New Heart-Health Threat: Compounds in Red Meat, Egg Yolks and More

Reviewed by Stanley Hazen, MD, PhD, Department Chair of Cellular and Molecular Medicine and Section Head of Preventive Cardiology and Rehabilitation at the Cleveland Clinic.

A growing stack of research suggests that compounds in red meat, egg yolks and high-fat dairy products raise risk for heart disease—a leading health threat for people with diabetes—via a surprising route: Gut bacteria that help convert choline and carnitine from these foods into a chemical that crams heart-menacing plaque into artery walls.

egg yolks and beefOne recent study suggests there may be even more fall-out for people with high levels of trimethylamine N-oxide, or TMAO. Australian researchers reported in a July 2015 review in the journal Metabolism that TMAO may be one reason type 2 diabetes risk rises for people who eat a lot of red meat.

TMAO harms heart health by encouraging the deposit of more cholesterol in artery walls. It also interferes with the process that whisks LDL cholesterol out of the body in bile acids. And it may also increase inflammation.

In late December, the Cleveland Clinic researchers announced they’d found a potential antidote. A chemical called DMB stops gut bacteria from converting choline and L-carnitine into TMA (trimethylamine— the compound that the liver turns into nasty TMAO). In lab studies, DMB kept TMAO levels in the blood lower and led to a shrinking of artery plaque. And in the intestines, levels of TMA-producing bacteria dropped. The study was published in the December 17, 2015 issue of the journal Cell.  

DMB is found in some types of extra-virgin olive oil, grapeseed oil, balsamic vinegar and red wine, according to the study.

Lead researcher Stanley Hazen, MD, PhD, Department Chair of Cellular and Molecular Medicine and Section Head of Preventive Cardiology and Rehabilitation at the Cleveland Clinic says it’s too soon to for a specific TMAO-clobbering dietary prescription for people. In part, that’s because individual differences in gut bacteria make a big difference in TMAO levels. “It's more about the gut microbes than the diet, though chronic dietary efforts can change the gut microbe composition and lower TMAO” “Even so, many vegetarians have high TMAO,” he says. That is why Dr. Hazen suggests a that a person with a high blood TMAO level should consider more aggressive preventive efforts – such as keeping blood pressure, cholesterol and weight down to healthy levels. 

In fact, Dr. Hazen and his team hope that someday soon, their work will lead to a TMAO treatment that targets gut bacteria. (An enthusiastic editorial published with the study was titled “Drug the Bug!”) Still, his research has turned up food clues that could help and can’t hurt:

  • Carnitine and choline in red meat and egg yolks raise TMAO levels. In two human studies, Dr. Hazen’s team found that TMAO levels increased after people ate two hard-boiled eggs or an 8-ounce sirloin steak. L-carnitine is also found in some dietary supplements and energy drinks. Choline (which comes from dietary phosphatidylcholine or lecithin) is found in animal products, egg yolks, high fat dairy products and in many processed foods.

    In a 2013 study of 4,007 people, Dr. Hazen found that heart-attack and stroke risk was 2 ½ times higher in those with high TMAO levels compared to those with the lowest levels. “I strongly encourage the Mediterranean diet because it has the best outcome data reported,” Dr. Hazen says. In one recent study, he notes, people who consumed a Mediterranean diet and specifically avoided red meat showed a 30% reduction in cardiovascular events over almost 5 years. Other research shows that people who stick more closely to Mediterranean-style eating have lower TMAO levels, Dr. Hazen notes.   
  • There’s DMB is some extra-virgin olive oils as well as some grapeseed oil, red wine and balsamic vinegar. “DMB was found in highest levels in some cold pressed extra-virgin olive oil,” Hazen says. “It was never found in cheaper extra virgin olive oil blends. The boiling point of DMB is very low, just above the boiling point of water. So cooking with olive oil would it evaporate away—just like cooking with wine does to ethanol.”   

People with diabetes may want to pay special attention to future news about TMAO, says Peter Clifton, PhD, Professor of Nutrition at the University of South Australia and lead author of the review on red meat and diabetes. “It should pose more risk for people with diabetes and low HDLs,” he said in an email interview.

More human studies are needed, Dr. Clifton adds. Some studies and reviews, for instance, suggest carnitine could play protective roles in the body and in cardiovascular disease. In the meantime, he says, “I think meat minimization and processed meat [ham, bacon, sausage] avoidance is good advice for all.”

Updated on: February 1, 2016
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