06/10/2013 10:35 am ET Updated Aug 10, 2013

You Are What You Eat: Gut Bacteria and Heart Disease

They say "the way to a man's heart is through his stomach," and the connection between diet and heart disease is nothing new. It has been generally accepted that the saturated fat in meat makes it a cardiac killer.

Well, this just in, fat may not be the culprit in the red meat-heart disease equation. Recent evidence suggests that the troublemaker is L-carnitine, an amino acid (protein building block) found in meat and a commonly used health supplement.

Over the past decade, research has demonstrated how our diet defines the bacteria that live in our gut. And who lives in our gut turns out to be very important. For instance, diets high in processed foods promote gut bacteria that are associated with inflammation, obesity and Type 2 diabetes. New findings suggest that meat eaters' gut bacteria process L-carnitine producing the compound, trimethyamineoxide (TMAO). TMAO is significantly correlated with cardiovascular disease.

In one of several elegant experiments, the investigators administered antibiotics to eliminate the gut bacteria prior to giving test subjects dietary L-carnitine. No TMAO was produced. This confirmed the essential role of the gut bacteria in producing TMAO and linked it to heart disease.

A growing appreciation of the profound role gut bacteria play in health puts a new spin on the adage "you are what you eat." By eating certain foods, we determine which bacteria will inhabit us. These bacterial populations that colonize our gut far outnumber our own cells. They not only determine how we harvest dietary nutrients but modulate key pathways such as fat metabolism and inflammation. In this way, the flora in our gut are linked to our most common diseases: obesity, Type 2 diabetes and heart disease.

Gastric bypass has proven a very effective (and tremendously invasive and expensive) intervention for severe obesity and Type 2 diabetes. Until recently it was thought that the procedure was therapeutic because it caused a mechanical restriction of the gut and impaired calorie absorption. We now know that the operation alters the basic physiology of energy balance and metabolism in large part by changing the gut bacteria. In an extraordinary series of experiments, Lee Kaplan at Harvard University and Peter Turnbaugh at Massachusetts General Hospital demonstrated that transplanting bacteria had the same effect as the surgery.

In the not too distant future, analyzing our gut bacteria will be common practice. Fecal transplants are already part of the medical armamentarium. In the same way that we have realized the need to protect natural balances in the external environment, we must do the same with our internal biosphere. Let the personal environmentalism movement begin.

For more by Paul Spector, M.D., click here.

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