In a new study, researchers conducted a 10-week muscle-building and dietary program involving 50 middle-aged adults.
The intervention involved a standard strength-training protocol with sessions three times per week.
The researchers found no evidence that eating a high-protein diet increased strength or muscle mass more than consuming a moderate amount of protein while training.
The research was done by a team at the University of Illinois Urbana-Champaign.
In the study, the team examined the health effects of diet and resistance training in middle-aged adults. Participants were 40-64 years of age.
The team assessed participants’ strength, lean body mass, blood pressure, glucose tolerance and several other health measures before and after the program.
They assigned participants into moderate- and high-protein diet groups. To standardize protein intake, the researchers fed each person a freshly cooked, minced beef steak and carbohydrate beverage after every training session.
The moderate-protein group consumed about 1.2 grams of protein per kilogram of body weight per day, and the high-protein group consumed roughly 1.6 grams per kilogram per day.
At the end of the 10 weeks, the team saw no differences between the groups.
Their gains in strength, body fat, lean body mass, glucose tolerance, kidney function, bone density, and other “biomarkers” of health were roughly the same.
The only potentially negative change researchers recorded between the groups involved alterations to the population of microbes that inhabit the gut.
After one week on the diet, those in the high-protein group saw changes in the abundance of some gut microbes linked to negative health outcomes.
Their strength-training intervention reversed some of these changes, increasing beneficial microbes and reducing the abundance of potentially harmful ones.
The findings showed that high protein intake does not further increase gains in strength or affect body composition.
It didn’t increase lean mass more than eating a moderate amount of protein.
The finding makes researchers question the push to increase protein intake beyond 0.8-1.1 grams per kilogram of body weight, at least in middle-aged weightlifters consuming high-quality animal-based protein on a regular basis.
The study is published in the American Journal of Physiology: Endocrinology and Metabolism. One author of the study is Colleen McKenna.
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