- Alpha-linolenic fatty acid (ALA; 18:3n-3) is found in meat, dairy, flaxseeds, canola oil, safflower oil, cottonseed oil and other polyunsaturated oils and certain other vegetable and seed oils.
- Eicosapentaenoic fatty acid (EPA; 20:5n-3) and docosahexaenoic fatty acid (DHA; 22:6n-3) are found in fatty fish such as salmon, sardines and herring and are thought to be highly beneficial to health.
A discussion of the above and references to the original literature are provided on page 5 of this UCSF report: UCSF Report and on page 30 of this Prostate Cancer Foundation Report
Complicating the picture are the following items pointed out in the UCSF report:
- ALA is an essential fat so one would not want to cut it out entirely
- the primary sources of ALA in these studies were red meat, milk, butter,
mayonnaise and margarine (and not flax or flaxseed oil)
Thus obtaining EPA and DHA from fish would appear to be advantageous (modulo pollution) but the degree to which flax and flaxseed oil are harmful or beneficial is not clear.
The following sources contain tables of ALA, EPA and DHA fat content for various foods and fats: [Table] and [Table].
Note that there is some discussion here that flax is problematic for those on 5AR2 inhibitors: [discussion].