by Jeff S. Volek, Ph.D., R.D.
When it comes to promoting gains in muscle mass, there are many distinguishing features of whey protein that make it the standard of comparison. That doesn’t mean that other protein sources are worthless. In fact, most protein sources have the potential to produce similar effects to whey if used properly, including plant-derived proteins. For example, rice protein includes all the essential amino acids, but has lower amounts than whey of all three branched-chain amino acids. However, if consumed in a high enough dose, optimal levels of key amino acids such as leucine can be achieved.
A recent study sheds light on the benefits of using rice protein for active individuals. A group of healthy college-aged men with previous training experience participated in a weight training program (3 days per week) for 8 weeks. On training days after their workout one group consumed 48 grams of whey protein isolate and another group consumed 48 grams of rice protein isolate. After 8 weeks of training, both groups gained a similar and significant amount of lean body mass (5.5 to 7.0 pounds) as determined from dual-energy X-ray absorptiometry. Muscle thickness in the thigh and upper arm determined from ultrasound was increased to a similar extent in both groups. Muscle strength and power measurements were also increased in both groups. When analyzed, the whey contained 5.5 grams of leucine while the rice contained 3.8 grams of leucine.
Earlier research suggests that consuming 1.75-3.5 grams of leucine is a key factor when trying to maximize muscle protein synthesis. However, once this leucine level is reached, a protein’s ability to increase muscle protein synthesis effectively plateaus. Plant-based proteins contain about 6-8% leucine while animal-based proteins contain about 8-11% leucine.
The results of the study show that one could achieve the same lean mass and strength improvements with either whey or rice protein provided the dose of rice protein was high enough to provide an effective amount of leucine. The general trend from this study and other studies suggests that as the amount of protein consumed increases, the relative importance of its leucine content decreases. Other research shows taking free-form leucine with the other branched chain amino acids or with essential amino acids also helps to maximize muscle protein synthesis, but only in the presence of other amino acids.
The benefits of rice protein may be important to those with dairy allergies or to vegetarians.
Rice protein is also naturally rich in sulfur-containing amino acids (cysteine and methionine) which have important roles in maintaining antioxidant status. The bottom line – it takes about 36 grams of rice protein to equal the same leucine level as 24 grams of whey protein. However, once you get to 48 grams of either whey or rice protein, there seems to be no statistically significant benefit to using either one.