It’s no secret that going hard on the steaks and burgers isn’t going to do your heart any good. This effect is typically put down to the high amounts of fats and cholesterol found in red meats, but a new study suggests another culprit might be responsible: bacteria in your gut.

As reported in the journal Nature Microbiology, a new study builds on evidence that gut bacteria and a compound produced by some of them – trimethylamine-N-oxide (TMAO) – have an intriguing link to the increased risk of heart attacks and strokes seen in people with a diet heavy in red meat.

Our intestines are home to trillions and trillions of microorganisms. Most are perfectly harmless and, in fact, play a diverse range of important functions such as breaking down food, manufacturing vitamins, guiding metabolism, and bolstering our immune system. Some of this work is carried out through the compounds the bacteria produce and secrete. One of these compounds is TMAO, which is produced by certain bacteria from choline, lecithin, and carnitine, three nutrients that are in many animal products but are especially abundant in red meat and liver. 

In this latest study, a team of researchers from the Cleveland Clinic found that high levels of circulating TMAO in the body have been shown to be a strong indicator that a person is at risk of heart attacks, stroke, and even death. Furthermore, they discovered a two- to three-fold increase in TMAO levels in people who ate red meat as their primary source of protein for one month, compared to participants who relied on white meat or plant-based foods as their prime protein source.

There is some good news, however: some of the impacts of red meat on gut bacteria and TMAO appear to be relatively reversible. Their research indicated that TMAO levels dropped to healthier levels within three to four weeks after cutting red meat from their diet. 

“We know lifestyle factors are critical for cardiovascular health, and these findings build upon our previous research on TMAO’s link with heart disease,” Dr Stanley Hazen, study author and Chairman of the Department of Cellular and Molecular Medicine at Cleveland Clinic’s Lerner Research Institute, said in a statement. “They provide further evidence for how dietary interventions may be an effective treatment strategy to reduce TMAO levels and lower subsequent risk of heart disease.”

Through working with isolated bacteria, the team investigated how microorganisms in the gut create TMAO from choline, carnitine, and lecithin. This knowledge, they believe, could help pave the way towards medical and nutritional interventions that reduce a person’s risk for cardiovascular disease.

“We can use a TMAO level to help personalize dietary choices in an individual to help identify, for a given person, how much red meat is too much, and how to try to chase after lowering the level, much in the same way we do with cholesterol levels or triglyceride levels or glucose levels,” Dr Hazen explains.