18:2 n-6 is linoleic acid (the short-chain omega-6)
18:3 n-3 is alpha-linolenic acid (the short-chain omega-3)
20:4 n-6 is arachidonic acid (the long-chain omega-6)
20:5 n-3 is EPA (eicosapentaenoic acid, a long-chain omega-3)
22:5 n-3 (DPA) (docosapentaenoic acid, a long-chain omega-3)
22:6 n-3 is DHA (docosahexaenoic acid,a long-chain omega-3)
But a free software program that Dr. Lands developed for the National Institutes of Health makes it easier for us to choose foods higher in omega-3 and lower in omega-6. It runs on either a PC or a Mac.
This program is KIM-2 (Keep in Managed, version 2), and it shows both short-chain and long-chain omega-3 and omega-6 content of more than 9,000 food servings. This is the same data that the U.S. Department of Agriculture's National Nutrient Database has, except that the USDA presents its data in grams and KIM-2 presents them in milligrams. KIM-2 is much easier to use than the USDA's tables once you download it at http://efaeducation.nih.gov/sig/kim.html and get the hang of it.
Still, KIM-2 can be frustrating, because its main menu is not intuitive. This program can do a lot, but I use it simply to find the omega-3 and omega-6 content of foods. To do that, from the main menu I go to "Recipes" button and from there click on "New choice," which brings up the entire list of foods. From there I can scroll through the list, but I usually click on the "Find a specific food" button.
I continue to be amazed at what I find when searching through the KIM-2 database! For example, let's consider tree nuts like walnuts and almonds and ground nuts like peanuts.
Walnuts have a positive reputation as being high in omega-3 fats. For example, a recent email newsletter from Dr. Andrew Weil says this: "A mainstay of Dr. Weil’s nutrition recommendations, walnuts are an excellent vegetarian source of omega-3 fatty acids, protective fats that promote cardiovascular health, cognitive function, and anti-inflammatory activity."
But the most common species of walnuts, often called the English walnut, has 45,712 mg of omega-6 in each cup of the chopped pieces and 10,986 mg of omega-3 (the other main type, black walnuts, has almost as much omega-6). This is indeed one of the highest levels of omega-3 of any nut, but the pro-inflammatory effect of its omega-6 content far outweighs that.
Learning about the omega-6 level in the ubiquitous peanut -- whether shelled, made into peanut butter, or into peanut oil -- was a great disappointment to Dr. Lands, he says. For example, one cup of raw Valencia peanuts has 21,431 mg of omega-6.
Among the tree nuts, the otherwise wonderful almond has 17,344 mg of omega-6 in each cup. One cup of raw macadamias has 1,737 mg, making it the best of the nuts in terms of omega-6, although three little-known seeds actually have more omega-3 than omega-6 (watch for a forthcoming article here).
My conclusion is that the easiest way to cut back on our omega-6 intake is to focus on those foods that we eat a lot and also have a lot of omega-6, even if they also have a decent amount of omega-3. For most of us this means avoiding the four most common cooking oils as well as most nuts and seeds.