A Bacteria Hidden In Our Guts Might Be Causing All Our Heart Disease

You know all about cholesterol and fat, but have you heard of TMAO? Probably not. But a bacteria that lives in our guts excretes it when we eat meat, and now scientists think it might be the cause of our heart problems.

A Bacteria Hidden In Our Guts Might Be Causing All Our Heart Disease
Kelly Rakowski/Co.Exist

Whether it was because my mom refused to take me to McDonald’s as much as I wanted or because I’d never seen my dad eat a piece of bacon or steak, one of the first nutrition lessons I learned as a child was, more or less: “Red meat is bad, so you can’t eat too much of it.” When I got a bit older, I began to understand the explanation: Saturated fat and cholesterol clogged the arteries and caused a heart attack.


But now, scientists at the nonprofit medical research center the Cleveland Clinic are revisiting that basic cause and effect about what makes red meat pernicious. And their results, which others in the scientific community say are promising, show that maybe there’s a whole other explanation for why red meat puts steak lovers’ hearts at risk. As the New York Times reports:

[R]esearchers had come to believe that what damaged hearts was not just the thick edge of fat on steaks, or the delectable marbling of their tender interiors. In fact, these scientists suspected that saturated fat and cholesterol made only a minor contribution to the increased amount of heart disease seen in red-meat eaters. The real culprit, they proposed, was a little-studied chemical that is burped out by bacteria in the intestines after people eat red meat. It is quickly converted by the liver into yet another little-studied chemical called TMAO that gets into the blood and increases the risk of heart disease.

Carnitine is the name of the chemical that becomes TMAO. It’s found mostly in red meat, but in other proteins too, and increasingly (and perhaps, disturbingly) in energy drinks “on the assumption that is will speed fat metabolism and increase a person’s energy level.”

But of the two chemicals, it seems that TMAO–which spikes in a meat eater’s blood level after polishing off a burger–is the more dangerous one. According to the Times.

TMAO levels turned out to predict heart attack risk in humans, the researchers found. The researchers also found that TMAO actually caused heart disease in mice. […]

“It’s really a beautiful combination of mouse studies and human studies to tell a story I find quite plausible,” said Dr. Daniel J. Rader, a heart disease researcher at the University of Pennsylvania School of Medicine, who was not involved in the research.

The researchers hypothesize that TMAO lets cholesterol enter artery walls and keeps the body from “excreting excess cholesterol.”

And while the work eventually may help come up with new ways to prevent heart disease, like antibiotics to kill the bacteria that excrete TMAO, for now, it’s just raising a lot of questions: Is TMAO what’s causing heart disease? Which bacteria in the stomach turn carnitine to TMAO? Is it dangerous to put carnitine in energy drinks? And–perhaps most important to advocates of the latest fad diet–should people stop doing the meat-intensive Paleo diet?

The research was published in the journal Nature Medicine over the weekend.


[IMAGE: Steak via Shutterstock]

About the author

Zak Stone is a Los Angeles-based writer and a contributing editor of Playboy Digital. His writing has appeared in,, Los Angeles, The Utne Reader, GOOD, and elsewhere.