Party on, vegans

fish and fish — in other words, animal products.

Since the researchers had no idea what compounds they were looking for, they actually had to do some research of their own on TMAO, and soon found studies demonstrating that choline, which is converted to TMAO in the digestive tract, accelerated atherosclerosis (hardening of the arteries) in animals.

Next, Hazen’s group looked at the relationship between TMAO and heart health in a large human population, and sure enough, they found a very clear association with high circulating levels of TMAO and heart disease risk. But that still doesn’t prove cause and effect. So, to come one step closer, they gave a group of subjects two eggs — one of the richest sources of lecithin, the nutrient that breaks down into choline, which is then fermented to TMAO — and sure enough, TMAO levels climbed shortly after.

Finally, to confirm the relationship between the intestinal bacteria and TMAO, they gave the subjects antibiotics to wipe out the bacteria in their digestive system, and TMAO levels crashed.

In a separate set of experiments, the research team also examined the effect of carnitine, a prominent compound in animal foods that is chemically related to lecithin, on TMAO and heart disease risk. After feeding subjects a carnitinerich food — steak — they saw a similar spike in TMAO levels as they had with eggs. They also found that TMAO encourages more cholesterol to be deposited into the arteries, while simultaneously reducing the body’s ability to eliminate it. As with the studies on choline, the research team also measured the capacity of carnitine levels in the blood to predict heart disease in a pool of more than 2,500 subjects, and found that, as Hazen put it, “carnitine is as good or better as anything we are currently using to measure for atherosclerosis. But really, when we isolated for just TMAO, it was the real culprit.”

If these findings leave you feeling bewildered, you’re not alone. After all, eggs have largely been on the nutritional upswing lately, and carnitine is popular in sports supplements and energy drinks. So now we are to believe that they are triggering heart attacks? They might, but remember that this research is still very new.

There may, for example, be other factors that can help us to control TMAO levels, much like oat bran helps to reduce cholesterol, that simply haven’t been discovered yet. In the meantime, it makes sense to follow existing recommendations to emphasize plant foods in our diet, while keeping meat and other animal foods, which tend to be rich in both carnitine and lecithin, moderate (remember that your body cannot use any more than about 30 grams of protein, equal to a serving of meat about the size of the palm of your hand, to build muscle after any one meal, so a 16-ounce Porterhouse is going overboard by any measure). It also suggests that supplements or food products with added lecithin or carnitine would be best left on the shelf, at least until we know more.