Image source: L. Brian Stauffer
Champaign, Illinois. The 10-week muscle building and diet program that included 50 middle-aged adults found no evidence that eating a protein-rich diet increased strength or muscle mass more than eating a moderate amount of protein during training. The intervention included a standard strength training protocol with sessions three times per week. None of the participants had previous experience lifting weights.
Posted in American Journal of Physiology: Endocrinology and MetabolismThe researchers say the study is one of the most comprehensive investigations of the health effects of diet and resistance training in middle-aged adults. The participants were 40-64 years old.
The team evaluated participants’ strength, lean body mass, blood pressure, glucose tolerance, and many other health measures before and after the program. They randomly divided the participants into moderate and high protein diet groups. To standardize protein intake, researchers fed each person a freshly cooked ground beef slice and a carbohydrate drink after each training session. They also sent the participants home with an isolated protein drink to consume each evening for the ten 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 about 1.6 grams per kilogram per day,” said Colin McKenna, a graduate student in the Department of Nutrition. Registered dietitian at the University of Illinois Urbana-Champaign who led the study with University of Illinois professor of kinesiology and community health Nicholas Bird. The team kept the calories equivalent in the two group meals, with additions of beef tallow and dextrose.
Study participants kept a food diary and McKenna instructed them every two weeks on their eating habits and protein intake.
In an effort led by Yu of Prof. Food Science and Human Nutrition Professor Hannah Holcher, the team also analyzed gut microbiota in stool samples collected at the start of the intervention, after the first week – during which participants adapted to the new diet but did not participate in physical training – And at the end of the ten weeks. Previous studies have found that diet alone or endurance exercise alone can alter the microbial composition of the digestive system.
“The public health messages were that Americans need more protein in their diet, and this extra protein is supposed to help our muscles grow bigger and stronger,” Bird said. “Middle age is a unique thing because as we get older, we lose muscle, and by default, we lose strength. We want to learn how to maximize our strength so that we can protect better as we get older and ultimately we can.” We remain active in family and community life. “
The US Food and Nutrition Council recommends that adults get 0.8 grams of protein per kilogram of body weight each day to avoid protein deficiency. The team attempted to limit protein consumption in the moderate protein group to the recommended daily allowance, but their dietary diaries revealed that these participants were consuming, on average, 1.1 to 1.2 grams of protein per kilogram of body weight per day. Those in the high-protein group ate about 1.6 grams of protein per kilogram per day – twice the recommended amount.
Baird and colleagues hypothesized that getting protein from a high-quality source like beef and consuming protein far more than the RDA would aid muscle growth and strength in middle-aged adults participating in resistance training. But at the end of the 10 weeks, the team did not see any significant differences between the two groups. Their gains in strength, body fat, lean body mass, glucose tolerance, kidney function, bone density, and other “vital signs” of health were nearly the same.
The only negative change the researchers recorded between groups included changes in the group of microbes that live in the gut. After one week of following the diet, those in the high-protein group noticed changes in the abundance of some gut microbes that previous studies had linked to negative health outcomes. Burd and colleagues found that their strength training intervention reversed some of these changes, increasing beneficial microbes and reducing the abundance of potentially harmful ones.
“We found that high protein intake does not increase strength gains or affect body composition,” Baird said. “It did not lead to more fat mass gain than eating a moderate amount of protein. We did not see more fat loss, and body composition was the same between groups. They gained weight, but the weight gain was from increased lean body mass.”
Bird said the result makes him question the drive to increase protein intake beyond 0.8-1.1 grams per kilogram of body weight, at least in middle-aged weightlifters who consume high-quality animal protein on a regular basis.
McKenna said the team’s interdisciplinary approach and in-depth tracking of participants’ dietary habits outside of the lab make the results easy to understand and apply to everyday life.
“We do have recommendations on healthy eating and we have recommendations on how to exercise, but very little research looks at how the two together affect our health,” she said. The study team included exercise physiologists, registered dietitians, and experts in gut microbiology.
“It allowed us to address every aspect of the intervention in the way it should be,” McKenna said. “We respect the complexity of human health as well as the complexity of our research.”
To reach Nicholas Board, send an email [email protected]
To reach Colin McKenna, send an email [email protected]
The paper “High protein intake during resistance training does not stimulate strength, but modifies gut microbiota in middle-aged adults: a randomized control trial” available online and from the US Bureau of News.
This work was supported by Beef Checkoff, who was only involved in the financial support of the project, without participating in the design, data collection and analysis, nor the interpretation and publication of the report.