Muscle-building protein shakes linked to weight gain, depression in new study

New research from the University of Sydney suggests protein shakes may not be as safe as you think.

According to the study, published last week in the journal Nature Metabolism, consuming high levels of certain amino acids commonly found in commercially available whey protein shakes may lead to increased food cravings, weight gain, depression and shorter lifespans.

» RELATED: These protein powders are toxic to your health, study says

For the study, researchers tested the effects of three common branched-chain amino acids (leucine, valine and isoleucine) in mice that typically feed on foods high in carbohydrates and low in fats. BCAAs are known to improve muscle mass and exercise performance.

The mice were fed double the normal amount of BCAAs, the standard amount, half or one-fifth for life.

They found the rodents that ingested double the normal amount of BCAAs had high levels of the three amino acids in their blood, which in turn hampered the function of alpha amino acid tryptophan.

» RELATED: 5 tips for your homemade smoothie that will help you lose weight

"Tryptophan is the sole precursor for the hormone serotonin, which is often called the 'happiness chemical' for its mood-enhancing effects and its role in promoting sleep," researcher Stephen Simpson said in a university article.

When the mice consumed a high-BCAA diet, Simpson and his team found lower-than-normal serotonin levels in the brain. The low serotonin levels led to massive overeating and ultimately, shorter lives.

According to Harvard Health, research also supports the idea that some people with depression have reduced serotonin transmission. And low levels of a serotonin byproduct have previously been linked to a higher risk for suicide.

“What this new research has shown is that amino acid balance is important – it’s best to vary sources of protein to ensure you’re getting the best amino acid balance,” co-author Samantha Solon-Biet said.

Here are some suggestions from University of Sydney nutritionist Rosilene Ribeiro:

• Vary your protein sources so you get a variety of essential amino acids.
• BCAAs are essential amino acids found in protein. Consider getting your BCAAs from red meat, dairy, chicken, fish or eggs. Vegetarians can turn to beans, lentils, nuts and soy proteins.
• Include foods rich in tryptophan, such as seeds, nuts, soy beans, cheese, chicken, turkey and crocodile.