Typical diets in developed countries deliver large amounts of saturated fatty acids and the polyunsaturated omega-6 linoleic and arachidonic acids and low levels of omega-3 fatty acids. Throughout evolution, humans were accustomed to diets providing roughly equal amounts of omega-6 and omega-3 fatty acids. However, during the last 200 years, the ratio of dietary omega-6:omega-3 fatty acids increased from about 1:1 to 20-25:1. Leading health professionals now recommend ratios between 4:1 and 10:1. A healthy balance of dietary omega-6 and omega-3 fatty acids appears to be a prerequisite for normal immune function. Dietary linoleic acid (18:2 omega-6) is a precursor to arachidonic acid (20:4) which in turn is a precursor for pro- inflammatory prostaglandin E2 and leukotriene B4, and platelet aggregating thromboxane A2. The omega-3 fatty acid ALA provides a natural counterbalance, because it is metabolized to the long chain omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), which serve as precursors for the anti- inflammatory prostaglandins E1 and E3, and decrease the formation of prostaglandin E2 and thromboxane A2. Among other factors, sufficient dietary levels of ALA and other omega-3 fatty acids are also important for healthy mucous membranes, skin and hair, and serve as precursors for steroid production and hormone synthesis.