new NYT article on red meat
Lean steak is low in fat and cholesterol and high in protein ??? qualities normally considered healthy. But eating a lot of it can still cause heart disease. Researchers have now laid the blame on bacteria in the human gut that convert a common nutrient found in beef into a compound that may speed up the build-up of plaques in the arteries.
The results are published in Nature Medicine today. Co-author Stanley Hazen, head of cardiovascular medicine at the Cleveland Clinic in Ohio, says that the study could signal a new approach to diet and health. In some cases, an individual???s collection of intestinal microbes may be as important to their diet as anything on a nutrition label, he says. ???Bacteria make a whole slew of molecules from food,??? he says, ???and those molecules can have a huge effect on our metabolic processes.???
Consumption of red meat has been found to increase the risk of death from heart disease, even when controlling for levels of fat and cholesterol. To find out why, Hazen and his colleagues gave the nutrient l-carnitine ??? found in red meat and dairy products ??? to 77 volunteers, including 26 who were vegans or vegetarians. One committed vegan even agreed to eat a 200-gram sirloin steak.
Tests showed that consuming l-carnitine increased blood levels of trimethylamine-N-oxide (TMAO), a compound that, evidence suggests, can alter the metabolism of cholesterol and slow the removal of cholesterol that accumulates on arteries' walls.
But even when they took l-carnitine supplements, vegans and vegetarians made far less TMAO than meat eaters. Fecal 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.
To further make the case, researchers checked the levels of l-carnitine in the blood of nearly 2,600 people who were having elective heart check-ups. By itself, the nutrient didn???t seem to make a difference. However, people who had high levels of both l-carnitine and TMAO were prime targets for heart disease, further evidence that it???s the bacterial alchemy ??? not the l-carnitine alone ??? that poses the real threat.
Finally, the researchers found that feeding l-carnitine to mice doubled the animals' risk of developing arterial plaques, but only when the mice had their usual gut bacteria. When the animals were treated with gut-clearing antibiotics, l-carnitine in the diet did not encourage plaques.
Daniel Rader, director of preventive cardiovascular medicine at the University of Pennsylvania in Philadelphia, says that the study makes a ???fairly compelling??? case that intestinal bacteria feeding onl-carnitine increase the risk of heart disease.
The finding should give pause not only to meat lovers, but also to people who take l-carnitine supplements, which are marketed with the promise that they promote energy, weight loss and athletic performance, says Hazen. ???None of those claims have been proven,??? he says. ???I see no reason why anyone needs to take it.???
This article is reprinted with permission from Nature magazine. It was first published on April 7, 2013.
asked byMDiamond (30)
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on April 08, 2013
at 05:23 PM
The proof is in the pudding. If this info is accurate, then why do still extent hunter-gatherers have such low levels of heart disease? Why do Inuits eating a traditional diet that is almost exclusively meat and fat have none of the diseases of civilization? Why do the "paradox" cultures, such as the French, have such low heart disease rates? Obviously these studies are not done on paleo eaters so how did they control for massive consumption of carbs? They didn't. My guess is that this link will expand into a chain where high sugar environments encourage deleterious bacteria which then interact with carnatine to cause the very effect that all paleo research shows and that is that excessive carbs causes not only heart disease, but also stroke, Alzheimer's, arthritis, and diabetes.
This study is simply symptomatic of a scientific establishment that is conducting research based upon flawed premises. Start with what works--paleo--then compare our industrial food system to it. Not that hard. So much suffering could be averted.
on April 08, 2013
at 03:25 PM
This is indeed troubling. Everyone on paleo eats red meat and therefore consumes large amounts of carnitine. Some eating paleo also supplement with carnitine or acetyl l carnitine to increase energy or enhance brain function. Now this study which seems to be very straight forward in the negative effect TMAO exerts on plaque and heart disease. Surely we need more studies but if further studies indicate the same, paleos must be willing to question whether they are primarily paleo because it's "natural" or they are paleo because it is healthy (and enhances life span and risk of heart disease). If they answer that they are paleo because it optimizes life span (and the study is believed and replicated), paleos should abandon the consumption of red meat.
Btw, anyone who posts that this study is about optimized gut flora or that eating fruits and vegetables or cultured foods or probiotics will somehow prevent TMAO's effect on heart plaque has not read the study. Interestingly (but without all the mainstream press) Nature published a paper demonstrating that choline also promotes TMAO increasing heart disease: http://www.ncbi.nlm.nih.gov/pubmed/21475195 This study may also be relevant as us Paleos consume large amount of eggs and fish which are loaded with choline (and some of us supplement with choline, phosphatidylcholine or phosphatidylserine). Again choline (and derivatives) definitely promote brain function but possibly at the cost of future heart disease.
on April 09, 2013
at 11:47 AM
So many questions. What were the body fat levels of the people with higher TMAO?
How about the activity levels? Working out more uses up carnitine.
Do probiotics like kimchi etc modulate TMAO levels? Or is there another nutrient deficiency involved?
Grass fed versus Grain fed? How is TMAO getting into blood? lack of gut integrity?
There doesn't seem to be a common test for TMAO as a bio marker. is it worth including?
Should the risk of increased body fat indicate more or less of a risk than raised TMAO.
Waiting for Mat Lalonde, Chris Kessler, Robb Wolf, Chris Masterjohn, Dave Asprey etc to comment on this before getting very excited.
on April 10, 2013
at 05:56 PM
"The study itself, and even most of the media article about it, quite simply and without much fanfare stated that saturated fat and cholesterol have little to do with the supposed increase in heart disease observed with red meat consumption. Hold the press! Shouldn???t THAT be front-page news?!? Apparently not. Of course, they???re only willing to admit this publicly in the context of an article where they???re proposing yet another mechanism for how red meat will kill you."
Saturated fat and cholesterol have been condemned forever as causing heart disease. Here in this article, they're basically saying "we were wrong, but here's why red meat is still bad". If they were so wrong about saturated fat, couldn't they be wrong about their understanding of red meat and TMAO and risk of heart disease? I think Chris Kresser gives a pretty good analysis of the problems with the study.
on April 08, 2013
at 03:34 PM
Good catch, totally a coincidence though.
on April 08, 2013
at 03:24 PM
Oh, not again. Ok, first, if your gut flora is off, there are usually lots of issues in all areas. Hmmm... eating paleo (soluable fiber from leafy greens that has a prebiotic effect), or eating conventional (insoluable grains that do nothing and sugars and refined carbs that promote bad bacteria growth)... So, if you eat red meat and don't pay any attention to anything else you eat, it might actually be true.
On the other hand, from what I can gather, the Doublecheck on the mice used species that are genetically prone to high cholesterol buildup. I understand that you have to use mice that are sensitive for the things you're testing so you can see a difference, but in this case, these mice are known to have this reaction when given higher levels of cholesterol and meat, so they were just stacking the deck on this one.
Also, notice that the blame (secretly hidden in the text!) is on the bacteria problems, not necessarily the meat.
The takeaway is: eat the processed, high sugar, high carb standard American diet, and everything goes out of whack, messing up good foods as well!