While many believe that a high-protein diet can help with weight loss, a new study finds it might actually prevent an important health benefit that comes with slimming down.
The research found that when you lose weight on a high-protein diet, there's no improvement in what doctors call "insulin sensitivity" – a factor that could lower your risk for diabetes and heart disease.
In type 2 diabetes, cells gradually lose insulin sensitivity – their ability to respond to the metabolic hormone.
This often occurs with rising obesity, so improved insulin sensitivity can be one of the byproducts of weight loss.
However, "we found that women who lost weight eating a high-protein diet didn't experience any improvements in insulin sensitivity," said study principal investigator Bettina Mittendorfer. She's a professor of medicine at Washington University School of Medicine in St. Louis.
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.
Type 2 diabetes
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.
One expert nutritionist said the findings make sense, metabolically speaking.
"Your body needs protein. But consuming an amount of protein beyond your needs is unnecessary, may be harmful if you have kidney issues, and can lead to weight gain since excess calories from protein are stored as fat," explained Stephanie Schiff. She's a registered dietitian at Huntington Hospital in Huntington, New York.
"For obese, postmenopausal women, add in the factor of decreased insulin sensitivity and the perceived benefits from high-protein diets are lost," she said.
Schiff believes the healthiest diet is a "balanced" one that includes complex carbohydrates as well as a recommended level of daily protein.
However, one diabetes expert believes healthy weight loss is typically beneficial in terms of preventing diabetes – even if it involves high-protein regimens.
"Most of the time people who lose weight become more insulin sensitive," said Dr Gerald Bernstein, who coordinates the Friedman Diabetes Programme at Lenox Hill Hospital in New York City.
He believes exercise is key, too.
"A reasonable amount of physical activity can increase insulin sensitivity in muscles," Bernstein said, "and we generally work on caloric restriction and physical activity together."
The findings were published in the journal Cell Reports.