(CBS NEWS) -- The link between red meat and heart disease risk is nothing new, but a
new study shows the reason behind the risk may not be what doctors have
Researchers from the Cleveland Clinic have
discovered it's not the saturated fats or cholesterol from a fatty steak
that's triggering heart problems, but a chemical process involving gut
bacteria and a compound found in meat called carnitine that may be to
"Carnitine metabolism suggests a new way to help explain
why a diet rich in red meat promotes atherosclerosis," study author Dr.
Stanley Hazen, section head of preventive cardiology and rehabilitation
in the Miller Family Heart and Vascular Institute at the Cleveland
Clinic, said in a written statement.
is a disease of the arteries where plaque builds up, preventing
oxygen-rich blood from flowing to organs and other parts of the body.
This could lead to heart attacks, strokes and death.
his team were looking to build on previous research linking frequent red
meat consumption to increased rates of heart disease. Several of the
studies suggested that the fatty composition of meat alone accounted for
only a portion of the risk increase, according to Hazen, with meat's
salt content, genetic risk factors or something about cooking itself
possibly accounting for the remaining risk.
According to the researchers, an earlier study found that a compound
called trimethylamine-N-oxide (TMAO) may promote the growth of
artery-clogging plaques. TMAO is formed when bacteria from our digestive
tract breaks down a compound found in meat known as carnitine. Diets
high in meat promote the growth of a gut bacteria that breaks down
carnitine, the researchers explained, which leads to more TMAO, which in
turn leads to atherosclerosis. The study authors set out to learn more
about how this process affects heart risks, by comparing the carnitine
and TMAO levels found among meat-eaters, vegans and vegetarians.
evaluated 2,595 patients undergoing heart exams, and found increasing
carnitine levels increased risks for stroke, heart attacks and other
cardiac events in subjects with high levels of TMAO. Vegans and
vegetarians had significantly lower baseline levels of TMAO than
meat-eating omnivores, the researchers found. Vegetarians and vegans
given carnitine did not show major increases in TMAO levels, however,
when compare with meat-eaters who consumed the same amount of carnitine,
which suggests vegetarians may possess different gut bacteria.
One vegan even agreed to eat a 200-gram sirloin steak to see how carnitine and TMAO levels would be affected, Nature News reported.
bacteria living in our digestive tracts are dictated by our long-term
dietary patterns," said Hazen. "A diet high in carnitine actually shifts
our gut microbe composition to those that like carnitine, making meat
eaters even more susceptible to forming TMAO and its artery-clogging
effects. Meanwhile, vegans and vegetarians have a significantly reduced
capacity to synthesize TMAO from carnitine, which may explain the
cardiovascular health benefits of these diets."
also looked at the effects of a diet heavy in carnitine by testing
normal mice and mice with suppressed levels of gut bacteria, and
concluded that TMAO prevents the breakdown of cholesterol, thereby
raising risk for atherosclerosis.
Hazen noted that besides being
found in red meats, carnitine is also added to dietary supplements to
boost weight loss, and is commonly found in another item linked to heart
risks -- energy drinks.
"We need to examine the safety of
chronically consuming carnitine supplements as we've shown that, under
some conditions, it can foster the growth of bacteria that produce TMAO
and potentially clog arteries," he said.
The study was published April 7 in Nature Medicine.
really a beautiful combination of mouse studies and human studies to
tell a story I find quite plausible," Dr. Daniel J. Rader, a heart
disease researcher at the University of Pennsylvania School of Medicine,
who was not involved in the study, told The New York Times.
Dr. Harlan Krumholtz, professor of medicine and epidemiology and public health at Yale University School of Medicine, wrote for Forbes
that the study may be potentially groundbreaking, but the findings to
be repeated before doctors start measuring people's gut bacteria to
determine their disease risk from eating meat.
"This study needs
to be replicated by others and we need to determine how such knowledge
may be translated into action that might actually help people," he wrote
"The study starts with the presumption that red meat causes heart
disease, but the medical literature is actually has a lot of conflicting
information," Krumholtz, who was not involved in the research, also
One expert not involved in the research said people may still be able to eat meat occasionally without risk.
no need to change our dietary recommendations from this," Catherine
Collins, a dietitian at the U.K. nonprofit Science Media Centre, told Business Insider.
"A Mediterranean style diet with modest meat, fish, dairy and alcohol
intake, coupled with more pulses, vegetables fruits, whole grains and
mono-unsaturated fats, remains the nutritional blueprint for a healthy
and healthful life."