Polyunsaturated Fat May Protect Against Stroke

Source: Tufts University
September 18, 2002 (Reviewed: September 3, 2004)

Diet likely plays an active role in mediating stroke risk, but scientists continue to work on the details of how different types of dietary fats help or hurt blood vessels, including those that supply blood to the brain. More information has come from a recent study published in Stroke that associates high blood levels of a polyunsaturated fatty acid with a reduced risk of ischemic stroke.

The study

For this analysis, Japanese researchers identified 197 participants of a cardiovascular risk study who had suffered a stroke at some point during the study. They then recruited another 591 healthy participants, matched for gender, age, and community, to serve as controls. Blood samples collected during the study were used to assess fatty acid profiles. The outcome of interest was the incidence of the most common form of stroke - ischemic (i.e. thrombotic, embolic, or lacunar).

The researchers found that, after controlling for multiple confounders, including cardiovascular risk factors, the presence of diabetes, and levels of other fatty acids, a high serum level of linoleic acid, a polyunsaturated fat found in vegetable oils, was associated with a significantly reduced risk of ischemic stroke - odds ratios of approximately 0.65 for a 1-standard deviation increase in the linoleic acid level. Serum levels of saturated fatty acids and monounsaturated fatty acids were not associated with an increased risk of stroke.

Surprisingly, omega-3 fatty acids -- the "heart-healthy" type of fat commonly found in fatty varieties of fish -- did not have an impact on stroke risk in this study. The authors speculate that, since Japanese consumers typically eat a lot of fish, everyone in the study was already getting the benefits of an omega-3-rich diet. On the other hand, studies done in Western countries where people typically eat less fish have shown a link between omega-3s and a reduced chance of stroke.

Proposed pathways

The scientists offer several possible explanations for their findings. Linoleic acid reduces platelet aggregation and enhances erythrocyte deformation; the authors point out that both promote adequate circulation in small blood vessels, which would the lower risk of lacunar infarct. There is also some evidence that linoleic acid may help lower cholesterol levels, moderate blood glucose levels, and regulate blood pressure, all of which would make a stroke less likely.

Advice to patients

The authors of this study emphasize that strokes result from many factors, and it is too early to tell to what degree diet was responsible for the results seen in this study. But they are encouraged by the fact that high blood levels of a fatty acid found in vegetable oil seemed to substantially reduce ischemic stroke risk in this population.

In fact, heart-health nutrition guidelines already encourage a diet that emphasizes the polyunsaturated fats in vegetable oils and limits foods high in saturated fats. Food manufacturers undo some of the health benefits of polyunsaturated fats when they hydrogenate them to make solid margarine and shortening, thereby increasing the products' trans fat content. Consumers are better off using vegetable oils in their natural, liquid state. If they do use margarine, encourage them to choose liquid or soft varieties.

Source

• Linoleic acid, other fatty acids, and the risk of stroke. H. Iso, S. Shinichi, U. Umemura,  et al., Stroke, 2002, vol. 33, pp. 2086--2093

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