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L-Carnitine Linked to Clogged Arteries?

There is lots of research to support L-carnitine's benefits to cardiovascular health. So when I usually see headlines regarding L-carnitine and cardiovascular health and risk, L-carnitine usually has a protective role. That's why it was surprising when I came across this study that suggests the opposite: that L-carnitine increases the risk of cardiovascular disease.

For many of you using L-carnitine for cardiovascular health, cognitive health (acetyl-L-carnitine), and even weight loss, don't be alarmed. This study is just an anomaly is a sea of positive studies. However, it does deserve some discussion, so let's break it down.

In this newly published study, researchers examined carnitine levels in 2,595 heart patients, and found high levels were associated with increased risk of heart disease, heart attack and stroke – but only when TMAO (trimethylamine-N-oxide) levels were also high. TMAO is a substance that has been linked to cardiovascular disease, and it's been shown that specific bacteria in the intestines biotransform (metabolize) L-carnitine into TMAO. Further, their population growth can be promoted by diets high in carnitine.

Since dietary carnitine is found only in meat, TMAO levels in vegetarian and vegan participants were significantly lower than in omnivores (since their diet does not promote the growth of the specific bacteria, so when they do ingest carnitine, they do not produce significant levels of TMAO).

However, there will always be positive and negative studies surrounding any therapy. The trick is not to look at the study of the day, but consider the totality of evidence, and for carnitine, the vast bulk of studies show amazing health benefits to many health conditions, including cardiovascular health.

Update: following this post, I covered 4 positive studies on L-carnitine...

In this situation, whole meat and even L-carnitine supplements are probably not the main issue here. Healthy diets can be rich in 'red' free-range, grass-fed, and ideally organic meat (in addition to fruits, vegetables, healthy fats, etc.) and still improve the gut flora and health risk factors. The systematic review that the researchers cite themselves concludes that "consumption of processed meats, but not red meats, is associated with higher incidence of [coronary heart disease] and diabetes mellitus."

Furthermore, L-carnitine has been shown the potential to prevent clogged arteries in other studies, and the mouse model used in the present study (an abnormal genetically-modified species) may not be the best transferable model to humans, and therefore, the results may not be relevant to humans (just like studies on soy phytoestrogens showed negative effects for breast cancer in animal studies, while human studies showed benefits to breast cancer patients). There are many uncertainties around this study, so don't get tied-up in a knot over these results.

Source:Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis

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  1. Great breakdown of this research on l-carnitine - very interesting to learn about bacteria and diet modifying it's metabolism.
    Thanks for the great reviews!

    1. This is extremely interesting stuff, and likely you'll hear of MANY more studies on bacterial biotransformation.

      I'll give you a story about my first experience in understanding this. Back in 2007/08, I worked for company who wanted to develop their own proprietary ingredient. Being based out of Ontario, Canada--and Ontario being the largest exporter of ginseng in the world, specifically Panax quinquefolius--we wanted to use this botanical. My job was to find out what we wanted from this plant.

      You've likely heard of the ginsenosides, a group of compounds in ginseng that is thought to be responsible for much of ginseng's health benefits. Well, as it turns out, most of it is NOT absorbed as ginsenosides. The bacteria in the intestines metabolize these ginsenosides to other compounds, which ARE therapeutic, and that's what we absorb. Interestingly, specific bacterial species metabolized specific ginsenosides.

      So this is probably the reason why there is so much therapeutic variability between people using ginseng (and essentially any botanical medicine, or even just food). If someone doesn't have a good amount of very specific bacteria, they will not biotransform what they ingest and may not get the same therapeutic results as someone who does have a sufficient amount of that particular bacteria.

      As I've discussed in numerous other posts (search "probiotics") on this website, diet and lifestyle factors can alter the bacterial composition in a person. So in order to minimize this factor, my idea was to pre-metabolize these ginsenosides and sell the resulting compounds. To make a long-story short, the project never went anywhere--but I have come across at least one company who's taken this idea and commercialized it.

      Good stuff? It'll get way better. Just watch.

  2. I wanted to add to this discussion with another few points made by Julian Whitaker, MD.

    Dr. Whitaker points out that a pound of steak only contains about 400 mg of L-carnitine, of which, only a small percentage will get converted to TMAO. On the other hand, a pound of fish, will have 1700 mg of PRE-FORMED TMAO. So while fish contains many, many more times the amount of TMAO, study after study show that fish consumption protects cardiovascular health.

    Further, the dose of L-carnitine used in the study would equate to 26,000 mg/day in a human. Most will only consume 500-1000 mg/day from supplements, with some human studies using up to 3000 mg/day. No one in their right mind would take 26,000 mg daily!

    So now you've got more points to poke holes in this disgraceful study. Anyone who references this L-carnitine study as holding any significant weight should lose their credibility.


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