Red meat + wrong bacteria = bad news for hearts : Nature News & Comment
Carnitine is actually a compound synthesized from amino acids and has an important biological role:
Carnitine - Wikipedia, the free encyclopedia
The claim seems actually to be that the action of certain strains of gut bacteria on L-carnitine can:
I say "seems" -- I didn't look up the references at the bottom of the article linked there to see whether I thought they had said what Nature thought they had.[increase] blood levels of trimethylamine-N-oxide ... a compound that, evidence suggests, can alter the metabolism of cholesterol and slow the removal of cholesterol that accumulates on arteries' walls.
Even if they had, should we rush away with the idea that the case is proved? After all for about the last fifty years we've been told that saturated fat is the problem. Was that true? Apparently not.
We're told "evidence suggests". Are you going to change your lifestyle on the basis of someone claim that "evidence" (not cited) ... "suggests". And, in truth, evidence cannot "suggest" anything. Only conscious, rational beings -- humans -- can make suggestions. But humans make mistakes ... and frequently jump to conclusions. Are their suggestions warranted here?
So, on the previous claims about saturated fat:
(My emphasis: and isn't that one to think about?)Results: During 5–23 y of follow-up of 347,747 subjects, 11,006 developed CHD or stroke. Intake of saturated fat was not associated with an increased risk of CHD, stroke, or CVD. The pooled relative risk estimates that compared extreme quantiles of saturated fat intake were 1.07 (95% CI: 0.96, 1.19; P = 0.22) for CHD, 0.81 (95% CI: 0.62, 1.05; P = 0.11) for stroke, and 1.00 (95% CI: 0.89, 1.11; P = 0.95) for CVD. Consideration of age, sex, and study quality did not change the results.
Conclusions: A meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD. More data are needed to elucidate whether CVD risks are likely to be influenced by the specific nutrients used to replace saturated fat.
Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease
So do we now hang our hats on this new suggestion? Or is it "once bitten, twice shy" ?
I think gut bacteria likely have all sorts of interesting effects on our health, and that we've but scratched the surface of that. I'm, nevertheless, suspicious of claims that people have worked out once for all that they are implicated in this particular problem in just this particular way.
I'm inclined to think that behind this claim, apart from anything else, there's likely to be an emotional reluctance to drop the shaky claim that "red meat" is problematic in one way or another -- if not in way x, then in way y, or in any other way someone can dream up. Note what's said in the linked article:
But are vegetarians and vegans generally healthier than people eating a mixed diet? There's a heck of a lot of good evidence that quite unequivocally shows otherwise. See Cordain's latest book for more on that:But even when they took l-carnitine supplements, vegans and vegetarians made far less TMAO than meat eaters. Faecal studies showed that meat eaters and non-meat eaters also had very different types of bacteria in their guts. Hazen says that a regular diet of meat probably encourages the growth of bacteria that can turn l-carnitine into TMAO.
The Paleo Answer: 7 Days to Lose Weight, Feel Great, Stay Young: Loren Cordain: 9781118404157: Amazon.com: Books
One can find studies that appear to indicate that "red meat" is "unhealthy" in a number of ways if one tries hard enough. But then you have to ask: "How well did those studies control for other factors?" See here:
Science, Pseudoscience, Nutritional Epidemiology, and Meat
In conclusion, it's an interesting suggestion. I'm not claiming any expertise in the area, but I will say that it seems to me that nothing has been proved, to say the least. I'd be interested to know what other people here think. It looks to me like people desperately grabbing a secondary hypothesis (namely that the action of bacteria on L-carnitine is problematic) in order to keep a rusty old clapped-out primary hypothesis (namely that red meat is problematic) on the road.
And, even if it is true -- which, I repeat, we don't know -- might it not be possible that some other factor in one's diet -- eating the stomach contents of ruminant animals; eating putrid meat; eating organ meats; eating bitter herbs ... or dirt .. or who knows what? -- might change the bacteria and completely change the problem? Heck, what might be the effect on antibiotics or antibacterial hand-cleaners on the gut microbiome?
Some primitive societies lived on almost nothing other than meat from game animals, at least at certain seasons of the year, and seem to have been very healthy on it. North American Plains Indians are a good example:
Guts and Grease: The Diet of Native Americans - Weston A Price Foundation