Excessive Intake of Protein for Bodybuilding May Impact Health and Lifespan

Study in mice shows that excessive long-term intake of dietary protein containing high amounts of branched-chain amino acids (BCAAs) can result in imbalance in amino acids and appetite control. This affects metabolic health and causes reduced lifespan.

A healthy diet should contain balanced amounts of macronutrients (protein, carbohydrate and fats), fibres, vitamins and minerals. Numerous researches have focused on the importance of balanced amounts of dietary protein, fats and carbohydrates for our good health. Any imbalance in proportions of these macronutrients in our diet is known to cause ill-health.

Protein is a complex macromolecule composed of amino acids. There are 20 amino acids, of which nine are essential which can enable the body to make the remaining 11. The branched-chain amino acids (BCAAs) are made up of three of the nine essential amino acids – leucine, isoleucine and valine. Muscles, the main building block of the body are mainly composed of proteins. BCAAs are broken down in muscle, have high calories and are consumed for muscle mass they provide. BCAAs are present in protein foods like red meat, eggs, beans, lentils, soy protein etc. and are also commonly present in bodybuilding protein supplements consumed after exercise or workout. Not enough studies have been done to evaluate the adverse effects of consuming excessive BCAAs. Their long-term effects on health and lifespan are still unknown.

In a study published in Nature Metabolism on April 29, 2019 researchers aimed to determine how manipulating long-term dietary BCAAs might have an effect on health and lifespan. In their experiments conducted on mice, the animals consumed for their entire life span either (a) normal amount of BCAAs i.e. 200 percent (b) half the amount i.e. 50 percent or (c) one fifth of the amount i.e. 20 percent. Alongside, mice were given isocaloric, fixed amounts of other macronutrients – carbohydrates and fat. Intake of excessive BCAAs led to high amounts of BCAAs in blood and this appeared to block transport of another non-BCAA tryptophan to the brain. Tryptophan is the sole precursor of hormone serotonin which has mood elevating effects and thus is crucial for promoting sleep. Once tryptophan was blocked from reaching the brain, this led to depletion of central serotonin levels resulting in excessive eating (or hyperphagia) in mice primarily due to the amino acid imbalance via increased ratio of BCAAs:non-BCAAs. Thus, mice overconsumed food (both total energy and BCAAs) – also called compensatory feeding – resulting in increased body weight and fat mass thus making them obese and shortening their lifespan.

This study shows that the relationship between increased levels of circulating BCAAs in blood and adverse health outcomes do not appear to be linked to intrinsic BCAA toxicity or harmfulness. The relationship was due to the interactions between BCAAs and other important amino acids and this was what led to extreme hyperphagia. Results suggest that taking high amounts of dietary BCAAs for long-term along with fixed amounts of other macronutrients can result in hyperphagia driven by amino acid imbalance and affect metabolic health and reduce lifespan. Although high amounts of BCAAs can occur in both metabolically healthy and unhealthy mice. Therefore, BCAA alone cannot be the only biomarker for metabolic health.

The current study re-establishes the importance of consuming a healthy balanced diet containing variety of macronutrients, fibres, vitamins and minerals and restricting intake of unneeded supplements.



Solon-Biet SM et al. 2019. Branched-chain amino acids impact health and lifespan indirectly via amino acid balance and appetite control. Nature Metabolism.

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