Fatty acids and particularly, polyunsaturated fatty acids are essential constituents of biological membranes. Apart from this, they fulfil functions as signalling molecules, anti- freezing compounds and energy storage. While a lot of research has been conducted on the changes in lipid content that occur during fasting, only few studies have focused on changes in the quality of body lipids. During fasting and any extended period of diminished energy intake such as starvation, the fatty acid composition of the lipids is altered: fat mobilisation, transport and oxidation all work together and induce an apparent “fasting fatty acid response” with saturated fatty acids being largely retained whereas monounsaturated and polyunsaturated fatty acids are largely mobilised and thus decreased in stored triacylglycerols. In the presentation, this pattern will be explained in more detail in a variety of animals in the light of the existing literature on the subject. We will examine changes in whole- animal, adipose and muscle fatty acid composition that occur during fasting/starvation. We will also discuss the selective retention of C 18:2 n-6 in white adipose tissue of hibernating animals that seems to be related to physiological heterothermy and not starvation per se. We conclude that the observed changes in fatty acid composition are unlikely to represent an adaptive “starvation response”. While triacylglycerols seem to change in an unregulated manner in response to fasting and starvation, membrane fatty acid composition is changed more systematically when an animal is restricted calories. Future research might shed light on this subject and should emphasise the separation of lipid fractions (triacylgylcerols vs. phospholipids) in the various tissues.