A new study shows that people who eat a lot of red meat are more susceptible to heart problems — but the fat in the meat might have little to do with it.
Dr. Stanley Hazen of the Cleveland Clinic, a nonprofit academic medical center, and his colleagues have accumulated evidence for a surprising new explanation of why red meat might contribute to heart disease.
Researchers say that what damages hearts is not just the thick edge of fat on steaks. The real culprit, they propose, is a little-studied chemical that is burped out by bacteria in the stomach after people eat red meat. It is converted by the liver into yet another little-studied chemical called TMAO that gets into the blood and increases the risk of heart disease.
The researchers also found that TMAO caused heart disease in mice. Studies with 23 vegetarians and vegans and 51 meat-eaters showed that meat-eaters normally had more TMAO in their blood and they, unlike those who spurned meat, readily made TMAO after swallowing pills with the chemical transformed by the bacteria, carnitine.
The investigators’ extensive experiments in both humans and animals, published Sunday in Nature Medicine, have persuaded scientists not connected with the study to seriously consider this new theory of why red meat eaten too often might be bad for people.
“It’s really a beautiful combination of mouse studies and human studies to tell a story I find quite plausible,” said Dr. Daniel J. Rader, a heart-disease researcher at the University of Pennsylvania School of Medicine, who was not involved in the research.
Researchers say the work could lead to new treatments for heart disease and also to a new way to assess heart disease risk by looking for TMAO in the blood.
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.
Hazen said he worries about carnitine-containing energy drinks. Carnitine often is added to the drinks on the assumption that is will speed fat metabolism and increase a person’s energy level, he said.
