Dietary protein consumption maximizes the anabolic response during resistance training (RT) by triggering muscle protein synthesis. Plant-based protein sources have lower levels of leucine, a key amino acid in this process, than animal-based protein sources. Do RT-induced muscular adaptations differ when supplementing plant-based proteins compared to animal-based proteins?
This nonrandomized trial investigated the effects of plant vs. animal protein on changes in muscle mass and strength in 38 physically active but untrained young men (aged 26 on average; 19 vegans and 19 omnivores).
The participants undertook 12 weeks of twice-weekly resistance training. Protein intake was assessed before the trial and was adjusted to 1.6 grams/kg of body weight/day met through supplemental protein (soy vs. whey) in addition to the habitual diet. The primary outcomes were muscle cross-sectional area (measured by ultrasound) and muscle strength (measured by leg press one-repetition maximum). The secondary outcomes were leg lean mass (measured by DXA) and muscle fiber cross-sectional area (measured by biopsy).
Both groups showed increases in leg lean mass, rectus femoris cross-sectional area, vastus lateralis cross-sectional area, and vastus lateralis muscle fiber type I and type II cross-sectional area. Strength was also increased in both groups, with no between-group differences for any of the variables.
Enrolling untrained participants is common in resistance training studies to ensure that the groups are homogenous, thus eliminating confounding variables. However, something to consider when interpreting these results is the phenomenon colloquially known as “newbie gains.” It’s been shown that previously untrained individuals show a greater muscle protein synthesis response to resistance training than trained individuals because new exercise causes more muscular stress and a stronger adaptive response.
One of the authors receives fees, equity, and grants from a variety of sources (a sports nutrition company, a biotech-pharmaceutical company, and various groups that promote dairy and potatoes.) This author also has two patents pending with the Exerkine Corporation.
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