madman
Super Moderator
Precise protein supplementation strategies for muscle improvement are still lacking. The timing or type of protein supplementation has been debated as a window of opportunity to improve muscle mass, strength, and physical performance. We conducted a network meta-analysis of randomized controlled trials with protein supplements and resistance training. PubMed, Web of Science, Cochrane Library, and SPORTDiscus databases were searched until May 1, 2023. We included 116 eligible trials with 4,711 participants that reported on 11 timing and 14 types of protein supplementation. Compared with placebo, protein supplementation after exercise(mean difference [MD]: 0.54 kg [95% confidence intervals 0.10, 0.99] for fat-free mass, MD: 0.34 kg [95% confidence intervals 0.10, 0.58] for skeletal muscle mass) and at night (MD: 2.85 kg [0.49, 5.22] for handgrip strength, MD: 12.12 kg [3.26, 20.99] for leg press strength) was most effective in improving muscle mass and strength, respectively (moderate certainty). Milk proteins (milk, whey protein, yogurt, casein, and bovine colostrum), red meat, and mixed protein were effective for gains in both muscle mass and strength (moderate certainty). No timing or type of protein showed a significant enhancement in physical performance (timed up-to-go test, 6-min walk test, and gait speed). Pre/post exercise and Night are key recommended times of protein intake to increase muscle mass and strength, respectively. Milk proteins are the preferred types of protein supplements for improving muscle mass and strength. Future randomized controlled trials that directly compare the effects of protein timing or types are needed. This trial was registered at International Prospective Register of Systematic Reviews as CRD42022358766.
Our study has several strengths. First, we used the method of NMA, which could summarize both direct and indirect comparisons to provide more robust evidence than conventional pairwise meta-analyses (Nikolakopoulou et al., 2018; Petropoulou et al.,2017). Second, we conducted a comprehensive literature search to include different timing or types of protein supplementation, thus,we could innovatively compare the effectiveness of different timing or types of protein supplementation on muscle mass, strength, and physical performance. Last, we rated the certainty of the evidence for each outcome using the GRADE approach and applied a minimally contextualized framework to summarize the results transparently and efficiently.
Several limitations need to be addressed. First, many of our results lacked support from direct comparative evidence. However, given the methodological strength of NMA (Nikolakopoulou et al.,2018), we believe our results could provide meaningful insights until further studies establish stronger evidence. Second, we only examined the effects of protein intake in adults undergoing RT; thus, it remains unclear the impact of the timing or type of protein supplementation in adults receiving endurance exercise training or without exercise training. Third, studies examining timing effects of protein ingestion often fail to rigorously equate total daily protein intake in the control group. Therefore, compared with the control group, the “protein timing” group has an inherent advantage of a larger daily total protein intake. Finally, among the factors that enhance muscle adaptation to RT, the total daily protein content is more important than time (Schoenfeld et al., 2013). Therefore, caution is necessary when interpreting studies aimed at investigating protein timing.
Conclusions
Overall, pre/post exercise and at night are the key recommended times of protein intake to increase muscle mass and strength,respectively. Animal-source proteins, especially milk proteins, are the preferred types of protein supplements for the improvement of muscle mass and strength. Given the large uncertainty in comparative estimates, future RCTs that directly compare the effects of different timing or types of protein supplementation on muscle mass, strength, and physical performance are of great requirement.
Our study has several strengths. First, we used the method of NMA, which could summarize both direct and indirect comparisons to provide more robust evidence than conventional pairwise meta-analyses (Nikolakopoulou et al., 2018; Petropoulou et al.,2017). Second, we conducted a comprehensive literature search to include different timing or types of protein supplementation, thus,we could innovatively compare the effectiveness of different timing or types of protein supplementation on muscle mass, strength, and physical performance. Last, we rated the certainty of the evidence for each outcome using the GRADE approach and applied a minimally contextualized framework to summarize the results transparently and efficiently.
Several limitations need to be addressed. First, many of our results lacked support from direct comparative evidence. However, given the methodological strength of NMA (Nikolakopoulou et al.,2018), we believe our results could provide meaningful insights until further studies establish stronger evidence. Second, we only examined the effects of protein intake in adults undergoing RT; thus, it remains unclear the impact of the timing or type of protein supplementation in adults receiving endurance exercise training or without exercise training. Third, studies examining timing effects of protein ingestion often fail to rigorously equate total daily protein intake in the control group. Therefore, compared with the control group, the “protein timing” group has an inherent advantage of a larger daily total protein intake. Finally, among the factors that enhance muscle adaptation to RT, the total daily protein content is more important than time (Schoenfeld et al., 2013). Therefore, caution is necessary when interpreting studies aimed at investigating protein timing.
Conclusions
Overall, pre/post exercise and at night are the key recommended times of protein intake to increase muscle mass and strength,respectively. Animal-source proteins, especially milk proteins, are the preferred types of protein supplements for the improvement of muscle mass and strength. Given the large uncertainty in comparative estimates, future RCTs that directly compare the effects of different timing or types of protein supplementation on muscle mass, strength, and physical performance are of great requirement.
