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Carnitine 'Damages heart'

Carnitine 'Damages heart'

Over time, we have seen L-carnitine mentioned quite a number of times. As well as the more general issues of appropriate diets.

Today a specific story relates why red meat might specifically be an issue - and the taking of L-carnitine, lecithin, choline or betaine supplements (see towards end of story).

The article in Nature is, as so often, behind a paywall wanting $22 to be allowed to view it. :-(

There are pertinent links and comments on the original BBC page - link at end.

8 April 2013 Last updated at 01:08

Red meat chemical 'damages heart', say US scientists

By James Gallagher Health and science reporter, BBC News

A chemical found in red meat helps explain why eating too much steak, mince and bacon is bad for the heart, say US scientists.

A study in the journal Nature Medicine showed that carnitine in red meat was broken down by bacteria in the gut.

This kicked off a chain of events that resulted in higher levels of cholesterol and an increased risk of heart disease.

Dieticians warned there may be a risk to people taking carnitine supplements.

There has been a wealth of studies suggesting that regularly eating red meat may be damaging to health.

In the UK, the government recommends eating no more than 70g of red or processed meat a day - the equivalent of two slices of bacon.

Saturated fat and the way processed meat is preserved are thought to contribute to heart problems. However, this was not thought to be the whole story.

"The cholesterol and saturated fat content of lean red meat is not that high, there's something else contributing to increases in cardiovascular risk," lead researcher Dr Stanley Hazen told the BBC.

Gut bugs

Experiments on mice and people showed that bacteria in the gut could eat carnitine.

Carnitine was broken down into a gas, which was converted in the liver to a chemical called TMAO.

In the study, TMAO was strongly linked with the build-up of fatty deposits in blood vessels, which can lead to heart disease and death.

Dr Hazen, from the Cleveland Clinic, said TMAO was often ignored: "It may be a waste product but it is significantly influencing cholesterol metabolism and the net effect leads to an accumulation of cholesterol.

"The findings support the idea that less red meat is better.

"I used to have red meat five days out of seven, now I have cut it way back to less than once every two weeks or so."

He said the findings raised the idea of using a probiotic yogurt to change the balance of bacteria in the gut.

Reducing the number of bacteria that feed on carnitine would in theory reduce the health risks of red meat.

Vegetarians naturally have fewer bacteria which are able to break down carnitine than meat-eaters.

Victoria Taylor, Senior Dietitian at the British Heart Foundation, said: "This is certainly an interesting discovery and sheds some light on why red meat might have an impact on heart health.

"While the findings won't necessarily mean a change to existing recommendations, these scientists have served up a good reminder for us to think about alternative sources of protein if we regularly eat a lot of red or processed meats."

Catherine Collins, a dietitian at St George's Hospital, said: "It's a very persuasive argument, but we know that eating a couple of portions of red meat weekly is of no risk, heart wise.

"There's no need to change our dietary recommendations from this - a Mediterranean-style diet with modest meat, fish, dairy and alcohol intake, coupled with more pulses, vegetables fruits, wholegrains and mono-unsaturated fats, remains the nutritional blueprint for a healthy and healthful life.

"But I would strongly recommend that unless you're a vegetarian or vegan, there is a potential risk from taking L-carnitine, lecithin, choline or betaine supplements in an attempt to ward off cognitive decline or improve fat metabolism.

"If the evidence is confirmed these supplements would do more to damage arteries than provide health benefits."


Picture is of Bürgermeisterstück (tail of rump).

16 Replies

Interesting. Is this the cholesterol story all over again? I can't read enough and wouldn't understand enough anyway to know whether this is another byproduct of a disease process rather than a cause.

Why is the recommendation against lecithin, choline and betaine? It's not clear to me how they relate to L-carnitine?


Nor me!

Another case in which what has been presented to us does not explain adequately.

The way the story is written suggests that it is the person's AIM in taking the supplements which causes the problems, not the mere fact of taking them! If you take them in an attempt to ward off cognitive decline or improve fat metabolism they are not good. Otherwise they are fine???? :-)

And don't we all know that thyroid hormone is the way to improve fat metabolism? (Meant as a joke but with quite some truth behind it.)



What I understood from this is that cholesterol and saturated fat are a problem only because the by-product of carnitine breakdown affects the way the body deals with them, not that they are a problem on their own.

That's my understanding anyway ;)


I don't think this study looked at mechanisms involving fat or cholesterol. The idea that it might influence arterial plaque formation is just a hypothesis from what I can see - where they try to link the new ideas with the old.

(I don't believe that saturated fat and cholesterol cause heart disease, but that's another story.)

The write up in Nature news points out that its not carnitine that's the problem on its own, but high levels of TMAO. L-carnitine is synthesised in the human body too, so levels in the body are constant pretty much regardless of what you eat, it says.

If high levels of bacteria are found in the gut that can metabolise carnitine into TMAO, does that mean that it's the meat eating that is the problem, or is it more of an issue that incompletely digested food particles are reaching the large intestine?

There's been a lot of research into the benefits of L-carnitine and its protective effects in people who have previously suffered a heart attack. To be honest, I think I'm more confused now than I was before I read the article properly!


Thanks for clearing that up. I agree that cholesterol and saturated fat are not the problem (in fact it looks like not enough might be more of a problem!) and that it is the TMAO that's the problem. I wonder if you are right about the bacteria in combination with the undigested food being the issue rather than the red meat. Perhaps if we ate more naturally reared red meat there would be less of a problem.

Thanks for the info. Greatly appreciated :)


sorry but I'll eat meat anyway, (biased as farmer's daughter and married to ex butcher) a lot of cultures save the best for their kids, invalids and elderly, i.e. meat. I wonder why.

Suppose it's a good excuse to create alternative sources of protein, fine but I'd rather have the real stuff with minimum processing and not as supplements (if anyone prefers alternatives that's fine too - everyone has a choice).

Cereals make animals fat, giving them fat makes them lean and eat less - strange eh? J :D



Jo xx


I found this online and am having a weird sense of deja vu:

It's the same set of researchers, although now they are saying that certain bacteria metabolise L-carnitine, whereas before they were saying that these bacteria metabolise choline.

I think the analysis by Chris Masterjohn applies equally to the new research.

He says the highest food source of precursors to TMAO is fish!

Why, oh why is virtually all the science reporting on this so rubbish?


Oh! That darned deja vu again? :-)

The answer appears to lie some where in the region of journos getting paid because of the reaction they produce rather than the quality transfer of information.

Thanks for the addition of that information.



Oh ****, do you think that includes Betaine Hydrochloride taken for low stomach acid?


I think it does. But without any further explanation it makes no sense.


Thanks - just when I was thinking how effective betaine hydrochloride was!


Definitely don't change on the basis of that article!

It is quite possible that the positives of taking it are more important that the suggested negatives. Impossible to judge without more info. :-(



You're right of course. I won't stop taking it for now, but will keep an eye open for further evidence.



One of my favourite online authors has just published an article giving his thoughts on the subject. Worth reading in my opinion :)

Red Meat and TMAO: Cause for Concern, or Another Red Herring?



Loads of reports are out now. This one is slightly less reserved in its condemnation of the research as a load of b******ks.

Yay for red meat :-)


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