The efficacy of diet-induced weight loss interventions depends, in part, on the retention of lean body mass during periods of energy restriction. Studies suggest that muscle loss during energy restriction may suppress muscle protein synthesis. For this reason, there are compelling reasons to develop targeted dietary interventions aimed at minimizing muscle loss during diet-induced energy restriction specifically in post-menopausal women who are at an enhanced risk of losing muscle mass and strength. The dose-response of muscle protein synthesis, to protein intake, with or without resistance exercise, is well characterized during energy balance, but remains unclear under conditions of energy restriction in clinical populations.
To bridge this knowledge gap, Hansen (Aarhus University, Denmark) and colleagues conducted a study to determine the dose-response of muscle protein synthesis to ingested whey protein following short-term diet-induced energy restriction in overweight, postmenopausal women at rest and postexercise. Forty middle-aged, overweight, postmenopausal women were randomly assigned to 1 of 4 groups. Three groups underwent a 5-day energy-restricted dietary intervention and one group continued their habitual energy balanced diet. On day 6 participants performed one-legged resistance exercises before ingesting either 15, 35, or 60 grams of whey protein. The fourth group ingested 35 grams of whey protein after 5 days of an energy balanced diet. Muscle protein synthesis was determined by measuring the myofibrillar fractional synthetic rate.
Myofibrillar fractional synthesis was greater in women consuming 35 and 60 grams of whey protein compared to those consuming 15 grams of whey protein. There were no differences between groups consuming 35 and 60 grams of whey protein. The rate of myofibrillar fractional synthesis was greater in the fed and fed-exercising groups, but no differences were detected between the fed and fed-exercising conditions. No differences in myofibrillar fractional synthesis were observed between the energy balance (35 grams of whey protein) and energy restricted (35 grams of whey protein) groups.
A 35-gram dose of whey protein, ingested with or without resistance exercise, was sufficient to stimulate a maximal acute response of myofibrillar fractional synthesis following short-term energy restriction in overweight, postmenopausal women, and thus may provide a per serving protein recommendation to mitigate muscle loss during a weight loss program. Thus, a practical recommendation for this important clinical subpopulation is to ingest 35 grams of high-quality protein per meal during a weight loss program.
However, it cannot be ruled out that the dose needed to maximize muscle protein synthesis is lower than 35 grams (but higher than 15 grams). Long-term studies are needed to determine if meal doses of 35 g protein reduces loss of muscle mass during energy restriction.
References
Larsen MS, Witard OC, Holm L, Scaife P, Hansen R, Smith K, Tipton KD, Mose M, Bengtsen MB, Lauritsen KM, Mikkelsen UR, Hansen M. Dose-Response of Myofibrillar Protein Synthesis To Ingested Whey Protein During Energy Restriction in Overweight Postmenopausal Women: A Randomized, Controlled Trial. The Journal of Nutrition, Volume 153, Issue 11, November 2023, Pages 3173-3184, doi.org/10.1016/j.tjnut.2023.08.011.
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