Is losing a significant amount of muscle mass part and parcel of losing weight through exercise and diet? A new report appearing in the September issue of The FASEB [Federation of American Societies for Experimental Biology] Journal (2013; , 3837-47) challenges this belief.
Scientists showed that consuming twice the Recommended Dietary Allowance (RDA) of protein while adhering to a diet and exercise plan prevented loss of muscle mass and promoted fat loss. Tripling the RDA of protein, however, failed to provide additional benefits. “In summary, we determined that consuming dietary protein at levels exceeding the RDA may protect fat-free mass during short-term weight loss,” said the authors.
“It is our hope that the findings from this well-controlled study will be discussed and cited by the Institute of Medicine for the updated Dietary Reference Intakes on protein,” said Stefan M. Pasiakos, PhD, a researcher from the Military Nutrition Division at the U.S. Army Research Institute of Environmental Medicine in Natick, Massachusetts, who was involved in the work. “We believe that the RDA for protein should be based on a level to optimize health, as well as prevent deficiencies, and our data demonstrate a potential inadequacy of the current RDA for sparing muscle mass during weight loss, which may affect a significant portion of the population.”
- In a randomized, controlled trial lasting 31 days, Pasiakos and colleagues provided 39 adults with dietary protein at three different levels: (1) the U.S. RDA; (2) twice the U.S. RDA; and (3) three times the U.S. RDA.
- Volunteers were given enough 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 3 weeks, weight loss was induced by restricting total calories and increasing daily exercise sufficiently to elicit an average 2-pound-per-week weight loss.
- All meals were prepared and administered by research staff, and exercise was highly controlled. 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.
Results of this study demonstrated that there are limits to the protective effect of extra protein. As such, these data suggest an optimal, and perhaps maximal, level of protein for young, active adults who may undergo short-term periods of intentional or unintentional weight loss.
Editor’s Note: Be sure to read this month’s Nutrition column, “Protein Today: Are Consumers Getting Too Much of a Good Thing?” by Martina M. Cartwright, PhD, for a balanced view on the effects of protein overconsumption.