about 100 g of glucose/d are irreversibly oxidized by the brain from the age of 3–4 y onward. However, this excludes recycled carbon, gluconeogenic carbon, for example from glycerol, and it does not account for glucose used by other non-CNS tissues. For example, in the adult, muscle and other non-CNS account for an additional 20–30 g of glucose daily. For this reason a safety margin of 50 g/d is arbitrarily added to the value of 100 g/d