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How Red Meat May Increase Heart Attack Risk

The 2015 Dietary Guidelines Advisory Committee has submitted recommendations for the 2015 edition of the Dietary Guidelines for Americans from the US government's Health and Human Services and the Department of Agriculture. The Guidelines state: " . . . the U.S. population should be encouraged and guided to consume dietary patterns that are rich in vegetables, fruit, whole grains, seafood, legumes, and nuts; moderate in low- and non-fat dairy products and alcohol (among adults); lower in red and processed meat; and low in sugar-sweetened foods and beverages and refined grains."

The government-appointed experts recommend restricting red meat, even though the news media in the past year has featured many articles that dietary cholesterol and dietary saturated fats do not cause disease. Many people now erroneously believe that:
• since red meat is full of saturated fat and cholesterol, and
• since dietary saturated fat and cholesterol may not be harmful,
• then it is safe to eat all the meat you want.

However, the majority of population studies show a strong association between eating red meat and increased risk for heart attacks, certain cancers and premature death. If cholesterol and saturated fats are not causing this increased risk, scientists need to find another reason and the answer may be TMAO, made by bacteria in your gut from the carnitine, choline, lecithin and creatine in red meat.

Dietary Cholesterol Has Not Been Shown to Cause Heart Attacks
In 1913, Russian pathologist, Nikolai N. Anichkov showed that feeding rabbits purified cholesterol dissolved in sunflower oil caused plaques to form in their arteries. However, no data on humans show that eating cholesterol causes plaques to form in arteries. Cholesterol does not enter plaques until long after the arteries are damaged. First, you get a hole in the inner lining of arteries, then bleeding, then clotting, and only then do plaques start to form and cholesterol starts to deposit in them.

Blood levels of cholesterol change very little when you eat foods that contain cholesterol. Less than 20 percent of the cholesterol in your bloodstream comes from the food that you eat. More than 80 percent is made by your liver. When you eat foods that contain cholesterol, your liver makes less and your blood cholesterol levels remain close to the same.

Eggs are one of the most concentrated sources of dietary cholesterol. However, blood cholesterol remains unchanged in more than 70 percent of people when two or three eggs a day are added to their diets (Curr Opin Clin Nutr Metab Care, 2006;9:8-12).

Dietary Saturated Fat May Not Increase Heart Attack Risk
The Kuopio Study (Arteriosclerosis, Thrombosis, and Vascular Biology, 12/04/14) and many other studies (Annals of Internal Medicine, March 2014) show that saturated fat from foods does not increase risk for heart attacks. The highest concentration of saturated fats occurs in three plant products, palm, palm kernel and coconut oils, and no data show that people who eat these plant sources of saturated fats are at increased risk for heart attacks.

However, many studies show that substituting polyunsaturated fats for saturated fats lowers cholesterol and reduces risk for heart attacks (PLoS Med, 2010 Mar 23;7(3):e1000252 and Am J Clin Nutr, 2011. Apr;93(4):684-8). A review of 11 American and European cohort studies showed that substituting unsaturated fats for saturated fats lowers cholesterol and helps to prevent heart attacks (Am J Clin Nutr, 2009 May;89(5):1425-32). The issue is not settled as there are conflicting reports. A review of 12 major studies shows that reducing fat intake (low-fat diets) does not prevent second heart attacks in people who have already had a heart attack. In other studies, substituting polyunsaturated fats (found primarily in plants) for saturated fats (found primarily in animal products) was not associated with reduced risk or heart attacks (BMJ Open, 2014 Apr 19;4(4):e004487).

Do Not Replace Saturated Fats with Carbohydrates
Replacing saturated fats with sugar and other refined carbohydrates such as bakery products and pastas increases heart attack risk. In the 1940s, Ancel Keys showed that people who have the highest levels of saturated fats in their bloodstreams are at increased risk for developing heart attacks. He did not know what we know now. Saturated fats in your bloodstream come from two sources: the saturated fat that you eat and the saturated fat that your liver makes. The saturated fats that you make in your own body:
* are called even-chain saturated fats,
* come from ingested sugar and alcohol, and
* are more harmful than the saturated fats called odd-chain that come from food you eat.

The largest study of its kind, from the University of Cambridge in the UK, shows that the saturated fats that increase risk for diabetes and heart attacks are even-chain saturated fats made primarily by the human liver from carbohydrates (primarily sugar and alcohol), and far less so from eating foods that are high in saturated fats (Lancet Diabetes & Endocrinology, published online August 6, 2014). Researchers followed 340,234 adults from eight European countries. Using high-speed blood analysis, they measured the types of saturated fats in the bloodstream and found that they could predict who would become diabetic by their high levels of even-chain saturated fats.

Many studies recommend replacing saturated fats with sources of polyunsaturated fats (vegetables, seeds and nuts) and minimally processed grains (wheat berries, rye berries, quinoa (Curr Atheroscler Rep, 2010 Nov; 12(6): 384–390).

How a Heart Attack Occurs
Heart attacks are not caused by blockage of an artery by progressive narrowing of that artery. First, a plaque breaks off from the lining of the artery. Then it travels down the ever-narrowing artery until it completely blocks blood flow through that artery leading to the heart muscle. That part of the heart muscle, unable to get its usual supply of blood, suffers from lack of oxygen which causes pain and eventually death to the part of the heart muscle starved of oxygen.

The TMAO Theory
Stanley Hazen at the Cleveland Clinic showed that feeding humans carnitine can increase blood levels of TMAO (TriMethylAmine Oxide), a chemical that can punch holes in arteries and increase the formation of arteriosclerotic plaques (Nature Medicine, published online April 7, 2013 and N Engl J Med, 2013;368:1575-1584). Bacteria in the intestines make TMAO from carnitine, choline, lecithin, creatine and creatinine, found in red meat, eggs, milk and dairy products, liver, poultry, shellfish, fish, sports supplements and protein drinks.

Carnitine is found in high levels in red meat and in much lower levels in fish, chicken and dairy products. Carnitine is a popular ingredient in sports supplements and protein drinks. Carnitine, itself, does not damage arteries; TMAO causes the damage.

Bacteria Form TMAO
Your intestines have huge colonies of hundreds of types of bacteria. Some of the types of bacteria in your intestines use carnitine to supply themselves with energy. They then convert the carnitine to another chemical called trimethylamine-N-oxide (TMAO). Earlier studies have shown that TMAO punches holes in the arteries of mice that start the formation of plaques in arteries.
• Blood TMAO levels rise very high after eating red meat in people who eat red meat regularly.
• Blood TMAO levels do not rise very high after vegans eat red meat.
• Certain types of bacteria convert carnitine to TMAO, the chemical that can cause plaques to form in arteries.
• When mice or humans are fed red meat, their intestines become overgrown with these bacteria that make TMAO.
• Vegans (people who eat no animal products) do not form TMAO after they eat red meat. Their intestines have extremely low levels of the bacteria that convert carnitine to TMAO.
• If you feed vegetarian mice large amounts of red meat, their intestines eventually overgrow with the bacteria that make TMAO.
• Mice fed large amounts of meat have large amounts of the bacteria that forms TMAO, high blood levels of TMAO, and increased risk for arteriosclerosis.
• Mice given antibiotics to prevent this bacterial overgrowth in the gut do not develop arteriosclerosis.

Over the last five years, Dr. Hazen has collected the blood of 10,000 patients at risk for heart disease. He has shown that those with high levels of TMAO are at increased risk for heart attacks. Other researchers have also saved blood samples from people who are vegetarians and those who are meat eaters. They will take these old blood samples and measure the level of TMAO in them. Then they can review the records of these people to confirm that the people with high levels of TMAO are the ones who suffer heart attacks, and that those with low levels are at low risk. We await further studies on humans to see if they confirm the results seen in mice.

Checked 3/9/16

March 1st, 2015
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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