By Sally Robertson, B.Sc.

Reviewed by Kate Anderton, B.Sc. (Editor)

New research from the University of Sydney suggests that excessive intake of branched-chain amino acids (BCAAs) in the form of pre-mixed protein powders, shakes and supplements may do more harm to health than good.

Amino acids have long been praised by bodybuilders and fitness fanatics for their muscle building properties and have even been marketed as the magic ingredient in many “high-protein, low-carbohydrate” diets.

What are BCAAs?

When proteins are broken down during digestion, they release amino acids, which are used to create the proteins that make up every cell, tissue and organ in the body. Amino acids are broadly divided into two classes: non-essential amino acids, which can made by the body, and essential amino acids, which are not produced by the body and need to be obtained through diet.

There are nine essential amino acids, namely histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. BCAAs are the essential amino acids leucine, isoleucine, and valine, which are found in protein-rich foods such as red meat, dairy, chicken, fish and eggs. For vegans, nutritional sources of BCAAs include lentils, nuts, and soy proteins.

Supplements that contain BCAAs are popular with athletes and bodybuilders for their muscle-building benefits, including increased muscle growth and improved performance.

Do BCCAs improve muscle mass?

In a 2013 study by researchers at Chonnam National University, Korea, 26 college-age males were randomly assigned to take either a BCAAsupplement or a placebo. The cohort was then examined for the effects of BCAA administration on fatigue substances, muscle damage substances and energy metabolism substances after engaging in endurance exercise.

The researchers found that BCAA supplementation improved energy metabolism and lowered levels of muscle damage substances, leading them to conclude that BCAA can improve exercise performance.

‘Detrimental effects for health’

Although BCAAs are highly effective at growing muscle, new research from the University of Sydney’s Charles Perkins Center suggests that when taken in excess, BCAAs can have detrimental effects later in life.

Excessive consumption of any protein is not ideal and excessive intake of protein powders or shakes could even be dangerous, say the researchers.

As reported in the journal Nature Metabolism, Solon-Biet and colleagues found that although BCAAs exert muscle-building benefits, excessive intake may reduce lifespan, increase appetite, lead to weight gain and have a negative impact on mood.

For the study, the team used a mouse model to examine the health effects of consuming BCAAs and other important essential amino acids such as tryptophan. The animals were divided into four groups: those who were fed the standard amount of BCAAs, twice the standard amount, half the standard amount and one-fifth of the standard amount over the course of their lives.

How BCAAs affect mood

BCAA supplementation resulted in high levels of BCAAs in the blood, which competed with tryptophan for transport into the brain, explains co-author Professor Stephen Simpson.

Both amino acids try to access the brain, but once there, exert different effects. Tryptophan is the sole precursor for the hormone serotonin, which is often referred to as the “happiness” hormone, promoting sleep and enhancing mood.

“But serotonin does more than this, and therein lay the problem,” says Simpson.

When blood levels of BCAAs are high, they “steal” tryptophan’s place in the brain, lowering levels of serotonin, which can negatively impact mood.

However, serotonin is not only a mood enhancer – it is needed to regulate appetite.

The lowered serotonin level due to excess BCAA intake in the mice that were fed twice the standard amount caused the animals to massively overeat and become obese, which shortened their lifespans.

Dietitian and nutritionist Dr. Rosilene Ribeiro, also from the University of Sydney, recommends following a diet that contains a wide range of proteins.

People should consume a range of protein  sources to ensure that a variety of essential amino acids is consumed through a healthy and balanced diet that is rich in fiber, vitamins, and minerals: