Dr. Lands replied that, "It is true. The accumulation of n-3 [omega-3] HUFA [highly unsaturated fatty acid] in tissues from dietary n-3 PUFA [polyunsaturated fatty acid] is higher when competition by dietary n-6 [omega-6] PUFA is lower."
In other words, until we reduce the amount of omega-6 in our systems, the omega-3 fats that we get from vegetarian sources contribute essentially nothing to balancing the effect of omega-6 fats with which they are in competition.
How, then, do we best cut back on omega-6? And what do we cut back on?
The absolute amount of omega-6 fatty acids in the individual foods that we eat is more important that the ratio of omega-6 to omega-3, even though almost all Americans need to bring the overall ratio way down. In other words, we don't have to stop eating otherwise healthful foods that are high in omega-6.
Let me give an example. One California avocado has 3,323 mg of pro-inflammatory short-chain omega-6 (linoleic acid) and just 199 mg of anti-inflammatory short-chain omega-3 (alpha-linolenic acid). But it also has lots of healthy monounsaturated fats, so avocados remain a staple of my diet.
What we do have to eliminate as much as possible are those foods that are sky-high in omega-6 that don't give us much in return. The first to go need to be the most common cooking oils, none of which has any redeeming value.
Soybean oil is the dominant one, followed by corn oil, canola oil, and cottonseed oil. These four make up 96 percent of all the vegetable oil sold in this country, according to Evelyn Tribole in her book The Ultimate Omega-3 Diet (McGraw Hill, 2007, pp. 28-29). In addition to cooking with them, manufacturers use them to make margarine, shortening, and salad dressings.
But just one tablespoon of soybean oil has 6,161 mg of short-chain omega-6. That amount of corn oil is even higher in short-chain omega-6 with 7,888 mg. By comparison, canola oil has considerably less, 2,842 mg -- but some experts, including Dr. Mary Enig, are concerned enough about canola oil to call it "The Great Con-ola" and "a poisonous substance, an industrial oil that does not belong in the body." Dr. Enig is vice president of the Weston A. Price Foundation and the author of Know Your Fats: The Complete Primer for Understanding the Nutrition of Fats, Oils, and Cholesterol, (Bethesda Press, 2000). The fourth big one, cottonseed oil, is almost as high as corn oil with 7,004 mg.
We have others that we can use for cooking. For example, olive oil has many redeeming values. And it has only 356 mg of short-chain omega-6 per tablespoon. Coconut oil is even better with just 81 mg. Macadamia oil is likely to have even less, but we have no official measurements by the U.S. government, and this oil is expensive.
The gold standard for finding nutrition data for thousands of foods is the U.S. Department of Agriculture's National Nutrient Database. It's online at http://www.nal.usda.gov/fnic/foodcomp/search/
But when we use the USDA's tables, we can check only one food at a time. The USDA also uses the technical terms for the many types of omega-3 and omega-6 fats. When I use those tables, I still have to use a cheat sheet: