Does It Work?


Can whey promote muscle growth?


Whey is the liquid remaining after milk is curdled to make cheese or casein. Whey contains many components, including minerals, lactose and proteins. Whey protein can be separated from whey and has become a popular food supplement, especially among bodybuilders and others doing weight training.

Different proteins are made from different combinations of amino acids. Muscle protein is constantly being broken down and remade. For most people, these two processes are in balance and muscle mass remains fairly constant. Bodybuilders want to push this equilibrium towards increased muscle synthesis.

Muscle injuries and overtraining push the equilibrium in the opposite direction towards muscle loss. Muscle mass also decreases with age, especially after 50, which can have health implications. Muscle growth is also important in muscle-wasting diseases and during recovery from injuries. For both athletic and health reasons, interest has developed in how best to stimulate protein synthesis. Resistance exercise (weight lifting) has an important role in building muscle mass and strength, but diet is also very relevant.

A certain amount of protein is needed in a balanced diet. Amino acids are required to make muscle, and to carry out other specific functions in the body. Whey protein is particularly high in essential amino acids. One of these is leucine, required to initiate protein synthesis. Whey protein is easily digested, making its amino acids available quickly for muscle growth.


Numerous studies have demonstrated that consuming protein immediately after exercise leads to greater increases in muscle mass. Fewer studies have been done when protein is consumed before or during exercise, and these results are not consistent.

One limitation with all this research is that most studies have been conducted with young men, either well trained or untrained. Few studies have involved older adults, and very little research has been conducted with women. Therefore, the results obtained to date apply primarily to young men in a sports context.

Approximately 20-25g of protein appears to have the maximum effect in young men when consumed shortly after exercise. The type of protein is also important, with many studies finding that whey protein is one of the best. Several studies have compared dairy proteins with soy proteins. Whey protein (with exercise) consistently leads to greater muscle growth than soy or casein.

Some research suggests that whey protein that is partially or completely broken down to its amino acids might be more effective. The quicker a protein is digested, the sooner it impacts muscle growth. Whey protein’s leucine content is also very important to trigger protein synthesis. Leucine is also important in older adults as it appears to overcome the natural propensity for muscle breakdown.


Whey protein is usually tolerated well. Some people may have gastrointestinal problems, especially when taking large amounts a few times per day. In 2010, the US consumer protection organisation, Consumers Union, found slightly elevated levels of heavy metal contaminants in three of 15 protein powders, most containing whey protein. The organisation drew attention to weaknesses in US regulation of food supplements.


Consuming whey protein shortly after strenuous exercise has been shown to be beneficial for muscle growth, particularly for young men in a sports context. A smaller amount of research shows better muscle mass gains in older adults. All these studies combined strenuous exercise with whey protein. The more practical question of whether these gains in muscle mass lead to better sports performance or better health has not been addressed.

Many questions remain about the optimal way to use whey protein, or whether it helps all people. Some uncertainty remains as to how soon after exercise the protein should be consumed. Within one hour, or up to three hours, are most commonly suggested. No real consensus exists on how many days or weeks whey protein should be taken for maximum benefits.

In general, most research supports taking whey protein after strenuous resistance exercise for at least a few weeks to increase muscle mass.

Dónal O’Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University