Red meat and heart disease
Many studies in the last few decades have shown that there is a link between red meat consumption and heart disease. The old-fashioned (and incorrect) thinking was that the saturated fat and cholesterol in the meat were the culprits. One study suggests some alternative culprits.
Dozens of scientific studies referred to in Grow Youthful show that the saturated fat and cholesterol in our food are beneficial rather than harmful. Indeed, they are essential for good health.
The study (1) may explain the link between saturated fat and heart disease. Stanley Hazen suggests that the blame lies within the microbiome - the ecology of 100 trillion bacteria that live in the human gut. These bacteria play an essential role in health and life. They produce a variety of vitamins and other micronutrients; fend off infections by harmful microorganisms; digest complex carbohydrates that human enzymes cannot handle; and play many other beneficial roles.
In earlier studies in 2011 Dr Hazen demonstrated that some gut bacteria can convert choline (a molecule found in eggs and meat) into trimethylamine, which is then processed in the liver to create trimethylamine N-oxide or TMAO. TMAO interferes with liver enzymes that make bile acids. Bile is necessary for effective and efficient digestion, the removal of excess cholesterol (and many other functions). TMAO also disrupts cholesterol metabolism in other parts of the body, including artery walls. Basically, TMAO causes atherosclerosis.
Now, his 2013 study (1) shows that some bacteria can also convert carnitine into TMAO. Carnitine is somewhat similar to choline, and is also abundant in red meat.
The problem only seems to occur when certain gut bacteria are out of balance. Hazen noted that omnivorous people (those who regularly eat meat) produced more TMAO than did vegans or vegetarians who ate some meat just for this study after previously avoiding it.
In one test five human volunteers ate 225 gm / 8 oz sirloin steaks plus a carnitine supplement. This diet produced high levels of both carnitine and TMAO in the volunteers' blood. But after the same people were given antibiotics to kill their gut microbes, the same steak meal produced little TMAO, even though their carnitine levels went even higher than before. This showed that the production of TMAO needs certain bacteria.
These bacteria are not always present. Dr Hazen persuaded a vegan volunteer to eat a steak. The vegan's subsequent TMAO level did not rise. This suggests that the vegan's particular gut bacteria did not contain species that convert the carnitine. Some vegetarian volunteers, given carnitine pills but spared the steak, showed similar results.
Dr Hazen looked at the association between heart disease and levels of carnitine and TMAO in more than 2,500 people. He found there was indeed an association between heart disease and carnitine, but only when TMAO levels were high. At this stage Dr Hazen does not know if taking carnitine supplements can cause TMAO, or how TMAO wreaks its havoc on arteries.
An analysis of the faeces of both vegetarians and meat eaters led Dr Hazen to suspect bacteria of several genera, including Clostridium and Fusibacterium.
- Do not regularly eat large quantities of red meat. A variety of problems are caused not by eating meat, but by eating too much meat. A small quantity that can easily fit into the palm of your hand is the most you need in a day.
- Bacterial imbalance, particularly that caused by antibiotics, is damaging to health and life. Traditional probiotic fermented foods help restore and maintain the balance in the gut biome.
1. Robert A Koeth, Zeneng Wang, Bruce S Levison, Jennifer A Buffa, Elin Org, Brendan T Sheehy, Earl B Britt, Xiaoming Fu, Yuping Wu, Lin Li, Jonathan D Smith, Joseph A DiDonato, Jun Chen, Hongzhe Li, Gary D Wu, James D Lewis, Manya Warrier, J Mark Brown, Ronald M Krauss, W H Wilson Tang, Frederic D Bushman, Aldons J Lusis, Stanley L Hazen.
Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis.
Nature Medicine (2013) doi:10.1038/nm.3145. Published online 07 April 2013.