A study carried out by researchers from Cleveland Clinic in
Ohio, US, has found that the chemical L-carnitine can increase the risk of
suffering from heart problems. Saturated fat and the manufacturing process
involved with how meat is preserved are widely believed to be related to heart
problems, but many health experts think there is more to it.
Lead researcher of the new study, Dr Stanley Hazen,
commented: “The cholesterol and saturated fat content of lean red meat is not
that high, there’s something else contributing to increases in cardiovascular
risk.”
L-carnitine is a nutrient which is contained in red meat,
dairy products and some dietary supplements.
The study, published in the journal Nature
Medicine, showed that the carnitine contained red meat was broken down by naturally
occurring bacteria in the gut.
However, this later resulted in higher levels of cholesterol
and an increased risk of heart disease as the resulting broken down product -
trimethylamine-N-oxide (TMAO), is known to speed up the build-up of plaque in arteries
and cause them to harden (atherosclerosis) – a main cause of heart disease.
Part of the researchers’ investigations was conducted in
humans, whilst other testing was carried out with mice. Studies involving
animals can be sometimes difficult to interpret, and some degree of caution
should be shown when generalising the findings to humans.
For the study, 77 healthy volunteers were administered a
supplement of L-carnitine. Of this total, 26 were classified as vegans or
vegetarians. Some of the meat-eaters in the group were told to eat an
eight-ounce sirloin steak - this works out at around 180mg of L-carnitine.
Researchers then gave antibiotics to the participants for a
one week period. These prevented bacteria in their gut from converting
L-carnitine into TMAO. After this, the 77 people again were given L-carnitine. Tests
were conducted on blood and urine at the beginning of the study and up to three
weeks following L-carnitine being given. Some of the people also had their
faeces analysed.
In addition, L-carnitine levels were checked in the blood of
2,595 other people, all of whom had attended a heart check-up. The researchers
thought this would be an effective measure of assessing a potential link with L-carnitine
levels and known cardiovascular disease, or risk of a cardiovascular event (i.e.
a heart attack or stroke).
Finally, plaque levels were studied in the arteries of mice
and this was done by comparing mice fed normally against a group of mice fed L-carnitine,
for a 10 week period. Some of these mice were given antibiotics beforehand.
The main findings
were:
. Meat-eaters
produced more TMAO compared to vegans or vegetarians following L-carnitine
ingestion.
. A ‘significant’
link was found between L-carnitine concentrations and risk of cardiovascular
event in those having heart check-ups. However this was only for those with a
high TMAO concentration. Researchers state they believe this shows that TMAO,
rather than L-carnitine, is the main factor of this link.
. A study of the
faeces showed L-carnitine affected how much TMAO was in the blood.
. Mice given
L-carnitine, were at a double risk of developing a plaque build-up in their
arterial walls, - but only when they had their normal gut bacteria. When the
animals were given antibiotics to clear the gut, L-carnitine did not cause the
same arterial wall build-up.
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