Daily rhythms of feeding in the genetically obese and lean Zucker rats.

Feeding patterns were examined in obese (fa/fa) and lean (Fa/-) adult Zucker rats over the light-dark cycle during 14 days. Obese rats eat more than lean rats especially during the dark phase. Light and dark feeding expressed as percentage of 24 hr intake showed no significant differences between the lean and obese groups. The higher food intake in obese rats is mainly caused by larger meals since obese rats ate fewer meals than lean rats. Only for the obese group differences were observed between mean meal size in light and dark phase. There is some indication that the circadian controlled temporal distribution of meals is different in obese rats compared to lean rats since obese rats eat fewer but larger meals during the first half of the dark phase. During this phase meal size increases gradually in the obese rats, suggesting that the circadian influence on feeding motivation is increased.