Refeeding after prolonged fasting in rats: nycthemeral variations in dietary self-selection.

The influence of metabolic status on food selection during refeeding after fasting was investigated in rats fasted for a long period of time and subsequently given the choice of eating fat, protein, and carbohydrate individually. Rats were fasted until either metabolic phase 2 (essentially using lipids) or metabolic phase 3 (when there was a rise in protein utilization). The very large first meal of the refeeding was identical in the two groups of animals and consisted mainly of fat and protein. The observed diurnal hyperphagia persisted for 2 days in phase 2, while in phase 3 the hyperphagia persisted throughout the 8 observation days. Both periods of hyperphagia consisted of an increase in fat and in protein intakes. The nocturnal intake was increased, but to a lesser extent, on days 4 and 5 in phase 2 and on days 4, 5, and 6 in phase 3. These results can be related to the metabolic events present during the diurnal part of the nycthemeral cycle.