Will Eating Meat Really Increase Your Risk of Heart Disease?
Nearly 100 trillion bacteria, fungi, viruses and other microorganisms compose your body’s microflora, and it’s becoming increasingly clear that these tiny organisms play a major role in your health.
Gut microbes are particularly prominent in the news lately, and one of the most talked-about studies suggests bacteria in your gut may play a role in your risk of heart disease through a surprising mechanism: the breakdown of a widely consumed compound in protein known as L-carnitine.
As a result, the media has mounted a virtual campaign warning that red meat eaters may be at higher risk of heart disease. But does the research really back up that claim? Some nutritional experts disagree, pointing out the many weaknesses in the study, and why giving up meat to prevent heart disease may be premature, if not downright wrong.
This 6 person study may be one of the worst and most publicized since last year’s media attack stating eggs were as bad for you as smoking.
Microflora Composition–A New Explanation for the Link Between Red Meat and Heart Disease?
It’s widely stated that eating red meat causes heart disease, an association that is often blamed (incorrectly) on its impact on cholesterol levels. Yet, research has repeatedly shown that the dietary cholesterol-heart disease connection is incorrect.
So while the featured study may offer intriguing clues to the importance of gut bacteria, and how gut bacteria is influenced by your diet, it’s doubtful that this latest hypothesis linking heart disease to red meat consumption via another pathway is entirely correct.
For example, a 2010 study from Harvard found no evidence that eating red meats leads to heart disease.1
That said, the featured study published in Nature Medicine2 claims to shed some light on why some people who eat red meat develop heart disease while others do not – and the reason may come down to differences in gut bacteria.
The study,3 by researchers from the Cleveland Clinic, found that human gut bacteria can metabolize L-carnitine, a substance found in red meat, energy drinks and dietary supplements, and in so doing produce a byproduct called trimethylamine-N-oxide (TMAO). TMAO is thought to encourage fatty plaque deposits to form within arteries (atherosclerosis), and therefore, the more TMAO you have in your blood the greater your risk of heart disease might be.
Interestingly, people with diets high in L-carnitine, i.e. meat eaters, had a gut microbe composition that was more prone to forming TMAO, while vegetarians and vegans did not. Even after consuming large amounts of L-carnitine in a steak or supplement, the vegetarians and vegans in the study did not produce significant amounts of TMAO.
This, the authors believe, means that eating red meat alters your gut flora in a way that predisposes your body toward TMAO production, and subsequently, heart disease. This was confirmed by giving the omnivores a course of antibiotics, after which they did not produce TMAO. Stanley Hazen, MD, PhD, the study’s lead author, said in a statement:4
“The bacteria living in our digestive tracts are dictated by our long-term dietary patterns… A diet high in carnitine actually shifts our gut microbe composition to those that like carnitine, making meat eaters even more susceptible to forming TMAO and its artery-clogging effects.”
Is Red Meat Being Inaccurately Singled Out as a Heart Disease Promoter?
The latest study is not the first to link gut bacteria to heart disease. In 2011, the same researchers, Hazen and colleagues, used data from nearly 2,000 people and showed that when the bacteria in your gut break down lecithin, a type of fat found in meat, eggs, dairy and other animal foods along with baked goods and dietary supplements, and its metabolite choline, it also leads to the creation of TMAO and, subsequently, increases your risk of heart disease.5
In response to this and the current study, many have wondered whether red meat and other animal foods, along with supplements containing L-carnitine, lecithin or choline should be avoided. Chris Masterjohn PhD, who is currently researching fat-soluble supplements at the University of Illinois, rebutted the 2011 findings stating:6
“…previous studies have shown that supplements with salts of free choline do in fact generate TMAO, but uncontaminated phosphatidylcholine, the main form of choline found in food, does not. Moreover, choline-rich foods like liver and eggs did not produce more TMAO than a control breakfast, but seafood, which is generally contaminated with some trimethylamine or TMAO, did.”
Masterjohn also disagrees with the group’s latest findings, in which the researchers claim that carnitine in red meat contributes to heart disease via the same pathway, i.e. the creation of TMAO. According to Masterjohn, incomplete reporting of data in the paper combined with “wild runaway inferences” by the press has generated a grossly misleading picture of red meat’s impact on heart disease, while simultaneously ignoring the food group that actually generates the most TMAO.
He points out that red meat is only one of many foods that increases TMAO when eaten, and cites data from a 1999 study that evaluated TMAO excretion following consumption of 46 different foods, which shows that red meat generated no more TMAO than fruits and vegetables. In fact, some veggies, such as peas, cauliflower and carrots generated more TMAO than beef did! Still, none of the foods generated TMAO at levels that were statistically different from the control. (Similarly, there was no statistically significant difference between different kinds of meats, compared to the control.)
Previous Research Shows Seafood Produces More TMAO than Any Other Food, Including Beef
The 1999 study did show however, one food group that stood out as a major source of TMAO, and that was seafood. Virtually all fish and invertebrates, with few exceptions (including trout and cockles) produced statistically significant more TMAO than the “light breakfast” control alone. And, according to Masterjohn’s own statistical test, all invertebrates except clams and cockles, and all fish except tuna, trout, plaice, and roe produced significantly more TMAO than beef. He writes:
“The single ‘representative female omnivore’ from the  Nature Medicine7 paper excreted similar amounts of TMAO in her urine as the six subjects from the 1999 study after consuming red meat, suggesting that, had they measured the response to seafood, the authors of the Nature Medicine paper would also have found much greater excretion of TMAO after consumption of seafood than after consumption of red meat
The difference between seafoods and red meat in the 1999 paper is like the difference between night and day. To take the most extreme example, halibut generated over 107 times as much TMAO as red meat. It seems obvious from this study that if any foods should be singled out for the production of TMAO, it should be seafoods. Yet the Nature Medicinepaper makes no mention of fish and the New York Times8 article only mentions fish to point out that it has less carnitine than red meat (and thus, by inference, will generate less TMAO, though that is clearly not the case, presumably because seafood tends to be contaminated with trimethylamine or TMAO itself…)
If we are to single out red meat as a source of TMAO, we should be able to identify other foods with which it should be replaced that generate less TMAO. Yet this 1999 study, which had a small sample size but tested an expansive number of foods, found that there basically are no other foods that generate meaningfully less TMAO than red meat.”
Axing Beef to Prevent Heart Disease Looks Like Another Red Herring…
Chris Kresser L.Ac has also weighed in on this issue,9 comparing the hypothesis that red meat causes heart disease via TMAO to the patently false notion that dietary cholesterol and saturated fat cause heart disease by raising serum cholesterol. Kresser lists three reasons for not taking the featured study at face value:
- Inconsistent epidemiological evidence
- “Healthy user” bias, and
- Inconclusive and insufficient evidence on the role of TMAO in heart disease
“…even if Paleo meat eaters have higher TMAO levels than vegans and vegetarians, we still don’t have evidence proving a causal relationship between TMAO and cardiovascular disease,” he writes. “Once again, the supposed link between cholesterol and saturated fat and heart disease should serve as a reminder not to jump to hasty conclusions that unnecessarily deprive people of nutrient-dense, healthy foods. It is virtually impossible to control for all of the possible confounding factors.”
You can read more of this article at:http://articles.mercola.com/sites/articles/archive/2013/04/22/eating-red-meat.aspx
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