Fats have energy-storing, structural and regulatory roles in the body (Table 25.1). Depots of white adipose tissue (WAT) therefore not only function to store energy but also to provide precursors for synthesis of other species. Specific roles are played by certain fatty acids in this regard. For example, long-chain derivatives of the essential fatty acids of the omega 3 series (which cannot be synthesised de novo but must be taken in through the diet and modified) contribute to membrane formation in the CNS and the retina. The importance of the roles played by omega 3 fatty acids in anchoring specific membrane proteins involved in signalling is illustrated by the effects of dietary deficiencies. About ⅔ of the total content of docosahexaenoic acid (22 carbon fatty acid derived from linolenic acid) are assimilated in the final three months of gestation and the remaining ⅓ during the first three months of life. An interruption of supply during these crucial periods produces a measurable adverse effect on the development of cognitive function and of visual acuity.