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Sunday, February 11, 2007

Omega-3 Fatty Acids

Omega-3 fatty acids include:
  • 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.

Originally it was thought that the ALA would be beneficial as it is converted to the beneficial EPA and DHA in the body; however, now it is thought that the conversion is inefficient so rather than being left with EPA and DHA one is left with substantial ALA. Unfortunately, one study [PMID: 8158682] concluded that those with the highest levels of ALA in their blood had 3x the risk of prostate cancer as those with undetectable levels and another study [PMID: 15213050] concluded that those with the highest consumption of ALA had 2x the risk of prostate cancer.

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].

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