How deadly are protein shakes?
No, it's not an April fools day joke. A small battalion of health writers is sincerely convinced that protein shakes make athletes depressed, fat and less healthy. According to them, researchers from the University of Sydney have demonstrated that protein shakes shorten your life span. We read the Australian study, and are, ehm, underwhelmed...
From bad to worse
No, protein shakes don't make you depressed. Protein shakes will also not cause you to die prematurely. That is not the scope of the research that Samantha Solon-Biet and her colleagues have published in Nature Metabolism. But health writers who have not read Solon-Biets study and rely on the press release about that study [sciencedaily.com April 30, 2019] may get a wrong idea of Salon-Biet's research.
The Australian animal study is about the effect of replacing intact proteins with hefty doses of BCAAs. However, the press release from the University of Sydney is not clear about that.
Because the press release also says that 'BCAAs are included in all sorts of supplements for athletes', even the excellent Medical News Today website lost track. "Muscle building protein shakes may be threatening health," headlined the website. [medicalnewstoday.com 3 May 2019]
If Medical News Today fails, then you can't blame the Daily Mail for running crazy. "Stop drinking protein shakes!", The British tabloid wrote above the article about the Australian study. [dailymail.co.uk 30 April 2019]
It is absolutely wrong. But it is catchy.
The researchers gave a group of mice lifelong standard feed that consisted of 18 percent amino acids . The amino acids were part of casein.
Three other groups of mice received less casein and loose amino acids instead. Another group received 50 percent of the amount of BCAAs present in the standard diet , there was a group that received 20 percent of the standard amount of BCAAs  - and there was also a group of mice that received 200 percent of the amount of BCAAs in the standard feed .
All groups of test animals received food consisting of 18 percent amino acids, in the form of protein or in the form of free amino acids.
More information about the diet of the mice can be found here.
The 200 group lived significantly shorter than the other groups, the researchers discovered. If these mice had been humans, they would have kicked about 32 percent of their proteins out of their diet, and replaced them with dozen of grams of free-form BCAAs.
Above you can see how the replacement of intact proteins with BCAAs deteriorated health. The mice in the 200 group became fatter. They ate more than the mice in the other groups.
When the researchers gave the mice 200 food and limited their intake [Calorie-restricted], the negative effect on their life span disappeared.
Because the mice in the 200 group overate, their sensitivity to insulin and the concentration of triglycerides in their blood decreased. When the researchers made sure that the mice in the 200 group could only eat a limited amount, those negative health effects disappeared.
The appetite-enhancing effect of BCAAs largely disappeared when the researchers also gave mice with 200-feed extra tryptophan. The antidepressant fluoxetine worked even better.
"Supplementation of BCAAs delivered in high levels or BCAAs in the blood which competed with tryptophan for transport into the brain", research leader Stephen Simpson explains in a press release. [sciencedaily.com April 30, 2019]
"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."
"This then lowered serotonin levels in the brain, which in turn was a potential 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."
This research says nothing about protein supplements. It also says nothing about the way athletes use BCAAs. However, the study shows what can happen if you take a good portion of the intact proteins - in protein shakes, but also in meat, fish, eggs and soy - out of your diet and replace them with dozens of grams of BCAAs.
Eur J Sport Sci. 2019 May 9:1-8. doi: 10.1080/17461391.2019.1611932. [Epub ahead of print].
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