“EFAs” and “Omega -3 fatty acids” are very often recommended for a variety of inflammatory disorders. Not all fatty acids are created equal.
Fatty acids are required for normal cellular function. The essential fatty acids (or EFAs - those that must be provided in the diet to prevent nutritional deficiency) are linoleic acid and alpha linolenic acid for dogs. Cats require linoleic acid, alpha-linolenic acid and arachadonic acid.
Essential fatty acids come from plant and animal fats. The types most usable for animals are described as omega-6 fatty acids and omega-3 fatty acids. The omega-3 fatty acids, when incorporated into the cells of the body, tend to influence cells to make less inflammatory responses. When omega-6 fatty acids accumulate in cells, the responses they make to threats are more inflammatory. When an animal has a chronic, abnormal inflammatory condition such as allergies or autoimmune diseases, the better scenario is to have the cells full of omega-3 fatty acids for less inflammation and better comfort.
The most anti-inflammatory omega-3 fatty acid is EPA (eicosapentanoic acid), contained in fish, krill and algae oils. DHA (docosahexanoic acid) is also contained in fish oil, and we tend think of it therapeutically for its effects in the nervous system - studies have shown that it helps puppies learn better and may improve cognitive dysfunction as well. Flax seed oil contains ALA (alpha linolenic acid), which is not nearly as potent as EPA. A single exception to the omega-6 fatty acid rule is GLA (gamma linolenic acid), which is an ANTI-inflammatory omega-6 fatty acid.
We use fish oil for high EPA content. Flaxseed oil contains 55% ALA but unfortunately, it is converted inefficiently to EPA by its enzyme, delta 6-desaturase, and is not a strong anti-inflammatory fatty acid. And cats don't have much delta 6-desaturase compared to dogs and people.
GLA is contained in evening primrose oil at 8-10% concentration, in black currant seed oil at 17%, and in borage oil at 23%.
So - can we use flax seed oil for inflammatory disorders like arthritis, cancer, or allergies? Yes - in dogs - but it won't work as well as fish oil with its preformed EPA. Can we use the high GLA oils for inflammatory disorders? Yes, but the study results seem inconsistent so far as to whether they work. My preference is fish oil.