Doubling protein intake while exercising protects against muscle loss, promotes fat loss
Consuming twice the recommended daily allowance of protein while adhering to a diet and exercise plan prevents the loss of muscle loss and promotes fat loss, scientists from the US Army Research Institute of Environmental Medicine have found.
However, the research, which was published in the September 2013 issue of The FASEB Journal, showed that tripling the recommended daily intake of protein failed to provide additional benefits.
Researchers assigned 39 young men and women controlled diets for 31 days. The diets provided protein at three different levels: the US RDA, twice the US RDA and three times the US RDA.
Participants were given adequate total calories to maintain constant body weight for the first 10 days to allow their metabolism to adapt to the dietary protein level, and then for the following three weeks, weight loss was induced by restricting the total calories and increasing daily exercise sufficiently to elicit an average two-pound weight loss per week. Body composition and measurements of muscle protein metabolism were performed at the end of both the stable weight maintenance and weight loss phases of the study.
The study participants lost body weight during the weight loss phase of the research, regardless of their protein intake. Researchers found the proportion of weight loss due to restriction in fat-free mass was lower and the loss of fat mass was higher in those receiving twice the RDA and three times the RDA compared with those who were eating the RDA.
The anabolic muscle response to a protein-rich meal during the weight loss phase was not different from the stable weight phase for both participants eating twice the protein RDA and three times the RDA. Participants eating the protein RDA, however, exhibited muscle loss during the weight loss phase. The researchers said these results, in which there were no difference between muscle loss for those eating twice and three times the RDA, showed that there were limits to the protective effect of extra protein.
“This study essentially confirms what body builders have shown us for a long time – a high protein diet helps prevent muscle loss when trying to lose fat,” said Gerald Weissmann, MD, Editor-in-Chief of The FASEB Journal. “Although eating a well balanced diet is still necessary for health and weight maintenance, upping one’s protein intake when dieting might be a useful tool in the short term,” he said.
Researchers said they hoped the findings would be part of any discussion by the Institute of Medicine for the updated Dietary Reference Intakes on protein.
“We believe that the recommended daily allowance (RDA) for protein should be based on a level to optimise health, as well as prevent deficiencies, and our data demonstrate a potential inadequacy in the current RDA for sparing muscle mass during weight loss, which may affect a significant portion of the population,” said Stefan M. Pasiakos, Ph. D, a researcher involved in the work from the Military Nutrition Division at the US Army Research Institute of Environmental Medicine.