Fatty acids in the body arise either from biosynthesis from acetyl-CoA or from breakdown of fats and phospholipids. Free fatty acids are rarely found in the body. Fatty acids are transported in the blood complexed to serum albumin. Fatty acids can be saturated (no double bonds) or unsaturated (contain double bonds). Unsaturated fatty acids of biological origin predominantly contain cis double bonds. Mammals are unable to synthesize some fatty acids, making these fatty acids essential components of their diet.
Common saturated fatty acids include palmitic acid and stearic acid. Common unsaturated fatty acids include oleic acid, palmitoleic acid, linoleic acid, linolenic acid. The fatty acid, arachidonic acid, is a precursor of the prostaglandins.