How red meat may increase heart attack risk

How Red Meat May Increase Heart Attack Risk
March 01, 2015
 by Gabe Mirkin, MD

This month, the 2015 Dietary Guidelines Advisory
Committee 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,
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.

 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
 • Mice given antibiotics to prevent this
bacterial overgrowth in the gut do not develop
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.