It has been a good 25 years in the making, but there is now consensus that omega-3 fatty acids are beneficial to health and that most Americans do not consume enough of them.
In fact, the United States is among the countries with the world’s lowest consumption of these polyunsaturated fatty acids (PUFAs). The U.S. Dept. of Agriculture estimates intakes of about 100 mg/day, whereas five times that amount is recommended for cardiovascular health. The American Heart Association recommends consumption of at least two meals of fatty fish per week for people without heart disease, and 1 g/day of long-chain omega-3s, mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), for those with the disease. The International Society for the Study of Fatty Acids and Lipids recommends an intake of 500 mg of EPA and DHA per day.
Meeting these recommendations means a sea change in food habits. Exacerbating the low intake of omega-3 PUFAs is the high consumption of the omega-6 PUFA linoleic acid, the predominant PUFA in soybean and canola oils. Intake of linoleic acid is 10 times that of all omega-3s, and in some people 25 times greater. Omega-6 and omega-3 fatty acids share the same metabolic enzymes and generally have opposing biological effects. With such an imbalanced intake of these two PUFA classes, the effects of linoleic acid predominate. In excess amounts, omega-6 PUFAs are pro-inflammatory and pro-thrombotic and may be pro-carcinogenic.
Boosting omega-3 intakes emphasizes fatty fish because these fish contain the greatest amounts of EPA and DHA. These long-chain forms are the most potent and effective omega-3 PUFAs in all health conditions examined so far. Yet fish consumption in the U.S. is the lowest of all animal proteins, less than half that of beef or poultry, with many people consuming virtually no fish. Long-chain omega-3s occur in few other foods than fish, the exceptions being some omega-3-enriched eggs and trace amounts in poultry fed fish meal.
Despite myriad health benefits associated with eating fish and long-chain omega-3s—including fetal and infant neurodevelopment, cardiovascular health, immune and inflammatory function, visual function, mental health, and several clinical conditions—some groups continue to spread alarm about the dangers of eating fish. Yes, some fish carry undesirable levels of contaminants, the most dangerous of which is methylmercury. The Food and Drug Administration has identified these species and issued science-based guidance for safe fish consumption targeted to those people at greatest risk from methylmercury—pregnant women and young children.
Health risks from eating contaminated fish have, in my view, been greatly exaggerated by fearmongers for reasons unrelated to health and science. Unless one consumes large amounts of contaminated fish frequently (and some groups do), most people put their health at greater risk by not eating seafood than from eating different types of fish regularly—at least twice a week. The health benefits of eating fish far outweigh the risks.
One often hears that if you don’t like fish or fear contaminants, just eat the plant-based omega-3, better known as alpha-linolenic acid. This 18-carbon omega-3 PUFA is found in the oils of flax, perilla, hempseed, canola, wheat germ, walnuts, soybean, and chia. Humans can convert alpha-linolenic acid to EPA and DHA, but they do so very inefficiently. Recent studies indicate that less than 5% is converted to long-chain forms. Some 60% or more of dietary alpha-linolenic acid is oxidized, some is converted to other fatty acids and cholesterol, and a small fraction goes to the long-chain forms. Moreover, conversion is inhibited by high intakes of linoleic acid, alpha-linolenic acid, and long-chain omega-3s. Relying solely on alpha-linolenic acid for DHA needed during pregnancy and lactation for fetal and infant neurodevelopment is unlikely to meet the growing brain’s need for DHA.
But alpha-linolenic acid has many favorable features. It has several cardiovascular benefits, although they are less potent than those of EPA and DHA. It may also be protective in other clinical conditions, but evidence is too scarce to be conclusive. In brain, it is a substrate for cholesterol synthesis, an important structural lipid. Foods rich in alpha-linolenic acid can help offset the excessively high intakes of linoleic acid that characterize American food habits, helping to redress the imbalanced intake of these two fatty acid classes.
Increased demand for omega-3 PUFAs for consumer consumption, food fortification, new products, and dietary supplements is unlikely to be met from fish because of sharply declining fish populations, overfishing, and the relatively few alternative food sources of these fatty acids. Rapid advances in plant biotechnology, however, have resulted in soybean and canola modified to contain stearidonic acid, the first intermediate in the conversion of alpha-linolenic acid to long-chain forms. Stearidonic acid is rapidly converted to EPA but not DHA in humans.
Within the past few months, two independent teams of researchers have demonstrated that plants transformed with multiple genes from nonmammalian organisms can synthesize DHA. These reports herald the development of commercial oilseed crops able, one day, to provide abundant quantities of omega-3 PUFAs for new food uses. In the meantime, it behooves all of us to boost our intake of omega-3s, especially the long-chain forms.