-3 fatty acids are named by nutritionists by virtue of the fact that the last double bond is found 3 carbons from the methyl end of the fatty acid. A prominent example is linolenic acid. -3 fatty acids are found in relatively high amounts in fish oils compared to red meats and are intensely studied, because they tend to depress levels of both serum cholesterol and triacylglycerols. (Conversely, diets high in saturated fatty acids, such as stearic acid, tend to elevate serum cholesterol levels.)

Current evidence suggests that linolenic and other -3 fatty acids act by somehow competing with the metabolism of arachidonic acid, which is the principal precursor of the prostaglandins and thromboxanes.