 As I've explored before, whether you're young or old, male or female, smoker or non, high blood pressure, low blood pressure, high cholesterol, or low, having high levels of a toxic compound called TMAO, trimethylamine oxide, in your bloodstream, is associated with a significantly higher risk of having a heart attack, stroke, or dying over a three-year period. Where does TMAO come from? The choline in foods like eggs can be turned by gut bacteria into TMAO, which is then absorbed back into our system, and the more eggs we eat, the higher the levels climb. Given the similarity in structure between carnitine and choline, the same group of Cleveland Clinic researchers wondered if carnitine, found in red meat, energy drinks, and supplements, might also lead to TMAO production, so they put it to the test. If you feed someone a steak, their TMAO levels shoot up. Now this was someone who regularly ate meat. Those who eat strictly plant-based may start out with almost no TMAO in their system, presumably because they're not eating any meat, eggs, or dairy, but even if the vegan eats a sirloin, almost no TMAO is made. Why? Presumably they don't have steak-eating bacteria in their guts. No TMAO is produced if you don't have TMAO-producing bacteria in your gut. If you don't regularly eat meat, then you're not fostering the growth of the meat-eating microbes that produce TMAO. This suggests that once we develop a plant-based gut ecosystem, our bacteria will not produce TMAO even if we eat meat every once in a while. However, we still don't know how rapidly gut bacteria shifts after a shift in our diet, but it does not appear to be all or nothing. If you take men eating a standard American diet and have them eat two sausage, egg, and cheese biscuits before and after just five days of eating lots of high-fat meals like that, you can boost TMAO production even higher. So it's not just do you have the bad bugs or not, you can apparently breed more of them the more you feed them. On the other hand, meat-free diets have been demonstrated to have a profound influence on human metabolism. You can analyze a urine sample and tell what kind of diet people eat based on measurements like how low their TMAO levels are in the urine of those eating egg-free vegetarian diets. You can even take the same people and rotate them through three different diets, and you can tell who is who who's on a high-meat, low-meat, or no-meat diet, in part based on the different compounds churned out by the different gut flora or different flora activity after just about two weeks on the different diets. It's possible that some of the beneficial effects of whole plant foods may be mediated by the effects they have on our gut bacteria. At the same time, the standard American diet may increase the relative abundance of undesirables that produce toxic compounds, including the cardiotoxicant TMAO. Strictly plant-based diets have gained acceptance as a dietary strategy for preventing and managing disease, perhaps in part because of their rather unique gut flora, less of the disease-causing bacteria and more of the protective species. So all along we thought the reason those eating plant-based had lower heart disease rates was because they were eating less saturated fat and cholesterol, but maybe their lower TMAO levels may also be contributing to their benefits thanks to the reduction of ingestion of carnitine and choline. I talked about the egg industry response to the choline revelation. How has the carnitine supplement industry reacted? Well, the former VP of Advocare, a multilevel marketing company that sells carnitine supplements like SLAM, while getting SLAM'd with lawsuits, finding them, for example, guilty of false misleading or deceptive practices, forced to pay over a million dollars, in response to the research implicating carnitine in TMAO production, he questioned whether there was a secret vegan conspiracy at the Cleveland Clinic, and that restricting our intake of meat or carnitine supplements to prevent our gut bacteria from making TMAO, he argues, is like trying to prevent car accidents by restricting the sale of fuel. Ah, okay, but there are benefits to transportation. We're talking about TMAO, which may be fueling our epidemic of heart disease, the number one killer of men and women in this country. As far as I'm concerned, the more we can cut the fuel for that, the better.