Review: Supplements boost lean leg muscle mass but show little benefit on strength

The review and meta-analysis of 20 randomised controlled trials (RCTs) assessed whether dietary supplements can prevent loss of muscle mass and strength during muscle disuse.

The authors from Jiangxi, China, concluded that while dietary supplements can improve lean leg mass, they are unlikely to affect muscle strength, muscle cross-sectional area (CSA), muscle fibre type distribution, peak aerobic capacity or muscle volume during muscle disuse.

They hypothesise: “This may be related to the fact that muscle strength is determined by many factors​, such as neuromuscular control and muscle mass.”

And they conclude: “Dietary supplements may be considered to maintain lean muscle mass when patients are unable to exercise during muscle disuse."

Significance ​

The temporary inactivity of muscles following injury or during disease recovery leads to muscle mass and functional decline, known as skeletal muscle atrophy (a decrease in muscle mass, occurring when protein degradation exceeds protein synthesis).

This includes​ a gradual reduction in muscle strength, lean muscle mass, muscle volume, aerobic capacity, cross-sectional area (CSA), atrophy of type I muscle fibres, and a transition from type I to type II muscle fibres. 

It can be accompanied by consequences such as reduced insulin sensitivity​, decreased basal metabolic rate​, and increased body fat mass​. 

While exercise is widely acknowledged as the best approach to maintaining and increasing muscle mass, patients often face restrictions that prevent them from engaging in physical activity. 

As a result, the authors of the new review note alternative methods, such as supplementation, could be necessary. 

The review ​

The review analysed RCTs from PubMed, Embase, Cochrane, Scopus, Web of Science, and CINAHL databases. The studies included had an average of 16.96 participants each.

Muscle strength and leg lean mass were used as the primary outcome indicators, while muscle cross-sectional area (CSA), muscle fibre type distribution, peak aerobic capacity, and muscle volume were used as secondary outcome indicators.

One study ​found that bed rest has a profoundly negative effect on skeletal muscle morphology and function in older adults and that supplementing with leucine, partially countered the loss of lean leg mass. 

Another study ​found that dietary supplementation with protein and essential amino acids, stimulated muscle protein synthesis, reducing muscle loss and promoting muscle growth during periods of immobilisation and ageing.

And another study​ found that improving protein quality without increasing total energy intake had the potential to counter some of the negative effects of bed rest in older adults.

Yet, some RCTs showed opposing results. 

One study​ concluded that whey protein plus potassium bicarbonate supplement did not attenuate atrophy and fibre-type transition during bed rest.

And another study​ found that nutrition countermeasure was not effective in offsetting lower limb muscle volume or strength loss.

The review notes all subgroup analyses of muscle strength showed that protein, amino acids, and other dietary supplements did not improve muscle strength during muscle disuse.

Yet, subgroup analyses of leg lean mass showed that the amino acid group significantly improved lean leg mass.

The authors note: “Our results are consistent with previously published systematic reviews​ of nutritional interventions for elderly or sarcopenic patients, where nutritional supplementation alone had no effect on muscle strength.”

Limitations​

The authors note that the review had some limitations.

They state: “The sample sizes of the included studies in the systematic review were relatively small, and the number of studies on outcome indicators such as CSA, muscle fiber type distribution, peak aerobic capacity, and muscle volume was relatively small.

“More RCTs with larger sample sizes are needed in the future to validate the effects of dietary supplements on these outcome indicators.”

Journal: Frontiers in Nutrition

https://www.frontiersin.org/articles/10.3389/fnut.2023.1093988/full#B17​

“Do dietary supplements prevent loss of muscle mass and strength during muscle disuse? A systematic review and meta-analysis of randomized controlled trials”

Authors: Hua Ye, Jia-Ming Yang, Yun Luo, Yi Long, Jia-Hong Zhang, Yan-Biao Zhong, Feng Gao and Mao-Yuan Wang