The key link between fatty acids and atopic diseases is hat a number of the mediators which play a role in these diseases are synthesized from arachidonic acid (20:4n-6). This fatty acid is consumed in relatively low quantities in the human diet (<300 mg per day) yet in many inflammatory and immune cells it constitutes more than 20% of the fatty acids present in the membrane phospholipids.

Thus, much of the arachidonic acid found in cells is synthesized (most probably in the liver) from linoleic acid (18:2n-6), a major component of vegetable oils and products made from them; a typical Western diet provides approximately 10-15g of linoleic acid per day.

Once consumed, linoleic acid is metabolized by the enzyme Delta6-desaturase to gama-linolenic acid (GLA; 18:3n-6), then to dihomo-gamma-linolenic acid (DGLA; 20:3n-6) and then to arachidonic acid (Fig. 1).