Bad News for Red Meat: Well, read the fine print
There are more bacteria in your colon than people on planet earth. Without bacteria people couldn’t survive or thrive. Bacteria are responsible for us being able to get vitamins, they break down fiber into chemicals that protect us against colon cancer. Now, in a study recently published in Nature, proposing that red meat leads to heart disease through bacteria.
The mechanism is a byproduct of the metabolism of some bacteria called TMAO (trimethylamine N-oxide) which, in some studies, is correlated with an increased risk of heart disease.
In the experiments conducted they took meat eaters and vegans and fed them steaks. Why I wasn’t invited to participate is clearly an oversight – after all, steaks…. They discovered when red meat eaters ate steak their level of TMAO went up, but not if vegetarians ate it. They even discovered it wasn’t the meat, but rather the carnitine in the meat that did this (a common supplement in protein drinks for those who want to look like Arnold Schwartzeneger on steroids).
Takes a bit of presumption doesn’t it. But lets work backwards from this hypothesis and start with a favorite saying:
Correlation does not equal Causation
The evidence that red meat causes an increase in coronary artery disease is mixed, at best. The latest study showed there was no evidence that this was an independent risk factor. Smaller studies such as the Nurses Health Study and Health Professional Follow-up study showed an association with a relative risk factor of much less than 2. I blogged a summary of those studies.
Your Gut and Bugs
The bacteria in your gut are important. They protect you- by simply occupying space, they prevent bacteria that are harmful to you from finding a home, as well as parasites, yeast, and perhaps some viruses. It has been estimated we have over four pounds of bacteria in our gut. Just a few other numbers that are fun: it is estimated there are over 100 trillion bacteria in our gut (the human being is made up of about 10 trillion cells, so there are more of them than there are of us – or, a philosopher might ask – who are we really). We have grown only about 70% of the bugs found in our gut, or so we guess. The byproducts of these bacteria include chemicals that prevent fungus from taking hold, prevent other bacteria from getting close, and they alter the pH of the gut to keep it comfortable for us and our friendly bacteria, but not so much for the bad bacteria.
These friendly bacteria help produce vitamin K, and biotin. In addition to helping ferment other substances that our body cannot break down, and by breaking down those substances make them available for us to get nutrients from them. While humans cannot digest fiber, some of the bacteria in the gut can digest fiber, and the byproduct of that digested fiber is an agent that decreases the risk of colon cancer (our poop has stuff that bacteria eat and bacteria poop keep us from getting cancer). Is it possible that the bacteria in our gut could create something that makes it more likely for us to have heart disease, or cancer? Yes, it is quite possible. What you eat does alter your gut bacteria. Who you kiss alters your gut bacteria. Who your parents are alter your gut bacteria. When you get an antibiotic, your gut bacteria change.
With some antibiotics and a combination of stomach acid reducing agents (Prevacid, Nexium, etc) a bacteria that overgrows the colon called Clostridium difficile (C diff). This bacteria so overgrows the colon and as a result people can develop ulcers, bleeding, toxic mega-colon, and perforation as well as death. This is a concern for surgeons, something we encounter far too often.
Some people can get overgrowth of bacteria in their small bowel that can lead to malabsorption of nutrients including bloating, nausea, diarrhea, constipation, and long term problems like anemia from iron malabsorption, and has been linked with some auto immune diseases.
Think of your gut like an eco-system. If it is in perfect harmony, you benefit from it. If not, an overgrowth of one or another bacteria can lead to problems.
Diet certainly affects which bacteria inhabit your gut. The big question remains, is there a diet, or set of foods, that will encourage the gut to have more “friendly” bacteria and less “bad” bacteria. Here is the realm of speculation – other than a diet rich in fiber being healthy, we don’t have a great answer. This doesn’t stop people from speculating about one diet or another being better. In this case, the speculation would be that vegans and vegetarians eat a diet that keeps the bacteria that produce TMAO to a minimum.
And the colon- remember, people have been telling you for years about how bad the colon is- from Kellog and his enemas (he died in his 60′s from heart disease, was a perfect vegetarian and loved colonics) to modern day colon cleansers. No doubt there will be on Walgreen’s supplement shelves a pro-biotic that will get rid of the bugs that make TMAO.
Gut bugs and Diet
There are three types of gut flora that have been described based on the diet that people have. The “enterotypes” are descried as Prevotella, Bacteroides, and Ruminococcus. Each one associated with a specific type of diet. Prevotella comes from diets with lots of simple sugars, or high-glycemic index carbohydrates. Bacteroides is associated with animal proteins, or the typical western diet. It is those people who have the Prevotella species that had a higher TMAO blood level. Oddly 3 our of 4 of the subjects that had the Prevotella species were omnivores.
In another study showed that these broad enterotypes were associated with long-term diets. When people were fed a controlled diet the enterotypes remained the same during the ten day study. While some bugs changed quickly, it appears your gut ecology takes a while to change – which, if you think about it, is not surprising.
You are probably thinking- 100 trillion bacteria, and the population of some types more than others? Think of the United States with its population and other countries with their population. In Norwegian countries there are more Scandinavians, in Italy there are more Latins – now think of your gut. In Vegans, there are going to be more bacteria that do well with their host who eats vegetables – and in omnivores, the bacteria that populate it will likely be more of those that like chewing on remnants of meat. The hypothesis here is that those bacteria produce more TMAO, and thus meat eaters, when given meat, make that harmful substance that leads to more cardiac deaths (forget that this is a poor correlation in any study looked at, just go with it for a bit). Now- bacteria don’t just eat meat and poop out TMAO – there are enzymes involved in the conversion to this “deadly” substance – and one of them is Vitamin B2, which is typically LOW in vegetarians.
What about TMAO and the Nature Article?
One arm of the human study was with six people. Five of them were meat eaters and there was one vegan. This is little more than an observation, and hardly enough of an observation to make headlines. That one vegan didn’t make TMAO means nothing. It could be that the vegan had antibiotics recently, it could be that they are an exception, it could be a lot of things. The one vegan was a male, and the non-vegans were females – and when the statistics were examined carefully – well, not a difference. But significant, even as an observation – nope.
Of course of the 23 vegans/vegetarians and 30 omnivores they looked at the bacteria in their stool (reminds me of the movie The Madness of King George – when they were obsessed with his stool) – and found the different types of bacteria attempting to correlate those bacteria with meat eaters or vegetarians. The problem was, some of the individuals with the “good bacteria” were omnivores.
The Nature article also looked at a mouse study. Mice are not humans, but with mice they didn’t feed them steaks. Instead they used carnitine. Carnitine is an amino acid, often used in supplements, but your body makes this amino acid naturally. To date there have not been studies that show that carnitine rich foods increase TMAO, in fact the one food that elevates TMAO is some seafood. Seafood, by the way, is associated with decreased risk of heart attack.
In the mouse study they fed them enough carnitine to the equivalent of a human eating about a thousand steaks a day. And I would submit if you eat that many steaks a day you might have some problems. The other issue is this: the gut bacteria of the mouse are not the same as the gut bacteria of the human. Are you a man or a mouse can apparently be answered by checking your fecal bacteria.
AND NOW EGGS?
It is the same argument and discussion for eggs. Turns out that the correlation with eggs and heart disease is zip. In fact, one of our patients finished a month of eating nothing but eggs and saw his cholesterol drop! Again, this is just a bad article with a lot of bad press.
A House of Cards
This study and news report is a part of a house of cards. Conclusions built upon conclusions, with a benign observation from one vegan, and a study in mice. In their conclusion the Nature paper stated that this went along with evidence of risk reduction for non red meat eaters and they cited the Mediterranean diet study in NEJM. What they fail to grasp is that diet didn’t show a decrease in heart attacks, or heart related events, only a decrease in risk of dying from a stroke – and no absolute decreased risk of dying.
This study again falls into the “red meat is bad,” and shows two things: studies that make headlines in newspapers show that in the slow death spiral of print media they fired their science reporters first and second, if you want your study to get headlines, find something that shows what the popular press thinks is true.
Saturated fat and cholesterol in beef don’t cause heart problems, and your body makes more carnitine than you get from your diet by a factor of six (unless you are a mouse that is force fed). TMAO is a huge byproduct of fish, and fish eaters seem to have longer lives and less heart disease.
So- this study make sense to you? Is there maybe a message here? One thing is certain: vegetables are not bad things for you. While some of the omnivores in this group had “good gut bacteria” it could be because they ate a lot of vegetables. So- if I were you, I’d make sure I had plenty of that good old fashioned fiber in my diet. Who knows, maybe that helps the good bacteria from having heart attacks.
The red meat article, published originally on Nature.com
Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013 Apr 7 Koeth RA, Wang Z, Levison BS, Buffa JA, Org E, Sheehy BT, Britt EB, Fu X, Wu Y, Li L, Smith JD, Didonato JA, Chen J, Li H, Wu GD, Lewis JD, Warrier M, Brown JM, Krauss RM, Tang WH, Bushman FD, Lusis AJ, Hazen SL. PMID: 23563705
Here is the article showing that fish and other sea products give rise to increases in TMAO more than meats.
Dietary precursors of trimethylamine in man: a pilot study. Food Chem Toxicol. 1999 May;37(5):515-20. Zhang AQ, Mitchell SC, Smith RL. PMID: 10456680
Here is an outstanding article by Chris Masterjohn that gives a far more in depth analysis than I did.