Carnitine, Red Meat, TMAO & CVD
This is red meat week!
If you haven’t heard about it by now, a new paper was released this week looking at the link between carnitine, gut bacteria, a molecule called TMAO, and atherosclerosis. The multi-part study was performed by researchers at the Cleveland Clinic, among other places, and was reported in the New York Times, Culprit in Heart Disease Goes Beyond Meat’s Fat, and today’s episode of Science Friday, Red Meat’s Heart Risk Goes Beyond the Fat (1).
The Science Friday episode is 13 minutes long and is a good overview of the research, though I will go over it here briefly.
Carnitine is an amino acid (but not a protein amino acid) that is used by the body to transport fatty acids into the cell’s mitochondria to be burned as energy. For this reason, there have been many trials of carnitine supplementation with hopes that it could increase fat loss and related conditions. The trails have been mixed (1). In food, carnitine is found in the highest amounts in beef (56-162 mg per 4 oz serving according to the NIH), while other foods have much lower amounts (a chicken breast has only 3-5 mg per 4 oz).
While humans can produce carnitine, and most people can produce all they need, only bacteria can break it down (1). Some bacteria convert carnitine into a molecule called trimethylamine (TMA) and when this happens, the liver converts TMA to trimethylamine-N-oxide (TMAO).
In 2011, in the VeganHealth.org article, Choline, I reported on a study by this same group of researchers that indicated that the metabolism of choline, by gut bacteria and then the liver, results in TMAO. The researchers found that high blood levels of TMAO were associated with cardiovascular disease.
This time, they studied carnitine rather than choline, and they came to a similar conclusions. They also found that vegetarians do not have the bacteria in their guts needed to produce TMAO out of carnitine; not that this really matters given that we eat little to no carnitine.
Based on their studies using mice :(, the researchers believe that TMAO prevents the metabolism of cholesterol by the liver and diverts it to the blood vessels where it becomes plaque.
In my series Of Meat and Mortality, I did not mention that the Harvard study found that saturated fat and cholesterol in red meat only moderately accounted for the increase in cardiovascular disease associated with red meat. This theory about TMAO causing heart disease might explain the finding by Harvard and also help explain why poultry has not had an association with mortality from cardiovascular disease while red meat has.
This is not the final word on carnitine and heart disease and it will be interesting to see what future research shows.
Reference
1. Koeth RA, Wang Z, Levison BS, Buffa JA, Org E, Sheehy BT, Britt EB, Fu X, Wu Y, Li L, Smith JD, Didonato JA, Chen J, Li H, Wu GD, Lewis JD, Warrier M, Brown JM, Krauss RM, Tang WH, Bushman FD, Lusis AJ, Hazen SL. Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013 Apr 7. doi: 10.1038/nm.3145. [Epub ahead of print] | link
April 13th, 2013 at 4:45 am
It seems the future research is already here and it shows exactly the opposite: http://j.mp/12VCsjF. I can’t find the study, though. Perhaps it will be published directly in the June issue.
April 13th, 2013 at 5:01 am
Is there a problem with taking L-Carnitine supplements? I originally was taking them for benign irregular heartbeats (PVCs) and was told by a cardiologist it was fine to keep taking them. I take 500 mg daily but am wondering if it might be best to DC that since I no longer have PVCs.
April 22nd, 2013 at 6:36 pm
Marion,
It is not clear if a vegan taking carnitine supplements would see an increase in the bacteria that create TMAO. I would ask your doctor about it again.
April 16th, 2013 at 7:32 am
Carnitine is also found in cheese (hi there dr. barnard) and tempeh.
@marion, randomized double blind studies of just about every supplement have shown either no effect or a slight negative impact on health. imo, any physician who is promoting supplements should revisit their oath.
April 22nd, 2013 at 8:38 pm
another_vegan_scientist,
Are you suggesting, for example, people with vitamin D deficiency shouldn’t take vitamin D supplements? Some vegans cannot thrive without carnitine supplements. But perhaps you just mean that there are no nutrition supplements that reduce chronic disease in the general population.
April 18th, 2013 at 5:57 am
In addition to carnitine supplements, what about choline supplements? Should we just avoid both and make sure to eat foods such as soy which are high in lysine, methionine, and choline?
April 22nd, 2013 at 8:24 pm
Brandon,
I don’t think choline supplements are necessary for most vegans. More info and good sources of choline:
http://veganhealth.org/articles/choline
April 23rd, 2013 at 10:33 am
I didn’t feel any different taking 500mg l-carnitine (though it was the regular version not acetyl-l-carnitine, maybe that would make a difference). I took carnitine supplements just to see if it would do anything (I did same for 500mg taurine and also felt no different). I also didn’t feel different taking a supplement of 250mg choline (and 250 inositol in the same pill). I need to calculate my dietary choline consumption in order to figure out how much I’m getting. Your food diary on the VeganHealth.org choline page though is similar to what I’d probably eat in a day.
April 23rd, 2013 at 10:35 am
Brandon,
I also just did an experiment taking 500 mg of taurine per day for about a month and felt no different. I hope to make a quick post about it this week.
April 23rd, 2013 at 7:18 pm
Andrei,
My response to the carnitine meta-analysis:
http://jacknorrisrd.com/follow-up-to-carnitine-and-atherosclerosis/
May 4th, 2013 at 11:10 am
Update: I’ve taken acetyl-l-carnitine at the levels from 250 mg – 750 mg daily for the last 8 days and, unlike l-carnitine which I didn’t feel anything, the acetyl form makes me feel bad. It’s causing heart palpitations and I have no history of any heart problems. I’m stopping this now and dumping the rest of the bottle. I will go the safe (and free!) route of just eating food and having my body produce whatever carnitine is needed on it’s own.