People who want to grow larger muscles spend more than 10 million dollars a year on whey protein shakes. A new study on mice shows that these whey protein shakes contain very high levels of branched-chain amino acids (BCAAs), which can reduce certain brain hormones to increase risk for obesity and premature death (Nature Metabolism, May 1, 2019;1:532–545).
All proteins are made up of 20 building blocks called amino acids. Humans need to get only nine of the amino acids from the food they eat because they can make the other 11 amino acids from those nine (called the essential amino acids). Of the nine essential amino acids, three are called BCAAs: leucine, valine, and isoleucine. The BCAAs are the only amino acids that can be converted into sugar, and in large amounts they can cause high blood sugar levels, which increase risk for obesity and diabetes (J Diabetes Investig, 2015 Jul; 6(4): 369–370).
The Study Researchers fed double the usual amount of BCAAs in whey protein to mice that normally ate a high carbohydrate, low-fat diet. The mice fed the high-BCAA diet developed very high blood levels of the three BCAAs (leucine, valine, and isoleucine) that competed with another amino acid called tryptophan to enter into the brain. Tryptophan is essential to make an important brain hormone called serotonin that makes you feel happy and feel full when you eat (Curr Drug Targets, 2005;6:201–213). The high levels of BCAAs dropped brain levels of serotonin significantly, which caused the mice to overeat so they became obese and died prematurely.
Previous studies have shown that high levels of BCAAs increase fat deposition in the body (Nat Chem Biol, 2016;12:15–21). High levels of BCAAs increase insulin resistance (Metab Syndr Relat Disord, 2017;15:183–186) to increase risk for developing diabetes (Int J Epidemiol, 2016;45:1482–1492). Decreased consumption of BCAAs helps to increase insulin sensitivity, which helps to treat and control diabetes (Cell Rep, 2016;16:520–530). Large amounts of BCAAs also caused liver damage in mice (EBioMedicine, Nov 2016;13:157–167).
Extra Protein Does Not Grow Muscles You need a certain amount of protein to build muscles, but taking more than that does not grow larger muscles. Taking large amounts of whey protein and BCAAs have not been shown to help enlarge muscles beyond just taking in an adequate amount of protein (J Int Soc Sports Nutr, 2017;14:30). The increased risk for heart attacks and diabetes seen in retired National Football League lineman may well be due to their massive intake of protein supplements and meat (The American Journal of Cardiology, May 1, 2008;101(9):1281-1284).
My Recommendations Resistance exercise, not protein loading, causes muscles to grow larger and stronger. The healthiest way for athletes (and everyone else) to meet their protein requirements is with unprocessed whole foods from the grocery store. Before you decide to follow a high-protein diet or take protein supplements, realize that your body cannot store excess protein. Any unused protein is burned for energy or stored as fat, and this process can stress your kidneys and liver. See How Much Protein Do You Need Extra Protein Does Not Enlarge Muscles
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