The effect of protein supplementation on muscle mass and strength

Resistance training is a type of exercise characterized by skeletal muscles (the muscles responsible for voluntary movement) being forced to contract against some form of external load. This unique type of exercise has important health benefits that are mediated, in part, through its ability to increase muscle mass and strength^[1]. Not only does skeletal muscle help you look good naked, but it plays an important role^[2] in the prevention of many diseases such as obesity, type 2 diabetes, and osteoporosis.

Protein supplementation is a widespread practice among people who partake in resistance training, be they athletes or average. The idea is that protein supplementation will enhance training-induced gains in muscle mass and strength. Although a single exercise session^[3] increases muscle protein synthesis for up to 48 hours, overall muscle protein balance is negative without nutritional intervention. Consuming protein after training has been shown^[4] to shift muscle protein balance from a negative to a positive state.

Several meta-analyses^[5] and systematic reviews^[6][7] have reported that protein supplementation leads to increased muscle mass and strength. The largest meta-analysis^[7] to date was conducted in 2012 and included 22 randomized controlled trials. It reported that protein supplementation significantly enhanced muscle mass and strength in both young and older adults. However, a recent systematic review^[8] has challenged this conclusion, arguing that the effect of protein supplementation on muscle mass and strength is inconsistent and any benefit is minor, at best. This review was not a meta-analysis though, meaning that there are about five years of data that have not been evaluated quantitatively.

The study under review is a meta-analysis investigating the impact of protein supplementation on several important resistance training outcomes, including muscle mass and strength. It contains more than double the number of studies included in the previous meta-analysis from 2012, including studies published in the last five years that the other meta-analysis did not include.

Skeletal muscle plays an important role in health and resistance training, the go-to method for increased muscle mass and strength. The benefit of protein supplementation for enhancing resistance training-induced adaptations, while supported previously, has recently been questioned. The study under review is an updated meta-analysis investigating the effect of protein supplementation on muscle mass and strength.