New Research on Why Eating Meat is Associated with Heart Disease

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A study from the Cleveland Clinic and Tufts University found a 22 percent greater risk for heart disease for every 1.1 serving of meat per day (3.3 oz. cooked lean meat). This study followed more than 4,000 men and women older than 65 for an average of 12.5 years, and the increased heart attack risk was directly related to blood levels of TMAO and its precursors (Arteriosclerosis, Thrombosis, and Vascular Biology, Aug 1, 2022;42(9):e273–e288). TMAO comes from L-carnitine found in red meat. TMAO blood levels were a far better predictor of heart disease than high blood pressure or high cholesterol levels. This study found that fish, poultry, and eggs were not associated with increased risk for heart disease.

The same group of researchers found that higher levels of TMAO were associated with significantly increased risk for death from any cause, and death from heart attacks in particular (JAMA Network Open, May 20, 2022;5(5):e2213242). Other associated risk factors for heart disease included high blood sugar, high insulin and markers of inflammation.

Dozens of earlier studies have shown that eating mammal meat is associated with increased risk for heart attacks, strokes, certain cancers, diabetes and premature death (Circulation, April 22, 2019). The association between TMAO levels and heart disease may be stronger than with dietary saturated fat, cholesterol, sodium, nitrites, or high-temperature cooking.

TMAO and Heart Attack Risk
Meat is loaded with choline and carnitine, which pass to your colon where bacteria there convert them to a gas called trimethylamine (TMA) that is absorbed into the bloodstream and passes to the liver where liver enzymes convert TMA to TMAO. Choline and carnitine are found in large amounts in meat, in significantly lower amounts in poultry, fish, dairy, and egg yolks, and in very low amounts in plants. Mammal meat raises blood levels of TMAO much higher than poultry, and it also changes the bacteria in your colon to the ones that make TMA. When you switch from eating mammal meat to eating primarily chicken, fish and plants, blood levels of TMAO drop markedly as do the concentrations of colon bacteria that make TMA (Eur Heart J , Feb 14, 2019;40(7):583–594). The amount of saturated fat eaten had no effect on blood levels of TMAO (Am J Clin Nutr, 2021 May; 113(5): 1145–1156).

TMAO may increase risk of heart attacks by:
• reducing cholesterol clearance from the bloodstream,
• increasing cells that deposit cholesterol in plaques,
• increasing the cytokines that promote inflammation to form plaques, and
• increasing clotting that is the ultimate cause of heart attacks (Cell, March 24, 2016;165(1):111-124).

Other foods and supplements that contain the chemicals that can form TMAO include:
• Processed foods that contain phosphatidylcholine, also known as lecithin
• Dietary supplements that include choline or carnitine
• Energy drinks and protein supplements that contain lecithin or choline

Fish also contain carnitine and choline, and may slightly raise blood levels of TMAO. However, eating fish is not associated with increased risk for heart attacks (Microbial Ecology in Health and Disease, May 19, 2017:28(1)), possibly because the omega-3 fatty acids in most fish help to reduce inflammation and clotting that increase heart attack risk.

My Recommendations
In the United States and many other parts of the world, cardiovascular disease is the leading cause of death and meat is a major risk factor. While the risk of developing cardiovascular disease (including heart attacks and strokes) increases with age, other risk factors are influenced by lifestyle at any age. Lifestyle and behaviors that are known to improve cardiovascular health include:
• eating healthful foods –fruits, vegetables, whole un-ground grains, beans and seeds
• exercising regularly
• getting sufficient sleep
• maintaining a healthy body weight
• stopping smoking
• restricting or avoiding alcohol
• controlling high blood pressure, high cholesterol and high blood sugar