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2009-07-24 03:35:25
A high intake of polyunsaturated fat in the diet, while good for the heart, may
lead to inflammatory bowel disease, say researchers.
Experts believe a high intake of linoleic acid, found in foods like "healthy"
margarines, may be implicated in a third of ulcerative colitis cases.
The researchers base their findings, due to be published in Gut, on food
diaries from more than 200,000 people.
If the link proves to be causal, some people might want to modify their diet.
There is good biological plausibility of why linoleic acid can cause
inflamation, and certainly Western diets are often excessive in this kind of
fat
Dr Anton Emmanual Core
The researchers also found that a diet rich in another type of fat, omega 3
fatty acid found in oily fish such as salmon and herring, reduced the
likelihood of developing ulcerative colitis by 77%.
Linoleic acid is a naturally occurring essential fatty acid, present in a
variety of foods, including the oils of seeds and nuts, such as sunflower,
safflower, soya, corn seeds or walnut oils.
The multinational team working on the EPIC (European Prospective Investigation
into Cancer and Nutrition) study say there is a plausible biological mechanism
that could explain why linoleic acid is linked with this bowel condition.
Cell membranes
Once in the body, linoleic acid is converted to arachidonic acid, which is a
component of the cell membranes in the bowel.
Arachidonic acid can then be converted into various inflammatory chemicals,
high levels of which have been found in the bowel tissue of patients with
ulcerative colitis.
In all, 126 of the people in the study developed ulcerative colitis after an
average period of four years.
After adjusting for other factors likely to influence the results, including
smoking, age, total energy intake, and use of aspirin, those whose diets
included the most linoleic acid were more than twice as likely to develop the
condition as those whose diets contained the least.
Lead researcher Dr Andrew Hart of the University of East Anglia, Norwich, said:
"There are no dietary modifications of benefit in patients with ulcerative
colitis, although, based on this study's findings, a diet low in linoleic acid
may merit investigation."
In the UK, people consume on average about 10g per day of linoleic acid, found
in around nine level teaspoons of polyunsaturated margarine or three teaspoons
of sunflower oil.
In the study, the people who consumed the most linoleic acid had a daily intake
three times this or more.
Biologically plausible
Dr Anton Emmanual, medical director of the digestive disorders charity Core,
stressed that the study did not prove that linoleic acid caused bowel
disorders, and warned that dietary diaries could be unreliable.
However, he said: "Nevertheless there is good biological plausibility of why
linoleic acid can cause inflamation, and certainly Western diets are often
excessive in this kind of fat.
"The omega 3 fish oils counteract the harmful effects of lineloic acid it would
be helpful to see whether diets high in fish oils reduce colitis.
"Lineloic acid may have small part to play in some patients, but factors such
as smoking, bacteria and stress are likely to be at least as important."
Professor Jon Rhodes, of the British Society of Gastroenterology, said the
study was interesting, but also stressed it did not prove cause and effect -
further tightly controlled studies would be needed to do that.
Dr Elisabeth Weichselbaum, of the British Nutrition Foundation, said the study
was interesting.
But added: "The results need to be interpreted with caution.
"People who have very high intakes of omega-6 fats are likely to have a
generally different diet from those with low intakes. Therefore, it may as well
be possible that there are other factors that could have an effect."