Ontogenetic trajectories from weaning to adulthood and sex differences in feeding patterns were examined in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an animal model of early onset overeating-induced obesity, and a natural cholecystokinin-1 receptor knockout. Overnight patterns of licking a palatable liquid diet (Ensure) were analyzed on Postnatal Days 22, 38, 60, and 90. Because different microstructure profiles may reflect alterations in the influence of positive and negative signals, we examined meal parameters to uncover developing mechanisms underlying eating behavior in this strain. OLETF rats displayed significantly greater caloric intake, larger meals (in number of licks), and more (within-meal) clusters of feeding (which were shorter in duration and contained fewer licks per cluster) than did Long-Evans Tokushima Ohtsuka (LETO) strain controls. OLETF rats also had significantly lower satiety ratios than LETO rats. Moreover, we identified sex differences in the age of emergence of microstructural patterns of obesity-related overeating, suggesting that systems other than cholecystokinin may be disrupted, possibly worsening the OLETF strain's obesity phenotype.