Athletes in sports requiring great strength who eat a very-high protein diet increase their risk for dying at a young age of heart attacks, even though protein loading does not grow larger muscles.
A recent study by Stanley Hazen at the Cleveland Clinic has identified a chemical produced by human colon bacteria called phenylacetylglutamine (PAG) that causes clots that can cause heart attacks (Cell, March 5, 2020). This could explain why young body builders and weightlifters have such a high rate of heart attacks, even though the recent literature shows that strength training and having large muscles helps to prevent heart attacks (Med & Sci in Sports & Ex, March 2019;51(3):499-508). There is no question that the anabolic steroids that many weightlifters take to help them grow larger muscles markedly increase risk for forming plaques in arteries and the chances of dying from heart attacks (Circulation, 2017;135:1991–2002). However, those who eat the most meat are also at high risk for heart attacks (Arch Intern Med, 2012;172(7):555-563), and eating lots of red meat increases risk for type 2 diabetes (Am J Clin Nutr, 2011;94(4):1088-1096) and cancer (Nutr Cancer, 2009;61(4):437-446). Furthermore, taking in large amounts of whey protein from milk has been associated with increased heart attack risk (American J Emerg Med, 2017;35:664).
How Can Protein Loading Cause Heart Attacks?
Human protein is made up of 21 building blocks called amino acids. When you eat dietary sources of protein, your intestinal enzymes separate the protein into amino acids and you absorb singles and chains of amino acids into your bloodstream. However, when you overload on protein from plants or animals, some of the amino acids are not absorbed in the upper intestines and pass to your colon. In particular, one unabsorbed amino acid, phenylalanine, is then broken down by colon bacteria to form phenylacetic acid, which passes to the liver, where it is converted to phenylacetylglutamine (PAG). PAG causes clots to form anywhere in your body to cause heart attacks, strokes and lung clots. Since absorption of large amounts of phenylalanine occur in the colon only when you overload on protein, this explains why eating too much protein can cause heart attacks.
The researchers also demonstrated that PAG causes clots through the sympathetic nervous system that produces adrenalin. Taking drugs called beta blockers that block adrenalin from the sympathetic nervous system helps to prevent clotting and heart attacks.
This is a potential Nobel Prize for Dr. Stanley Hazen, if further research by other investigators supports his brilliant discovery that protein loading from meat or plants increases production by colon bacteria of a chemical called PAG that is known to cause clots that cause most heart attacks and strokes.
Scientists have known for many years that people who eat large amounts of meat are at increased risk for dying prematurely from heart attacks, diabetes and certain cancers, but they have blamed the fat, saturated fat and cholesterol, which are all components of high-protein foods. Dr. Hazen’s research suggests that the protein itself may be the culprit. While we await further studies, I recommend avoiding the very high protein diets. You do not need a lot of extra protein to build muscle.