Red meat chemical “damages heart”, say US scientists. BBC News (Health) 8th April 2013
Yesterday I was alerted to the following headline:
“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. Dietitians warned there may be a risk to people taking carnitine supplements.”
When I see a news article of this sort, I always want to dig a little deeper. It is easy for me to say, as a vegan and a scientist, “I told you so!” when headlines such as this hit our inboxes. This study found a chemical in meat that is reported to be bad for us, raising cholesterol levels and increasing atherosclerotic plaque in the blood vessels. I could have easily just told people that this is further proof that they shouldn’t be eating the stuff, but, even though the subject matter relates to meat, which I don’t suggest anyone eats, I want to know how the trial has been conducted and if there could have been any variables that might have influenced the validity of the study.
Certainly, looking at some of the comments posted on the BBC’s website following this article’s release, people are proclaiming it as nonsense. Personally, I disagree. Those who were rubbishing the study (I would guess, meat eaters themselves), were saying that it is only the way the meat has been processed that leads to these problems, and that, for example, organic grass reared meat would be different. This is a fallacy; all meat contains carnitine, regardless of how it is reared. For sure, organic grass reared animals don’t contain steroids, growth hormones, chemicals and antibiotics, but since consumers are eating the muscles of these creatures, by definition they are consuming carnitine in identical levels to those found in animals reared in any other way, so the organic argument here can be dismissed.
The BBC’s summary of the article relates how bacterial micro-organisms in the gut can consume carnitine and, in doing so, produce a gas, which is further converted in the liver to a compound known as TMAO (Trimethylamine-N-oxide). The article states: “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.” Strong words indeed. I could only access the abstract of the study, published in the journal Nature Medicine, since I am not a subscriber to that particular publication. My interpretation of the whole study is only based upon its abstract, so it could easily be that I have overlooked a key point that was not presented by this abstract. I was, however, a little surprised by the conclusions reached.
When I am looking at clinical studies, I always gauge their significance by considering the target species. Was the study performed on humans? If so, how was the dietary analysis performed? How many humans were in the study? Were they otherwise healthy, or were they subjects from a particular disease-affected group? If the study was performed on a laboratory animal species (rats, mice, guinea pigs, rabbits), can the findings be accurately extrapolated to the human model?
From the abstract of this study, it seems that the test subjects were humans, being evaluated for heart function, and mice, which had their diets supplemented with both TMAO and carnitine (the mice, being an herbivorous species, were not being fed red meat).
Carnitine supplementation in the mice led to alterations in the gut microbes, which in turn caused increased production of TMAO and higher levels of atherosclerosis. This did not occur if the gut bacteria were suppressed. In the human subjects, meat eaters produced more TMAO than vegetarians or vegans when they consumed L-carnitine, but the abstract does not state whether this L-carnitine was derived from the meat they were eating, or a supplement. In turn, blood levels of L-carnitine in the human subjects was a predictor for cardiovascular disease and infarction, stroke or death, but only if the subjects also had elevated TMAO.
Given that L-carnitine supplements are widely used by body builders and people who want to alter their fat to muscle ratios, and that they are being touted as helping with weight loss, as well as having antioxidant effects, perhaps we should now be questioning their use as a supplement, especially for meat eaters. The University of Maryland Medical Centre states that there is no scientific evidence to validate the claims that L-carnitine supports weight loss, improves athletic performance or the delays the onset of Alzheimer’s disease. And we know that there are many, many different antioxidants present in fruit and vegetables, so we don’t need to eat meat to get L-carnitine.
So where does this leave us in relation to the original BBC article? Is the mouse study relevant here? Mice do not have identical gut bacteria to humans. They are, after all, a totally different species, so why would they? Do meat eaters have a different gut flora from vegetarians or vegans? They may well have. Is a probiotic going to be of value? Probiotics are well known for their benefits for the immune system, but my recommended source would not be yogurt drinks, as the BBC article suggests, but a soil-based type in capsule form.
A representative from the British Heart Foundation stated that this study was “interesting” but unlikely to change their guidelines (in a previous blog post, I lamented the fact that despite a study indicating that red meat was proven to increase cancer rates, the British Heart Foundation’s response was that red meat can be enjoyed as part of a healthy diet).
Despite the potential shortcomings of this study, and the fact that I have to question the validity of extrapolation from the mouse model, I remain convinced that this is yet another nail in the coffin for the idea that eating red meat carries no associated health concerns. Whether it is in relation to cardiovascular disease risk, cancer risk or just meat consumption’s inherent unsustainability on a global scale, the case for adopting a vegan diet has just added a further ally.