Jane E. Persons, Jess G. Fiedorowicz, M.D., Ph.D.

Omega-3 fatty acids, particularly docosahexaenoic acid (DHA) and eicosahexaenoic acid (EPA), have been suggested to have a protective effect on mental health.  The United States Institute of Medicine recommends a daily combined intake of DHA and EPA of 100 mg (1); however, it has been suggested that a daily intake of 500 mg, and even up to 1,000mg, may be beneficial (2). Short of eating fish every day, is this level of intake even attainable without resorting to supplement use? The answer is not quite so simple, becoming less a matter of what food we eat, and more a matter of what we feed our food.
 
Aging mammals and birds have the ability to convert alpha-linolenic acid (ALA) into EPA and DHA.  Thus, animals who are provided a diet rich in omega-3 fatty acids in turn provide a rich source of omega-3’s when they themselves are consumed. In this age of factory farming, cattle are routinely fed a grain-based diet, allowing farmers to rapidly and inexpensively raise product for sale.  However, grain is deficient in omega-3 fatty acids and high in omega-6, which is in turn reflected in the meat and milk produced (3). A recent study out of Australia has shown that beef from exclusively grass-fed cattle provides 23 mg of DHA and 135 mg EPA per 4 oz serving of meat, compared to 20 mg of DHA and 72 mg EPA provided by grain-fed cattle (4). Game animals are also a good source of omega-3 fatty acids, due to their ALA-rich diet of ferns and other forest vegetation, as are the meat and eggs of pasture-raised poultry (3). Eggs from pasture-raised chickens contain 6.6 mg of DHA and 1.2 mg of EPA per gram of yolk, which figures to approximately 120 mg of DHA and 23 mg of EPA per large egg – more than six times the amount provided by the eggs of grain-fed chickens (5). Many of the same omega-3-rich wild plants consumed by animals as forage can also be eaten by humans. Purslane, an antioxidant-rich leafy green as frequently touted for its taste and nutritional value as it is cursed as a common weed, provides 22 mg of EPA per pound (3).
 
With careful consideration of not just the food we eat, but also what happens before food reaches our plate, it is possible to consume adequate amounts of DHA and EPA without supplement use.  Nutritionally, we can expect to obtain from a food only that which has been put in. By ensuring our livestock are properly nourished we can in turn ensure the same for ourselves, to the potential benefit of both our physical and our mental health. 

References
1.    Kris-Etherton PM, Grieger JA, Etherton TD. Dietary reference intakes for DHA and EPA. Prostaglandins, leukotrienes, and essential fatty acids. 2009;81(2-3):99-104.
2.    Harris WS, Mozaffarian D, Lefevre M, Toner CD, Colombo J, Cunnane SC, et al. Towards establishing dietary reference intakes for eicosapentaenoic and docosahexaenoic acids. The Journal of nutrition. 2009;139(4):804S-19S.
3.    Simopoulos AP. Omega-3 fatty acids and antioxidants in edible wild plants. Biological research. 2004;37(2):263-77.
4.    Ponnampalam EN, Mann NJ, Sinclair AJ. Effect of feeding systems on omega-3 fatty acids, conjugated linoleic acid and trans fatty acids in Australian beef cuts: potential impact on human health. Asia Pacific journal of clinical nutrition. 2006;15(1):21-9.
5.    Simopoulos AP. The Mediterranean diets: What is so special about the diet of Greece? The scientific evidence. The Journal of nutrition. 2001;131(11 Suppl):3065S-73S.