It is widely known that dietary protein provides essential nutrients that control a range of processes in the body, and it can influence both our health and lifespan. Its consumption is in general thought of as being good for us and helps to promote muscle growth and strength, especially when combined with exercise. However, too much protein can increase the risk of heart disease, diabetes, and death in those with a sedentary lifestyle.
“We know that low-protein diets and diets with reduced levels of specific amino acids promote healthspan and lifespan in animals, and that the short-term restriction of protein improves the health of metabolically unhealthy, adult humans,” explains lead author Michaela Trautman, Research Assistant at the Department of Medicine, School of Medicine and Public Health, University of Wisconsin, US. “But this presents a paradox — if high dietary protein is so harmful, many people with high-protein diets or protein supplements would be overweight and at an increased risk of diabetes, whereas athletes with high-protein diets are among the most metabolically healthy.”
To examine the possible protective effects of exercise against the detrimental effects of a high-protein diet, the researchers used a progressive resistance-based strength training program in mice. Three times a week for a three-month period the animals pulled a cart down a track carrying an increasing load of weight, while controls pulled an identical cart with no weight. One group of mice was fed a low-protein diet consisting of 7% of calories from protein, and another group was fed a high-protein diet consisting of 36% of their calories from protein. The researchers compared body composition, weight, and metabolic measures such as blood glucose between the groups of mice.
According to the researchers, mice on the high protein diet in the no-weight-pulling group had impaired metabolic health, and these mice gained excess fat compared to their counterparts on a low protein diet. Mice on a high-protein diet in the weight-pulling group had muscle growth, especially on their forearms, and had no fat gain. However, exercise did not protect the mice from the effects of a high-protein diet on blood sugar control. Additionally, mice fed a high protein diet gained strength more quickly than those fed low protein, but there was no difference in the amount of weight the animals could pull despite the mice fed a high protein diet having bigger and larger muscles.
“We know that many people deliberately consuming high-protein diets or consuming protein supplements to support their exercise regimen are not metabolically unhealthy, despite the body of evidence showing that high-protein levels can have detrimental metabolic effects,” says senior author Dudley Lamming, Associate Professor of Medicine (Endocrinology) at the Department of Medicine, School of Medicine and Public Health, University of Wisconsin. “Our research may explain this conundrum, by showing that resistance exercise protects from high-protein-induced fat gain in mice. This suggests that metabolically unhealthy, sedentary individuals with a high-protein diet or protein supplements might benefit from either reducing their protein intake or more resistance exercise.”
