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Eggs, Too, May Provoke Bacteria to Raise Heart Risk

By GINA KOLATA

For the second time in a matter of weeks, a group of researchers reported a link between the food people eat and bacteria in the intestines that can increase the risk of heart attacks.

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Two weeks ago, the investigators reported that carnitine, a compound found in red meat, can increase heart disease risk because of the actions of intestinal bacteria. This time they reported that the same thing happens with lecithin, which is abundant in egg yolks.

The lecithin study, published Wednesday in The New England Journal of Medicine, is part of a growing appreciation of the role the body’s bacteria play in health and disease. With heart disease, investigators have long focused on the role of diet and heart disease, but expanding the scrutiny to bacteria adds a new dimension. 

“Heart disease perhaps involves microbes in our gut,” said the study’s lead researcher, Dr. Stanley Hazen, chairman of the department of cellular and molecular medicine at the Cleveland Clinic Lerner Research Institute.

In the case of eggs, the chain of events starts when the body digests lecithin, breaking it into its constituent parts, including the chemical choline. Intestinal bacteria metabolize choline and release a substance that the liver converts to a chemical known as TMAO, for trimethylamine N-oxide. High levels of TMAO in the blood are linked to increased risk of heart attack and stroke.

To show the effect of eggs on TMAO, Dr. Hazen asked volunteers to eat two hard-boiled eggs. They ended up with more TMAO in their blood. But if they first took an antibiotic to wipe out intestinal bacteria, eggs did not have that effect.

To see the effects of TMAO on cardiovascular risk, the investigators studied 4,000 people who had been seen at the Cleveland Clinic. The more TMAO in their blood, the more likely they were to have a heart attack or stroke in the ensuing three years.

Carnitine — the red meat chemical — and lecithin are chemically related, Dr. Hazen said. As with lecithin, when carnitine is digested, choline is released and can be acted on by intestinal bacteria. 

The results of the new studies, though, do not directly prove that reducing TMAO protects against heart disease. That would require large studies following people who lowered their TMAO levels, which should be possible with a vegetarian or high-fiber diet.

Dr. Hazen said that people who are worried about heart attacks may want to consider reducing lecithin and choline in their diet, which would require eating less of foods high in fat and cholesterol. Dr. Hazen said it also may be wise to avoid supplements or vitamins with added choline.

In an accompanying editorial, Dr. Joseph Loscalzo of Brigham and Women’s Hospital in Boston suggested that in the future there may be other ways to reduce blood levels of TMAO. People might take probiotics to help grow bacteria that do not lead to an increase in TMAO. Or perhaps drugs could squelch the synthesis of TMAO. Those probiotics and drugs, though, do not yet exist, and even the specific bacteria responsible for the increase in TMAO are not yet identified.