To determine the effect of under-nutrition during suckling in adults, at delivery female Sprague Dawley rats were allowed to lactate litters of either eight (controls) or sixteen pups each (large litter, LL). The amount of milk taken by LL pups was less than the controls and the concentration of triacylglycerols (TG) in the milk of the former was lower. The increase of both body weight and length in LL was lower than in the controls during suckling. At weaning, pups were allowed to eat ad libitum a standard diet and whereas at 20 months female body weight did not differ between LL and control rats, LL males weighed less than controls. Plasma NEFA were lower in male LL than in controls at 10 months, leptin at 10 and 16 months and TG and VLDL-TG at 20 months, with no differences in females. When 20 months old, lumbar and epididymal adipose tissue weights were lower in male LL than in controls, but not in females. The increase in plasma insulin after oral glucose load was lower in LL than in controls, both in males and females at 4 and 16 months, and only in males at 10 months, whereas the change in plasma glucose remained constant between the groups. Results indicate that both the pancreatic β-cell function and insulin sensitivity and adipose tissue metabolism are independently programmed as a consequence of under-nutrition during suckling, the effect being more manifest for males than for females.