Is Your Protein Shake Making You Fat?

Will Brink Brinkzone

If you were to read the articles going around on the ‘net currently based on a mouse study, you’d think there was something to worry about! Per usual, the truth is far more complicated. Researchers found at high intakes (200% of normal intakes) of branched-chain amino acids (BCAA’s) caused mice to overeat, get fat, and live shorter life spans. Various poorly written articles looking for some clickbait, with completely misleading titles such as “Stop drinking protein shakes! Bulk-up beverages may lead to weight gain, depression and shorter life spans, study suggests” have caused much confusion.

I will attempt to clear all that up here. The study published in the Nature Metabolism (2019) found that at the highest doses of BCAA intakes, it lead to hyperphagia (abnormally increased appetite) and weight gain and ill healthy for the mice. Per usual, we are not mice, but the study is still worth discussing. What they discovered was the BCAA’s at high doses caused an amino acid imbalance, preventing the amino acid tryptophan from doing its job in the brain. Professor Stephen Simpson, Director of the Charles Perkins Centre’s and researcher from the School of Life and Environmental Sciences, summarizes it nicely:

“Supplementation of BCAAs resulted in high levels of BCAAs in the blood which competed with tryptophan for transport into the brain. 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. Branched-chain amino acids impact health and lifespan indirectly via amino acid balance and appetite controlThis 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.“

Bottom Line

Truth be known, per my writing, vids, etc, I have never been a big fan of isolated BCAA’s, as covered in my now free massive Ebook, Bodybuilding Revealed, as well as this site via articles and vids. A quality protein with well balanced amino acid (AA) profiles, such as whey, will cover BCAA requirements of active people while supplying other AA’s in ratios that are beneficial overall. Speaking of whey, it has the highest BCAA content of any protein, yet studies suggest a major benefit to weight loss and health, improves mood, including appetite regulation!

Is it possible a person could ingest enough isolated BCAA’s over a long enough period of time to experience what those mice did? Hypothetically, sure. How large a dose in a human to experience that? Unclear. Should people worry about their post workout shakes? No. This study simply confirms a rather “no duh” conclusion known for decades, which is eating a range of protein sources is best for overall health and athletic endeavors. Should you get the majority of your protein from any one source? No. The study itself is interesting, albeit of very limited utility and relevance to free living humans who may ingest a protein shake or two per day. Per usual, it’s the lay media taking the results wildly out of context. No, I don’t recommend people supplement with additional BCAA…

Nature Metabolism (2019)


Elevated branched-chain amino acids (BCAAs) are associated with obesity and insulin resistance. How long-term dietary BCAAs impact late-life health and lifespan is unknown.

Here, we show that when dietary BCAAs are varied against a fixed, isocaloric macronutrient background, long-term exposure to high BCAA diets leads to hyperphagia, obesity and reduced lifespan. These effects are not due to elevated BCAA per se or hepatic mammalian target of rapamycin activation, but instead are due to a shift in the relative quantity of dietary BCAAs and other amino acids, notably tryptophan and threonine.

Increasing the ratio of BCAAs to these amino acids results in hyperphagia and is associated with central serotonin depletion. Preventing hyperphagia by calorie restriction or pair-feeding averts the health costs of a high-BCAA diet. 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.