Do saturated or unsaturated fatty acids have double bonds?

Unsaturated fatty acids are characterized by the presence of one or more double bonds between carbon atoms in their hydrocarbon chains. These double bonds introduce kinks in the fatty acid chains, preventing the molecules from packing closely together, which often results in these fats being liquid at room temperature.

In contrast, saturated fatty acids do not have any double bonds; all carbon atoms in their chains are fully saturated with hydrogen atoms. This leads to a straight and linear structure, allowing saturated fats to pack more tightly together, typically resulting in a solid state at room temperature. Therefore, when considering the definition and structure of fatty acids, unsaturated fatty acids are the correct answer because only they contain the double bonds that define their unsaturation.