The major problem of flaxseed oil is that it has the fatty acid ALA (alpha-linolenic acid). As we take the flaxseed oil the ALA is transformed into Omega 3 by our bodies. Opposed to flaxseed oil, the fish oil contains pure Omega 3. Why is it a problem? Well, some people with poor health may have difficulties in transforming the ALA to Omega-3. Therefore, they may not really benefit from flaxseed oil. In such cases, fish oil is the best choice.