"The Moss Reports newsletter errs when it says, in the second of these sentences, For vegetarians, getting sufficient amounts of DHA and EPA can be a challenge. The best sources are walnuts, flaxseeds and flaxseed oil, olive oil, canola (rapeseed) oil, and avocado.
"According to USDA's authoritative Nutrient Database for Standard Reference, none of these foods have any DHA or EPA (0.00 grams per 100 grams). What they do have (what you evidently were thinking of), is alpha-linolenic acid (LNA), a short-chain omega-3 fatty acid that our bodies convert very poorly into longer-chain EPA and then potentially to DHA. The conversion percentage is debated, but low, perhaps 10%. It is not large enough, for example, for infants to fully meet their needs for DHA from LNA. This is why DHA is added to infant formulas.
"LNA varies widely in the sources you mention, from 0.13 grams per 100 grams in avocados, to 53 grams per 100 grams in flax oil, according to USDA.
http://www.nal.usda.gov/fnic/foodcomp/search/
Another reader, Mr. A.B., comments: "The seeds of Chia (Salvia hispanica L.) are a good and cheap source of omega 3 fat and other valuables. Chia seeds contain oil amounts varying between 32-39%, with the oil offering the highest known natural percentage of alpha-linolenic fatty acid (60-63%). Alpha-linolenic acid is an essential fatty acid acting in the human body as a substratum for the transformation into EPA and DHA through the action of desaturation and elongation enzymes. The seeds also contain some omega-6 essential fatty acids and exhibit a favorable omega-3 to omega-6 ratio of 3:1. Modern diets contain too few omega-3 fatty acids. The seeds possess 19-23% protein and the amino acids of chia protein have no limiting factors in the adult diet (i.e., they are a complete protein source providing all of the essential amino acids in an appropriate balance)."
