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More diet 'wisdom' questioned.

My father, who died peacefully in his late eighties, ignored recommendations to avoid eating saturated fat, saying that he had eaten butter all his life and it had never done him any harm. It seems he may have been right.

This week's BMJ has a research paper and accompanying editorial questioning the American Heart Association's advice on diet to prevent heart disease. The Association recently repeated its advice to maintain and even increase your intake of linoleic acid, which is found in high concentration in vegetable oils such as corn, sunflower, safflower, and soybean oils. We are supposed to use these oils in preference to saturated fat.

There is little objective evidence to show that exchanging linoleic acid for saturated fat does any good. Most trials of this hypothesis have involved other dietary changes and/or other interventions. And the new research suggests that increasing linoleic acid may actually be bad for you.

The researchers, Ramsden and colleages, looked at the original data from the Sydney Diet Heart Study, a randomised controlled trial conducted between 1966 and 1977 and involving 458 men aged 30 to 59 who had had a recent coronary event. Total serum cholesterol was lowered in those taking an increased amount of linoleic acid but deaths from heart disease were not reported in the original paper.

The new research is based on a re-examination of the original data (a technically difficult task). They found that mortality due to heart disease was higher in the group taking increased linoleic acid. Notice that this happend even though the serum cholesterol level in these men was reduced.

These findings contradict the view that replacing saturated fat with linoleic acid is a good idea. They do agree with what Gary Taubes contends in The Diet Delusion, in which he claims that saturated fat is not harmful.

What strikes me particularly about this is that the original researchers assumed unquestioningly that reducing serum cholesterol would automatically lead to a reduction in deaths from coronary heart disease. It didn't, and in fact their intervention actually increased the death rate from this cause.


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