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Higher doses of plant proteins may provide the right amount of essential amino acids for muscle growth.
Writing in Nutrition Journal, researchers from the United States and Brazil say similar muscle benefits can be had with rice protein and whey protein-when they are taken in high doses.
In clinical studies on athletes, plant proteins have, on occasion, failed to exhibit the same muscle-maintaining benefits as dairy proteins. This is often attributed to lower levels of essential amino acids in plant proteins. One such amino acid is leucine, which limited data suggests can encourage muscle protein synthesis more than other amino acids. In low doses, plant proteins reportedly contain just 6–8% leucine, which is lower than what’s found in equivalent doses of dairy proteins.
Researchers at the University of Tampa have now found that a high dose of rice protein can support muscle growth and maintenance as much as whey protein, post-workout. In a study on 24 college-age males, subjects were assigned to consume 48 g of rice or whey protein isolate immediately after resistance training (three days weekly, for eight weeks). By eight weeks, no differences were observed in perceived recovery, soreness, or readiness to train. Lean body mass, muscle mass, strength, and power all increased, and fat mass decreased-in all subjects. The lack of a difference all of these parameters is, the researchers suspect, because of an adequate, 8% content of leucine in the rice protein.
“The collective findings of our study and others suggest that as the amount of protein consumed increases, the importance of the relative leucine content of the protein diminishes,” wrote the authors of the study.
The researchers add that leucine and protein appear to have plateaus whereby increasing protein content will not result in further increase of muscle protein synthesis. This would explain the similar results with both proteins, since the high dose of whey protein contained significantly more leucine (and other amino acids) than the rice protein.
The researchers believe this is the first human clinical trial to explore higher doses of plant and animal proteins in resistance-trained athletes. Growing Naturals provided rice protein isolate for the study.