Persistence of rat nocturnal feeding and drinking during diurnal presentation of palatable diet.

Male laboratory rats were fed a highly palatable diet during the light phase of a 12:12 LD cycle. Nocturnality of feeding was reduced from approximately 77% of the total daily intake to 56%. Increase in diurnal feeding was attributable to the ingestion of a large meal at the beginning of the L phase. Reduction of nocturnal feeding was attributable to decreased ingestion in the first 3 hr of the D phase. Outside these times the daily feeding pattern was unmodified. These findings do not represent a reversal of the feeding rhythm as previously reported, but a modification which is not consistent with interpretation as a phase-shift. Throughout the testing period total daily food intake remained unchanged and body weight was defended despite the increase in calories ingested. Daily drinking patterns and total daily water intake were not significantly altered by the experimental manipulation.