People who eat more red meat get a lot more cardiovascular disease than most other people. Doctors believe that red meat has lots of saturated fats and cholesterol, which causes cardiovascular disease. But it is not that simple. As science develops, the attention is going to intestinal bacteria. Their importance has only been acknowledged in the past twenty years or so, but they have already been shown to impact such vital physiological processes as immune function and the development of cancer, diabetes, and obesity. Dietary choices—like those to eat red meat or not—are known to influence the relative ratios of the different bacterial species residing in our guts.
So researchers at the Cleveland Clinic decided to check out how different intestinal bacteria metabolize the components of meat. They found that bacteria present in the intestines of omnivores, but not present in the intestines of vegans or vegetarians, generate a molecule that promotes atherosclerosis when they are fed red meat.
Dr. Hazen is the chairman of the department of cellular and molecular medicine at the Lerner Research Institute of the Cleveland Clinic, a prestigious academic medical centre. He and his colleagues have accumulated evidence for a surprising new explanation of why red meats like beef and pork may contribute to heart disease. The researchers had come to believe that what damaged hearts was not just the fat on steaks, or the marbling of their interiors. In fact, these scientists suspected that saturated fat and cholesterol made only a minor contribution to the increased amount of heart disease seen in red-meat eaters. They began their research five years ago with a study of 10,000 people at risk for heart disease who agreed to provide blood samples and to be followed so the researchers would know if any patient had a heart attack or died of heart disease in the three years after the first visit. Those samples enabled them to look for small molecules in the blood to see whether any were associated with heart attacks or deaths.
The real culprit, they found was a little-studied chemical that is burped out by bacteria in the intestines after people eat red meat. It is quickly converted by the liver into yet another little-studied chemical called TMAO that gets into the blood and increases the risk of heart disease.
That study and a series of additional experiments on 2,595 people, led to the discovery that a red meat substance no one had suspected — carnitine — seemed to be the culprit. Carnitine is found in red meat and gets its name from the Latin word carnis, the root of carnivore. It is also found in other foods including fish and chicken and even dairy products. Red meat is the major source. Carnitine is a compound found in meat, hence the name carnitine. When fed Carnitine, meat eaters metabolize it to generate the product trimethylamine –N-oxide (TMAO).
The researchers found that carnitine was not dangerous by itself. Instead, the problem arose when it was metabolized by bacteria in the intestines and ended up as TMAO in the blood.
That led to the steak-eating study. An experiment was done: volunteers were fed steak. The question was: Would a burst of TMAO show up in people’s blood after they ate steak? And would the same thing happen to a vegan who had not eaten meat for at least a year and who consumed the same meal?
It turned out that within a couple of hours of a regular meat-eater having a steak, TMAO levels in the blood soared.
But the outcome was quite different when a vegan ate a steak. Researchers had hypothesized that vegans would not have as many of the gut bacteria needed to make TMAO, and indeed virtually no TMAO appeared in the vegan’s blood after he consumed a steak.
And TMAO levels turned out to predict heart attack risk in humans, the researchers found. The researchers also found that TMAO actually caused heart disease in mice. Additional studies with 23 vegetarians and vegans and 51 meat eaters showed that meat eaters normally had more TMAO in their blood and that they, unlike those who spurned meat, readily made TMAO after swallowing pills with carnitine , a substance found in red meat.
Researchers say the work could lead to a new way to assess heart disease risk by looking for TMAO in the blood.
Are people with high blood carnitine or TMAO levels at higher heart disease risk and its effects – heart attack, stroke and death? They analysed blood from more than 2,500 people, asking if carnitine or TMAO levels predicted heart attacks independently of traditional risk factors like smoking, high cholesterol and blood pressure. Both carnitine and TMAO did. On further analysis, they discovered that the effect was solely because of TMAO.
The researchers’ theory, based on their studies, is that TMAO enables cholesterol to get into artery walls and also prevents the body from excreting excess cholesterol.
What is it about carnitine that bacteria like? The answer is that bacteria use it as fuel.
Would people reduce their heart attack risk if they lowered their blood TMAO levels? There also are questions about the safety of supplements like energy drinks and those used in body building. Carnitine is often added to energy drinks on the assumption that is will speed fat metabolism and increase a person’s energy level.
The investigators’ extensive experiments in both humans and animals, published in Nature Medicine, have persuaded scientists to seriously consider this new theory of why red meat might be bad for people.
You need to stop doing this damage to yourself. It is as if you were paying to eat to destroy your body. Does that make sense?
Maneka Sanjay Gandhi
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