Protein supplementation, i.e. the addition of extra protein (generally in powder or bar form) to the protein intake from the diet, is generally observed in sports and particularly in resistance training. The main goal would be to improve the effects caused by training on muscle mass and strength. However, the scientific literature brings its share of contradictions and conclusions on the subject diverge. This is mainly due to the great diversity of the inclusion criteria of the different studies: age of the participants, level of training, total daily quantity of protein ingested, sources of protein, whether or not protein was taken after a workout, etc. But what could we really expect from it?
To answer this question, a team led by Prof. Stuart Phillips of McMaster University, Canada conducted a meta-analysis that included a larger number of randomized controlled studies that combined a strength training protocol with protein supplementation. They measured gains in fat-free mass or muscle cross-sectional area as a proxy for hypertrophy and gains in 1RM to quantify strength gains.
Thus, 49 studies were processed which included 1863 participants aged 35 ± 20 years. The training protocols lasted from 6 to 52 weeks, with 2 to 5 weekly sessions (1-14 exercises per session, 1-12 sets per exercise and 3-25 repetitions per set.
Regarding protein supplementation, between 4 and 106g of protein per day was administered to participants in the experimental group (42 ± 32 g/d for those under 45 years of age and 20 ± 18 g/d for those over 45 years of age), including 5-44g of protein post-workout on training days. In the end, the groups that were supplemented with protein obtained more protein than the control groups.
The main results of this meta-analysis show that protein supplementation increases the effects of weight training on muscle mass and strength. Regarding maximal strength, the 1RM increased by an average of 27 kg. The part related to protein supplementation represents about 2.5 kg, or 9%. This indicates that it plays a small role (but still present), and that to become stronger on an exercise, training remains the best stimulus. To get strong on an exercise, you must train specifically on that exercise.
Regarding changes for muscle mass, strength training alone resulted in an average 1.1 kg increase in fat-free mass, an increase in thigh muscle cross-sectional area of approximately 52 ± 30 mm², and an increase in the cross-sectional area of a muscle fiber of 800 μm². Protein supplementation resulted in an increase in dry mass of 0.30 kg, or 27%, an increase in thigh muscle cross-sectional area of 7.2 mm², or 14%, and an increase in muscle fiber cross-sectional area of 310 μm², or 38%. These effects were more pronounced in individuals with higher training levels, and in those with lower protein levels at the start of the study, but decreased with the age of the participants. Because advanced practitioners have less room for progression in training, they may have a greater need for protein than beginners to increase muscle mass. On the other hand, the scientific literature shows that with age, protein requirements are higher to generate equal muscle protein synthesis compared to young adults. And the results of this meta-analysis are not surprising because the protein intake of people over 45 years old was surprisingly low (20 ± 18 g/d).
Finally, post-workout protein intake did not influence the results on strength and muscle mass. This suggests that only the total daily amount would be important for muscle protein synthesis. In addition, when they pooled data from 42 studies involving 723 participants (under 45 and over 45) with daily protein intake ranging from 0.9 to 2.4 g of protein per kilogram per day, they found that above 1.6g/kg/d, no increase in muscle mass was observed. The 95% confidence interval ranged from 1.03 to 2.2 g/kg/d, suggesting that while 1.6 is ideal, higher amounts may be needed in some individuals under certain conditions to maximize gains in muscle hypertrophy.
Protein supplementation increases changes in strength (very modestly) and muscle mass when coupled with strength training. It is more effective in trained individuals than in untrained ones. However, if the dietary protein intake is sufficient (on average, 1.6g/kg/d), protein supplementation will be useless and its effects invisible. Protein supplementation in powder or bar form should only be considered once a diet has been thought out and implemented. If the protein intake from fish, meat, eggs, starchy foods, and other sources is sufficient, there is no need for supplements. Protein supplements have the advantage of being easily transportable, which makes them very practical when travelling and can be considered as an alternative for certain snacks.
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