New research suggests that limiting the consumption of protein building blocks known as branched-chain amino acids could be an alternative way to shed excess weight to restricting calories, which many people trying to combat diabetes and obesity find hard to do.
After studying their effects in mice, scientists at the University of Wisconsin-Madison conclude that branched-chain amino acids (BCAAs) are important for metabolic health in obese animals.
"We've identified an unanticipated role for dietary BCAAs in the regulation of energy balance," explains co-principal investigator Dudley Lamming, who works as an assistant professor in the Division of Endocrinology, Diabetes and Metabolism.
In a study paper that was recently published in The Journal of Physiology, he and his team suggest that, if the findings translate to humans, then "specifically reducing dietary BCAAs" might be an effective way to treat obesity and insulin resistance.
BCAAs' crucial role in vital body functions
BCAAs are a group of essential amino acids that includes leucine, isoleucine, and valine. Essential amino acids are those that the body needs to get from food sources, as it cannot make them to a level that is sufficient for healthy growth.
Red meat and dairy products are rich dietary sources of BCAAs. People who follow vegan diets can also get them from vegetable sources such as soy protein.
In the body, BCAAs are important for producing neurotransmitters, which are the chemical messengers of the brain and central nervous system.
'Rapid reversal of diet-induced obesity'
In their study, Prof. Lamming and his team put pre-diabetic, obese mice on a Western diet that was low in leucine, isoleucine, and valine but otherwise not restricted in amount of calories, fat, and sugar. The mice could eat as much of this low-BCAA food as they desired.
During the study, the team monitored the animals' energy usage, glucose metabolism, and body weight and composition.
The results showed that — despite being able to eat as much high-fat and high-sugar food as they wanted — the mice on the low-BCAA diet showed a dramatic improvement in metabolic health.
The researchers note that reducing BCAAs in the diet "rapidly reverses diet-induced obesity" and improves glucose control in diet-induced obese mice.
"Most dramatically," the study authors add, "mice eating an otherwise unhealthy high-calorie, high-sugar Western diet with reduced levels of BCAAs lost weight and fat mass rapidly until regaining a normal weight."
Increased energy use, not increased activity
The team suggests that an important factor in the "normalization of weight" was that it came about not as a result of "caloric restriction or increased activity," but as a result of increased energy use that involved "the energy balance regulating hormone FG21."
The weight loss witnessed was also "accompanied by a dramatic improvement in glucose tolerance and insulin resistance."
The study confirms an increasing amount of evidence suggesting that protein metabolism is as important in insulin resistance as fat and carbohydrate metabolism.
The study authors write that their findings "suggest that specifically reducing dietary BCAAs may represent a highly translatable option for the treatment of obesity and insulin resistance."
However, previous evidence on the effect that BCAAs specifically have on insulin resistance is conflicting and has caused some experts to remark that "species difference" might be a factor.
This would suggest, therefore, that the results of this study should be treated with caution until the question of "if the results translate to humans" is resolved.
"Our results also suggest that the specific amino acid composition of dietary protein — not just how much protein we eat — regulates metabolic health."
Prof. Dudley Lamming