More on TMAO and heart attacks
More on TMAO and Heart Attacks

For the last two weeks I have reported on the growing interest in TMAO 
as a cause of heart attacks. In the latest study, Dr. Stanley Hazen at 
the Cleveland Clinic measured fasting blood TMAO levels in 4,007 
patients who received coronary angiography to see if the blood vessels 
to their hearts were blocked. Three years later, those with the highest 
levels of TMAO had more than twice the risk of having a heart attack 
than those with the lowest levels (N Engl J Med, April 25, 2013; 

The researchers fed lecithin to healthy human volunteers and blood 
levels of TMAO shot up. They gave volunteers antibiotics and blood 
levels of TMAO barely rose at all. This showed that bacteria in the 
intestines converted lecithin to TMAO. Eggs, liver, beef, and pork are 
the principal sources of carnitine, choline, lecithin and creatinine, 
the substances which can be converted by bacteria in the intestines to 

TMAO has been shown to punch holes in the inner linings of arteries of 
mice. When these holes start to heal, TMAO helps cholesterol attach to 
the damaged inner linings to form plaques. TMAO also raises cholesterol 
by making it more difficult for the liver and the intestines to clear 
cholesterol from the body.

Since Ancel Keys' groundbreaking studies in the 1940s, we have known 
that eating meat is associated with increased risk for heart attacks. 
Keys thought that the increased risk was caused by the saturated fats 
in meat, eggs and high-fat dairy products. However, large population 
studies have failed to show that saturated fats from plants (coconut, 
palm and palm kernal oils) increase risk for heart attacks. Therefore, 
many doctors no longer accept the theory that saturated fat in meat is 
the main cause of heart attacks. Other possible explanations for the 
association include:
 Inflammation (an overactive immunity) against Neu5Gc, a chemical in 
mammal meat and dairy products,
 Inflammation caused by infections or auto-immune diseases,
 Excess iron from meat,
 Nitrates from meat, particularly processed meats.
However, none of these theories has been widely accepted. The recent 
studies on TMAO offer the most promising explanation for the 
association between eating red meat and suffering a heart attack.