Does Protein Supplementation Prevent Muscle Disuse Atrophy and Loss of Strength?

Abstract

Recently there has been much interest in the use of dietary amino acids supplements to decrease the losses in muscle mass and strength observed after space flight or during aging using bed rest analogs. This interest persists even if the results have been mixed. Of the six published amino acid supplementation studies, three showed benefit, three did not. A recent study re-evaluating protein requirements in humans suggests that the official RDA is 41% underestimated. Interestingly, the three studies that showed benefits fed their test subjects a baseline protein level around the old RDA for protein. The three that did not show benefit gave the subjects a baseline protein intake higher than the new RDA. We suggest that the positive effects observed on protein metabolism might just reflect the benefits of adequate protein intake achieved during bed rest rather than a protective effect against bed-rest induced disuse. In conclusion, the efficiency of amino acid countermeasures for preventing the loss in protein mass during space flight or bed rest needs to be seriously questioned. These results extend to clinical situations such as serious illness and progress of aging in which physical inactivity is a significant component of the loss in muscle function.

Leucine partially protects muscle mass and function during bed rest in middle-aged adults

“…Similar positive results were also reported by Deutz et al (47), who used a very small amount (1.5 g twice daily, total of 3 g/d) of the leucine metabolite b-hydroxy-b-methylbutyrate to preserve muscle mass in older adults (60-76 y) during 10 d of bed rest. Although it is possible, or even likely, that additional protein or leucine-rich foods would also have a protective effect (55), continued efforts to develop efficient, mechanistically targeted, yet practical interventions may have broader clinical relevance. Our volunteers consumed w1.15 g protein • kg 21…”

“…Exceeding this moderate quantity of protein may be beneficial in many situations (e.g., flight analog studies, hypermetabolic patient populations) (55,56). However, it may be challenging or impractical for individuals with lower energy requirements, dietary restrictions, or satiety issues (57).…”

Protein Recommendations for Older Adults with Cirrhosis: A Review

“…Studies that did show benefit from protein supplementation had baseline diets of 0.6-0.8 g/kg/d and increased the protein given to 1-1.4 g/kg/d during the experimental phase. Studies with no benefit had baseline diet already at 1.0-1.2, further supporting the theory that an increased protein intake has a positive impact on older adults [50] . While it is evident that increased protein intake has a beneficial effect on older adults in general, the same may also hold true for individuals with liver cirrhosis.…”

A single session of neuromuscular electrical stimulation does not augment postprandial muscle protein accretion

“…Although our results demonstrate that NMES does not affect postprandial protein handling in healthy, active individuals, we cannot exclude that NMES may modulate postprandial protein handling in a more clinically compromised state, where anabolic sensitivity to food intake is further reduced (12,17,38,43), or in fact under situations where larger amounts or more anabolic dietary proteins are provided to older subjects. Obviously, the efficacy of NMES combined with nutritional support may be of particular relevance for older hospitalized patients, who are losing muscle partially due to low dietary protein intake (10,33,44). Furthermore, it should be noted that we assessed the effect of a single bout of NMES only, and we cannot rule out any synergistic effects of multiple, repetitive NMES sessions performed over time.…”