This is an excerpt from Plant-Based Sports Nutrition.
Considering Protein Supplements
Vegetarian and vegan athletes can meet their protein needs through diet alone. For convenience, however, many vegetarian athletes supplement their diets on occasion with protein-containing nutrition beverages or bars, which include soy protein isolate, pea protein,24 hemp protein, or whey protein. Many brands and varieties are available from both large pharmaceutical companies and small or local “ma and pa” businesses. Although this is fine on occasion, these food products should not replace real food and real meals, despite some companies' marketing ploys to convince you otherwise. While some evidence suggests that heavily processed isolated proteins are more rapidly digested and promote greater protein retention (at least over the short term), evidence that this affects the gain of muscle or strength in well-trained athletes in the long run does not exist. In fact, a recent study in rats found that the slower-absorbed milk protein casein nicely complemented the faster-absorbed whey protein in prolonging the muscle protein synthesis response to exercise,25 perhaps making milk protein in its natural form a better overall source of protein.
The idea of consuming isolated protein also interferes with my philosophy on healthy vegetarian eating because it ignores the way protein is typically consumed: in a mixed meal from whole foods. Even if there were a small grain of truth to the benefit of isolated-protein consumption, consistently giving up the pleasures of Thai-cooked tofu, savory split pea soup, or a bit of French cheese on a fresh baguette for a protein bar containing isolated soy, pea, or whey seems like a tragedy. These processed products serve their purpose but should not regularly replace the pleasures of eating real food. Many of us will also have to grapple with our acceptance of products such as the Impossible Burger that, because of genetic engineering, looks, tastes, and nearly bleeds like real meat.16,26
Indeed, adequate protein—which is easily provided by a vegetarian diet—is necessary for gaining muscle strength and muscle mass through athletic training.