Steak-Loving Gut Microbes Linked To Heart Disease

New research has discovered a link between cardiovascular disease and the nutrient l-carnitine found in red meat — meaning even unfried, low-fat meats could cause your artery walls to thicken. The good news is that l-carnitine can only damage the heart after being converted into compounds by intestinal bacteria. The bad news is that these bacteria are probably already in your belly.

Researchers from the Cleveland Clinic Foundation in the US studied the disease-promoting effects of l-carnitine in mice. They discovered that the aforementioned nutrient increases the risk of cardiovascular disease following metabolisation by stomach microbes into the compound trimethylamine N-oxide (TMAO). TMAO is capable of damaging arteries supplying blood to the heart and brain.

Our results suggest a previously unknown mechanism for the observed relationship between dietary red meat ingestion and accelerated atherosclerosis [the cause of heart attacks, strokes and vascular diseases]. Consuming foods rich in l-carnitine (predominantly red meat) can increase fasting human l-carnitine concentrations in the plasma3. The role of gut microbiota in this pathway suggests new potential therapeutic targets for preventing CVD.

As the report notes, l-carnitine is also a common ingredient in over-the-counter dietary supplements, so pill-popping vegos aren’t completely in the clear. However, because vegans and vegetarians don’t regularly partake in red meat, the population of compound-producing bacteria in their bellies was found to be much smaller.

The present studies suggest that the reduced inges¬tion of l-carnitine and total choline by vegans and vegetarians, with attendant reductions in TMAO levels, may contribute to their observed cardiovascular health benefits. Conversely, an increased capacity for microbiota-dependent production of TMAO from l-carnitine may contribute to atherosclerosis, particularly in omni¬vores who consume high amounts of l-carnitine.

Australian scientists respond

So what does this mean for meat eaters? Do we all need to start wearing tie-dyed shirts and Third World trinkets while preaching about the holistic benefits of a vegan diet? Australian scientists are currently divided on the matter.

According to Professor Mark Wahlqvist, Emeritus Professor of Medicine at Monash University, the reports methods and findings are pretty sound:

We are used to rather simple assumptions about how dietary components affect health. That has been changing and increasingly it is clear that it is more reliable to consider food patterns and health outcomes and that an emphasis on variety and plant foods is the over-riding guideline for healthy eating.
The new study published supports this, in that it finds yet another factor in meat which may increase the risk of heart disease and stroke, namely l-carnitine, which is important in fat metabolism. It is increasingly evident that carnitine may not be safe as a nutrient supplement and that the safest way to obtain it from the diet is from a varied plant-based diet.

Shawn Somerset, Associate Professor of Public Health at the Australian Catholic University was similarly satisfied by the findings:

These results add further support to previous substantial research showing that excessive meat consumption is associated with increased risk of a range of chronic diseases. Meat is an excellent dietary source of iron and a range of other minerals and there are some Australians with insufficient intakes of these nutrients. The public health challenge continues to centre around developing strategies to prevent deficiencies in these nutrients whilst avoiding the adverse consequences of excessive meat consumption.

However, Professor Garry Jennings from the Heart and Diabetes Institute was somewhat less impressed:

This evidence is not sufficiently compelling to cause concern amongst the red meat industry and a balanced diet remains the best recommendation for Australians. While the paper makes some clever observations, the overall evidence that red meat is harmful is not consistent with a broader body of evidence. Carnitine is needed by the body to help oxidise fat. It is provided both in the diet from meat and dairy food, and is made by the body from lysine and vitamin B6…
There is very little evidence to support its efficacy.

Professor Peter Clifton, Professor of Nutrition at the Samson Institute at the University of South Australia also has some reservations:

It is a very interesting hypothesis but unprocessed red meat has not been found in meta-analyses to be associated with cardiovascular disease, while of course vegetarian sources of choline would also be a problem for the formation of TMAO (eg quinoa, soymilk, and broccoli).

All the scientists who released statements agreed that more research was needed. Regardless of the outcome, we’ll continue to treat our squirmy, microscopic pals to regular servings of hot, juicy steak. Better dead than vegan, I say.