Tuesday, November 14, 2006 - 1:35 PM

Omega-3 and Omega-6 Polyunsaturated Fatty Acids in the American Diet.

Joyce A. Nettleton, ScienceVoice Consulting, 2931 Race St., Denver, CO 80205

Omega-3 polyunsaturated fatty acids (PUFAs) have given fats a good image, but can they deliver their potential health benefits in American diets? American adults consume 33% of their energy from fat, two-thirds of which comes from saturated and monounsaturated fatty acids. PUFA intake is mainly linoleic acid, an omega-6 PUFA predominant in soybean, corn, sunflower and safflower oils. Linoleic acid intake (13.8 g/day) exceeds that of alpha-linolenic acid (ALA), a plant-based omega-3 PUFA, by 10 times (1.4 g/day), and in some diets may be as great as 20-25 times greater. Neither linoleic acid or ALA can be synthesized de novo by humans, nor can they be interconverted. Because they are essential for growth and maintenance, they must be obtained from the diet. Primary food sources of linoleic acid and ALA in the U.S. are soybean and canola oils. Extensive health benefits have been associated with omega-3 PUFAs, mainly the long-chain forms eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found almost exclusively in fish and shellfish. However, similar health benefits in some conditions have been reported with increased ALA consumption, but data are more limited. ALA can be converted to the long-chain forms, but very inefficiently in humans. Limitations on ALA conversion to EPA and the potential benefits from stearidonic acid, an intermediate in the conversion process, will be discussed. Other questions considered will be: whether the need for DHA in pregnancy to provide for fetal development can be met in vegetarian diets or mainly from ALA, in current American diets; the addition of omega-3 PUFAs to various foods and their marketing; implications of current PUFA consumption patterns; and recommended PUFA intakes.