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zoom RSS 赤身の肉の成分による心臓障害

<<   作成日時 : 2013/04/10 23:46   >>

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赤身の肉に含まれるカルニチンの分解産物が心臓障害をもたらす。
 赤身の肉に含まれる化学物質が多量のステーキやミンチ・ベーコンが心臓に悪い理由を説明するのに役立つ。
 英国では赤身肉・加工肉は1日70g、ベーコンは2切れ以上を食べないよう推奨している。飽和脂肪や加工肉の保存料が心臓障害に影響すると考えられてきたが、それは一部に過ぎない。
 マウスやヒトの実験で、腸内細菌がカルニチンを分解し、肝臓でTMAOと呼ばれる化学物質に変換される。TMAOはコレステロール代謝に影響し、コレステロールの蓄積につながっている。
 菜食主義者はカルニチン分解細菌の数が少ないという。

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8 April 2013 Last updated at 00:08 GMT
Red meat chemical 'damages heart', say US scientists
By James Gallagher
Health and science reporter, BBC News
http://www.bbc.co.uk/news/health-22042995

画像A chemical found in red meat helps explain why eating too much steak, mince and bacon is bad for the heart, say US scientists.

A study in the journal Nature Medicine showed that carnitine in red meat was broken down by bacteria in the gut.

This kicked off a chain of events that resulted in higher levels of cholesterol and an increased risk of heart disease.

Dieticians warned there may be a risk to people taking carnitine supplements.

There has been a wealth of studies suggesting that regularly eating red meat may be damaging to health.

In the UK, the government recommends eating no more than 70g of red or processed meat a day - the equivalent of two slices of bacon.

Saturated fat and the way processed meat is preserved are thought to contribute to heart problems. However, this was not thought to be the whole story.


"The cholesterol and saturated fat content of lean red meat is not that high, there's something else contributing to increases in cardiovascular risk," lead researcher Dr Stanley Hazen told the BBC.

Gut bugs
Experiments on mice and people showed that bacteria in the gut could eat carnitine.

Carnitine was broken down into a gas, which was converted in the liver to a chemical called TMAO.

In the study, TMAO was strongly linked with the build-up of fatty deposits in blood vessels, which can lead to heart disease and death.

Dr Hazen, from the Cleveland Clinic, said TMAO was often ignored: "It may be a waste product but it is significantly influencing cholesterol metabolism and the net effect leads to an accumulation of cholesterol.

"The findings support the idea that less red meat is better.

"I used to have red meat five days out of seven, now I have cut it way back to less than once every two weeks or so."

He said the findings raised the idea of using a probiotic yogurt to change the balance of bacteria in the gut.

Reducing the number of bacteria that feed on carnitine would in theory reduce the health risks of red meat.

Vegetarians naturally have fewer bacteria which are able to break down carnitine than meat-eaters.

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Nat Med. 2013 Apr 7. doi: 10.1038/nm.3145. [Epub ahead of print]

Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis.

Koeth RA, Wang Z, Levison BS, Buffa JA, Org E, Sheehy BT, Britt EB, Fu X, Wu Y, Li L, Smith JD, Didonato JA, Chen J, Li H, Wu GD, Lewis JD, Warrier M, Brown JM, Krauss RM, Tang WH, Bushman FD, Lusis AJ, Hazen SL.

1] Department of Cellular & Molecular Medicine, Cleveland Clinic, Cleveland, Ohio, USA. [2] Center for Cardiovascular Diagnostics & Prevention, Cleveland Clinic, Cleveland, Ohio, USA.

Abstract
Intestinal microbiota metabolism of choline and phosphatidylcholine produces trimethylamine (TMA), which is further metabolized to a proatherogenic species, trimethylamine-N-oxide (TMAO). We demonstrate here that metabolism by intestinal microbiota of dietary l-carnitine, a trimethylamine abundant in red meat, also produces TMAO and accelerates atherosclerosis in mice. Omnivorous human subjects produced more TMAO than did vegans or vegetarians following ingestion of l-carnitine through a microbiota-dependent mechanism. The presence of specific bacterial taxa in human feces was associated with both plasma TMAO concentration and dietary status. Plasma l-carnitine levels in subjects undergoing cardiac evaluation (n = 2,595) predicted increased risks for both prevalent cardiovascular disease (CVD) and incident major adverse cardiac events (myocardial infarction, stroke or death), but only among subjects with concurrently high TMAO levels. Chronic dietary l-carnitine supplementation in mice altered cecal microbial composition, markedly enhanced synthesis of TMA and TMAO, and increased atherosclerosis, but this did not occur if intestinal microbiota was concurrently suppressed. In mice with an intact intestinal microbiota, dietary supplementation with TMAO or either carnitine or choline reduced in vivo reverse cholesterol transport. Intestinal microbiota may thus contribute to the well-established link between high levels of red meat consumption and CVD risk.
PMID: 23563705

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