BATON ROUGE, LOUISIANA. Unsaturated fatty acids from oils found in fish (eicosapentaenoic acid and docosahexaenoic acid) are highly effective in preventing death from cardiovascular disease. Fish oils have strong antiarrhythmic properties and help prevent death from ventricular fibrillation; they also help prevent blood clotting and lower cholesterol and triglyceride levels.
Oils from fish (n-3 polyunsaturated fatty acids) and n-6 polyunsaturated fatty acids (from vegetable oils) are metabolized in a similar way and n-3 polyunsaturated fatty acids (n-3 PUFAs) have been shown to block the conversion of linoleic acid, the major n-6 PUFA in vegetable oils, to arachidonic acid. These interactions and competitive metabolic pathways have raised concerns that the benefits of fish oil consumption may be reduced if the diet is high in n-6 PUFAs from vegetable oils.
Researchers at the Louisiana State University have just released the results of a major study aimed at addressing these concerns. Their study involved 68 healthy men and women between the ages of 18 and 49 years. The participants consumed diets containing varying amounts of fish and vegetable oils for an eight-week period. The researchers found that fish oil supplementation lowered the blood plasma levels of triglycerides and arachidonic acid independent of the level of n-6 PUFAs in the diet. They conclude that vegetable oil in the diet does not reduce the benefits of fish oil in lowering the risk of death from heart disease. They also conclude that the fish oil intake required to effectively reduce triglyceride levels is less than six grams/day and that higher intakes do not confer added benefits. The daily intake required to affect a meaningful reduction in fibrinogen concentration (an indicator of blood clotting tendency) is less clear; it may be as low as 1.3 grams/day or as high as 15 grams/day. Further work is required to settle this question. [30 references]
Hwang, Daniel H., et al. Does vegetable oil attenuate the beneficial effects of fish oil in reducing risk factors for cardiovascular disease? American Journal of Clinical Nutrition, Vol. 66, July 1997, pp. 89-96
Connor, William E. Do the n-3 fatty acids from fish prevent deaths from cardiovascular disease? American Journal of Clinical Nutrition, Vol. 66, July 1997, pp. 188-89 (editorial)