Studies compare impacts of dietary red meat versus other protein sources.

Heart disease is the leading cause of death for both men and women in the United States and every year about 610,000 people die of heart disease, for one in every four deaths. Statistics from the Cayman Islands Economics & Statistics Office have revealed that diseases of the circulatory system are the leading causes of death in Cayman Islands.

In concurrent studies, Cleveland Clinic researchers have uncovered new mechanisms that demonstrate why and how regularly eating red meat can increase the risk of heart disease, and the role gut bacteria play in that process.

The research, led by Stanley Hazen, M.D., Ph.D., builds upon previous work showing TMAO (trimethylamine N-oxide) – a gut bacteria byproduct formed during digestion – can lead to the development of cardiovascular disease, including heart attacks and strokes. TMAO is produced when gut bacteria digest choline, lecithin and carnitine, nutrients that are abundant in animal products such as red meat and liver and other animal products.

In a new dietary intervention study published in the European Heart Journal, the researchers found that a diet rich in red meat as the primary protein source significantly increases circulating TMAO levels, compared to diets with white meat or non-meat as protein sources. The study showed chronic red meat consumption enhanced the production of TMAO by gut microbes and reduced the kidneys’ efficiency of expelling it. Both enhanced production and reduced elimination caused by a red meat diet contribute to elevation in TMAO levels, which has been linked to the development of atherosclerosis and heart disease complications.

High levels of TMAO in the blood have been shown to be a powerful tool for predicting future heart attack, stroke and death risks, according to previous research initially spearheaded by Dr. Hazen and his team, and subsequently replicated around the world. TMAO testing is now in clinical use as a result. Dr. Hazen chairs the Department of Cellular and Molecular Medicine in Cleveland Clinic’s Lerner Research Institute and is co-section head of Preventive Cardiology & Cardiac Rehabilitation in the Miller Heart &Vascular Institute.

The study included 113 participants who sequentially (in random order) were provided complete meal plans prepared using either red meat, white meat or non-meat (mostly vegetarian) protein sources as 25 percent of their daily calories. All participants had a wash-out diet in between meal plans.

After one month of the red meat diet, the vast majority of study participants experienced an elevation in TMAO levels in blood and urine. On average, TMAO levels in the blood increased approximately 3-fold during the red meat diet, compared to the white meat or non-meat diets, with some patients showing over a 10-fold rise. Similar increases were observed in the urine. However, after patients stopped the red meat diet, TMAO levels in the blood and urine subsided over the following month.

The study also revealed the unanticipated finding that a participant’s chronic dietary choices impacted kidney function by changing the effectiveness of the kidneys to expel compounds. For example, while a red meat diet decreased TMAO excretion, the red meat diet increased the excretion efficiency of carnitine and other carnitine-derived metabolites.

“This is the first study of our knowledge to show that the kidneys can change how effectively they expel different compounds depending on the diet that one eats – other than salts and water,” said Dr. Hazen, who also directs Cleveland Clinic Center for Microbiome and Human Health. “We know lifestyle factors are critical for cardiovascular health, and these findings build upon our previous research on TMAO’s link with heart disease. They provide further evidence for how dietary interventions may be an effective treatment strategy to reduce TMAO levels and lower subsequent risk of heart disease.”

About Cleveland Clinic

Cleveland Clinic is a nonprofit multispecialty academic medical center that integrates clinical and hospital care with research and education. Located in Cleveland, Ohio, it was founded in 1921 by four renowned physicians with a vision of providing outstanding patient care based upon the principles of cooperation, compassion and innovation. Cleveland Clinic has pioneered many medical breakthroughs, including coronary artery bypass surgery and the first face transplant in the United States. U.S. News & World Report consistently names Cleveland Clinic as one of the nation’s best hospitals in its annual “America’s Best Hospitals” survey.

Among Cleveland Clinic’s 52,000 employees are more than 3,600 full-time salaried physicians and researchers and 14,000 nurses, representing 140 medical specialties and subspecialties. Cleveland Clinic’s health system includes a 165-acre main campus near downtown Cleveland, 11 regional hospitals, more than 150 northern Ohio outpatient locations – including 18 full-service family health centers and three health and wellness centers – and locations in Weston, Fla.; Las Vegas, Nev.; Toronto, Canada; Abu Dhabi, UAE; and London, England. In 2017, there were 7.6 million outpatient visits, 229,000 hospital admissions and 207,000 surgical cases throughout Cleveland Clinic’s health system. Patients came for treatment from every state and 185 countries. Visit us at clevelandclinic.org. Follow us at twitter.com/ClevelandClinic. News and resources available at newsroom.clevelandclinic.org.