While amino acids have long been touted by the fitness and bodybuilding communities for their muscle-building benefits, researchers from the University of Sydney say less attention had been paid to their possible negative side effects.
A new paper published in the journal Nature Metabolism examined the impact dietary BCAAs and other essential amino acids, such as tryptophan, had on the health and body composition of mice.
Mice were fed double the normal amount of BCAAs (200%), the standard amount (100%), half (50%) or one fifth (20%) for life. Mice that were fed 200% BCAAs increased their food intake (hyperphagia) resulting in obesity and a shortened lifespan.
“Supplementation of BCAAs resulted in high levels of BCAAs in the blood which competed with tryptophan for transport into the brain,” said Academic Director of the Charles Perkins Centre's and researcher from the School of Life and Environmental Sciences Professor Stephen Simpson.
“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. But serotonin does more than this, and therein lay the problem," he said.
“This then lowered serotonin levels in the brain, which in turn was a potent signal to increase appetite. The serotonin decrease caused by excess BCAA intake led to massive overeating in our mice, which became hugely obese and lived shorter lives.”
Secondary impact
The academics stressed that while long-term exposure to high BCAA diets les to hyperphagia, obesity and reduced lifespan, this was not due to elevated BCAA per se.
“Instead, this was due to a shift in the relative quantity of dietary BCAAs and other amino acids, notably tryptophan and threonine,” they wrote.
“Increasing the ratio of BCAAs to these amino acids results in hyperphagia and is associated with central serotonin depletion.
“Our data highlight a role for amino acid quality in energy balance and show that health costs of chronic high BCAA intakes need not be due to intrinsic toxicity but instead are a consequence of hyperphagia driven by amino acid imbalance.”
Source; Nature Metabolism
Volume 1, pages532–545 (2019)
“Branched-chain amino acids impact health and lifespan indirectly via amino acid balance and appetite control”
Authors: Samantha M. Solon-Biet, et al.