Fatty acids are important sources of body fuel. When metabolized, they yield large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids.
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 atoms (usually unbranched and even numbered), which may be saturated or unsaturated. This would include acetic acid, although this is not usually considered a fatty acid (not a lipid).
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Fatty acid Facts for Kids. Kiddle Encyclopedia.