A recent study published in the prestigious scientific journal Nature Medicine has sent waves through the natural health community by linking L-carnitine, a nutrient in red meat, with heart disease.1 L-carnitine has recently been approved for public use by Health Canada and has a large body of research supporting its health benefits. There is research supporting its use in heart disease, chronic fatigue syndrome, infertility, erectile dysfunction, chronic obstructive pulmonary disease (COPD) and diabetes. Some of the more specific cardiovascular benefits include increased survival after heart failure, increased exercise tolerance in patients with chronic angina, decreased total cholesterol and increased HDL cholesterol levels in patients with hypertension, and improvement in muscle recovery after exercise.2-5 How can such a well-studied nutrient suddenly contribute to the very condition that many integrative doctors and patients use it to prevent and even treat?
As with all new research, a closer look is required at the conclusions and methods used in the study. Just a brief scan of the abstract and title shows that the intent of the study was not to highlight the negative effects of carnitine. The intent of the study was to show the significance of gut bacteria on the metabolism of carnitine and its possible link to cardiovascular disease.
“Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis.”
The study reported that specific strains of bacteria in mice converted L-carnitine to trimethylamine-N-oxide (TMAO), a compound linked to the formation of atherosclerosis. Furthermore, mice that were pretreated with antibiotics (which killed the gut bacteria) did not produce TMAO, suggesting that the specific strains of bacteria in the gut were the problem. The only human evidence portion of the study reported that people with higher plasma L-carnitine levels have increased risks for cardiovascular disease.
It is easy to scan the title and summary of the study and conclude that L-carnitine increased the chance of heart disease, however this is not what the results show. There is no doubt that vegetarians have a lower rate of heart disease, but this study does not prove that L-carnitine from meat causes the problem. It simply shows that your intestinal bacteria can have an effect on the metabolism of nutrients and they can possibly alter the effects of these nutrients in the body. This is not a new concept. Emerging research has linked probiotics and gut flora to seemly unrelated conditions such as obesity, depression, allergies and inflammation. Interestingly, a recent study showed an increase in TMAO levels, foam cell formation and aortic atherosclerosis in mice that were fed phosphatidyl choline (PC), a nutrient commonly used to address cardiovascular conditions. Again, these observations were dependent upon specific gut flora.6
Another important point to remember is that the bacteria found in the digestive system of mice varies greatly from that in humans; therefore it is premature to extrapolate the results. We should also consider that a diet high in red meat (which also happens to be high in carnitine) may have other negative effects on heart disease independent of carnitine. The human portion of the study showed that people with higher plasma L-carnitine levels predicted increased risks for cardiovascular disease; however this does not prove cause and effect. There are many things (saturated fat, environmental toxins etc.) found in red meat that can have a negative effect on cardiovascular health. L-carnitine may just be acting as a “biomarker” of red meat consumption rather than the culprit.
When considering new and emerging research, it is always prudent to proceed slowly and carefully before drawing broad conclusions. This study highlights this point and it is unfortunate that media outlets like the New York Times have splashed misleading headlines all over North America.7 Although this study does not show any definitive link between L-carnitine use and heart disease, it does demonstrate a link between our gut bacteria and the formation of potentially harmful compounds that may be linked to diseases. It also highlights that we need to continue to study nutrients like L-carnitine to fully understand how it is used and metabolized in the body. Based on the conclusions of this study, we can say that a person with existing heart disease should consider a move towards a more vegetarian or plant based diet (not just to avoid carnitine) and explore ways to promote a healthy gut flora.
You may also be interested in: “L-Carnitine, Red Meat & Gut Bacteria”
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