensitive to insulin at the conclusion of the study," Mittendorfer says. "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."

While Mittendorfer acknowledges that many women eat more protein in order to boost muscle tissue, she notes that those who had 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."

According to the researchers, this data could have huge health implications for older women planning to embark on a weight loss regime. "Changing the protein content has very big effects," Mittendorfer says. "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."

Though it's not totally clear why insulin sensitivity was affected by a higher level of protein consumption, Mittendorfer recommends post-menopausal women think seriously about the amount included in their diet—the difference could be life-altering.