Conditions of low insulin (fasting, infancy, ketogenic diet) result in mobilization of fatty acids from adipose tissue. Some of the released fatty acids are easily β-oxidized for energy (α-linolenate, linoleate, palmitate, oleate; see Fig. 5) and for ketogenesis (especially ALA). The carbon from these fatty acids reaches the brain indirectly through ketones (INDIRECT route). Other fatty acids released from adipose tissue are much less beta-oxidized and are not ketogenic, i.e. docosahexaenoic acid (Raclot and Groscolas, 1993; Taha et al., 2005) and arachidonic acid. These fatty acids reach the brain directly (DIRECT route). These two processes (fatty acids for ketogenesis for brain energy and fatty acids for brain membrane integrity) contribute to the brain’s Yin and Yang; both are needed for optimal brain development in infants and potentially for optimal treatment of certain neurological diseases including epilepsy (Voskuyl, 2002) and Alzheimer’s.