Despite our efforts spending hundreds of billions of dollars (likely trillions) researching and treating heart disease, it remains the #1 cause of death for women and men in the Western world.

For decades, scientists have blamed heart disease on red meat intake because it is loaded with cholesterol and saturated fat. The advice was a pillar of preventive medicine: ‘Limit red meat intake to avoid heart disease’.

But a problem has emerged with that cause-and-effect advice, as several studies now question whether consuming cholesterol or saturated fact necessarily impacts heart disease.

It turns out there may be something else about red meat that increases your risk for a heart attack or stroke, independent of cholesterol and saturated fat. The connection appears to be between red meat and your gut microbiome.

You’re probably familiar with the term “microbiome,” which refers to the friendly bacteria and other microbes that live in and on your body. We now know that the gut microbiome—ideally populated by a well-balanced mix of bacteria, fungi, and viruses—plays a major role in all aspects of health, including heart health.

Hippocrates, the father of modern medicine, wrote that “all disease starts in the gut.”

More than 2,000 years later, scientists made a discovery about a substance called trimethylamine N-oxide (TMAO), with findings that are right in line with his theory. Studies have shown that high blood levels of TMAO are associated with arterial plaque growth, clotting in the blood stream, and a dramatic risk in inflammation—itself a trigger for a host of illnesses and chronic disease.

One of many new studies on TMAO, published in the Journal of the American Heart Association, found up to a 62% heightened risk of a heart attack, stroke, or death in people with elevated TMAO, which is a far stronger relationship to heart disease than from either cholesterol or saturated fat.

So, you may be thinking, just avoid food with a lot of TMAO, right? Well, it’s not quite that simple, because food itself doesn’t contain TMAO. Instead, the gut microbiome makes TMAO from foods with nutrients like choline and L-carnitine,  nutrients that have health benefits, and that are abundant not just in meat, egg yolks and dairy products—the classic examples of high saturated fat/cholesterol—but also in foods regarded as heart-healthy, such as lean poultry, low-fat dairy, and fish. (Note: Although eating fish does raise TMAO levels, it is not associated with cardiac events, likely because of the anti-inflammatory properties of long chain omega-3 fats in seafood.)

Not only does eating red meat consumption increase the amount of L-carnitine available for TMAO production, it also appears to shift the balance in gut microbiome, fueling the growth of bad gut bacteria that produce TMAO. Yet, the TMAO production and growth of TMAO producing bacteria were reversed when the participants were crossed over to vegetarian diets (featuring vegetables, fruits, beans, nuts, and whole grains), or if they adopted a Mediterranean diet.

It turns out that a Mediterranean diet, (loaded with vegetables, fruits, beans, nuts, olive oil, balsamic vinegar, moderate red wine, and herbs and spices like garlic and Italian herbs, and generally avoids red meat)  will promote good gut bacteria and limit TMAO production, despite that the diet also contains moderate amounts of fish, poultry, yogurt, and cheese. The plant-based aspect of a Mediterranean diet creates a different gut microbiome that does not produce TMAO.

Part of the benefit of a Mediterranean diet is that it includes an abundance of probiotic rich foods, including plain yogurt, kefir, olives, capers, and pickled vegetables. If you are dairy intolerant and/or avoid dairy for other reasons, choosing other probiotic rich foods will help you support your gut microbiome as well.

I have also been researching how the gut microbiome impacts most of the major risk factors for heart disease: inflammation, obesity, cholesterol, diabetes, insulin resistance, and high blood pressure. If you maintain a healthy balance of microbes—nurturing the beneficial ones and eliminating those that do damage—you’ll enhance your control of these important risk factors, as well.

In later blogs, I will share how modifying your gut microbiome through diet can impact all these risk factors for heart disease, and how to boost your gut microbiome with the most beneficial microbes.

The good news is that there are many ways to benefit from following a Mediterranean diet, especially for your heart.

I wish you the best of health!

Steven Masley, MD, FAHA, FACN, CNS