A fish - oil - story.

A fish (oil) story?

While epidemiologic research suggests that diets high in fishoil protect against heart disease, researchers have not yet determined how best to incorporate the substance into a Western diet, says Garret A. FitzGerald of Vanderbilt University in Nashville. Until that time, he says, eating more fish is fine but taking fish oil supplements may not be such a good idea.

The original studies linking fish oil consumption to a lowerrisk of heart disease were done more than a decade ago by Danish researchers, who found that Eskimos had a far lower incidence of heart disease than Danes, but that the Eskimos' risk went up if they moved to Denmark. On the basis of their knowledge of metabolic pathways involving the conversion of fats to substances that either harm or help the cardiovascular system, the Danes concluded that a particular type of oil in the Eskimo diet could be the protective factor. They sent samples of Eskimo food, including seal meat and fish, back to Denmark for analysis. By determining how much oil was in the samples, they were able to estimate the amount in the average Eskimo diet. But, says FitzGerald, they had neglected to freeze the samples before shipping. Years later, they repeated the study but froze the samples for shipping and came up with an average fish oil consumption about three times their original estimates.

Companies marketing fish oil have based the amount ofactive ingredients in their capsules on the original study, FitzGerald says. Even if the epidemiologic evidence were strong enough to recommend fish oil supplementation -- and FitzGerald says that on its own, it isn't -- he estimates that according to the later study, people would have to swallow an average of 50 capsules a day. this, says FitzGerald, "defies logic and the gastrointestinal properties of most volunteers."

While advances are being made in understanding the activeingredients in fish oil (SN: 5/11/85, p.295; 10/19/85, p.252), the value of supplements in preventing cardiovascular disease has not yet been proved. There have been at least two cases of people on the capsules suffering a precipitous decline in the level of platelets, a blood component involved in clotting. This side effect, says FitzGerald, "is rare but disturbing."

"If there is a beneficial effect, then it's likely to be a modestone compared to risk factors we're familiar with," he says.