Can You Gain Muscle While Only Drinking Soy Milk?

Milk is generally considered to be one of the most useful foods for the task of gaining muscles. It contains a high amount of protein because of its origin as an animal product. Some bodybuilders drink as much as 1 gallon every day. However, some controversy surrounds the question of whether milk replacements such as soy milk offer the same benefits. Soy can contribute to a balanced diet and provides nutrients that support muscle growth, but it's not as beneficial as dairy milk, and it should never be the only food in your diet.

Soy milk is an alternative to milk from animals. It is an emulsion of oil, water and protein produced by soaking dry soybeans and grinding them in water. Soy beans are a type of legume. It has about the same amount of protein as regular cow milk, which contains 3.3 percent total protein.

Muscle is made out protein, which helps the mechanisms of the fiber to fulfill their contractile obligations. Protein is made up of chains of amino acids connected by special bonds. Twenty amino acids can be found in the human body, nine of which the body cannot make on its own and therefore must obtain through diet. Protein consumption is absolutely critical. You must also replace the amino acids through the diet that are lost every day. Milk contains all nine essential amino acids required by humans. So does soy milk, though not necessarily in the same proportions. Soy lacks the proteins whey and casein found in cow milk.

Some debate has arisen over supposed enzyme inhibitors in soy milk. Enzymes are special proteins that facilitate and expedite chemical reactions. This is critical for the breakdown of certain molecules during digestion. Enzyme inhibitors tend to block the uptake of trypsin and other enzymes, which the body needs for the digestion of protein. Reduced protein digestion and chronic deficiencies in amino acid uptake can result. However, popular nutritionist author John Robbins claims that this effect is diminished in actual soy foods, and the digestibility of protein in soy milk is similar to other kinds of foods.

A study conducted by researchers at McMaster University's Department of Kinesiology, which was published in the American Journal of Nutrition, compared the gain of muscle protein in young men after heavy strength training followed by consumption of equivalent amounts of either skim milk or soy milk. The study found that those who drank 2 cups of skim milk after workouts gained twice as much muscle in 10 weeks than those who drank only soy. Other studies from French researchers have corroborated these findings.

Stuart Phillips, associate professor of kinesiology and researcher in the study, explained the results: "This is an interesting finding, since soy and milk proteins are considered to be complete proteins that are basically equivalent from a nutritional standpoint. Our findings clearly show that milk proteins are a superior source of protein in producing muscle mass gains in response to weightlifting." Researchers haven't determined for sure the exact mechanism that leads to lower gains. It could be the enzyme inhibitors, or it could be the lack of whey and casein.