More protein doesn't mean more strength in resistance-trained middle-aged adults
A 10-week muscle-building and dietary program involving 50 middle-aged adults 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 intervention involved a standard strength-training protocol with sessions three times per week. None of the participants had previous weightlifting experience.
Published in the American Journal of Physiology: Endocrinology and Metabolism, the study is one of the most comprehensive investigations of the health effects of diet and resistance training in middle-aged adults, the researchers say. 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 randomized 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. They also sent participants home with an isolated-protein drink to be consumed every evening throughout the 10 weeks of the study.
“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,” said Colleen McKenna, a graduate student in the division of nutritional sciences and registered dietician at the University of Illinois Urbana-Champaign who led the study with U. of I. kinesiology and community health professor Nicholas Burd. The team kept calories equivalent in the meals provided to the two groups with additions of beef tallow and dextrose.
The study subjects kept food diaries and McKenna counseled them every other week about their eating habits and protein intake.
In an effort led by U. of I. food science and human nutrition professor Hannah Holscher, the team also analyzed gut microbes in fecal samples collected at the beginning of the intervention, after the first week — during which participants adjusted to the new diet but did not engage in physical training — and at the end of the 10 weeks. Previous studies have found that diet alone or endurance exercise alone can alter the composition of microbes in the digestive tract.


