Fatty acids are aliphatic monocarboxylic acids derived from , or contained in , an animal or vegetable fat , oil , or wax . Natural fatty acids commonly have a chain of four to 28 carbon atoma ( usually unbranched and even numbered ) , which may be saturated or unsaturated . Hydrogenation of unsaturated fatty acids is widely practiced to give saturated fatty acids , which are less prone toward rancidification .