Sex differences in energy metabolism in pre-pubescent, early pubescent and adult rats

This study was intended to investigate sex differences in response to a high fat (HF) diet at three stages, pre-puberty, early puberty, and adulthood.

Body weight, energy intake, glucose, insulin, and leptin concentrations were measured in male and female rats that were fed either a HF or a control chow during each stage of development. The sex hormones of adult rats were also examined. In addition, metabolic factors of male rats pair-fed with females were evaluated.

At pre-puberty, the average body weight of pups born to a HF dam exceeded that of the control, whereas there were no significant differences in body weight between males and females. During early puberty and among 15-wk-old rats, males exhibited greater weight gain with higher energy intake than did females. During all three stages, HF rats exhibited significant increases in body weight, insulin and leptin concentrations. Estradiol levels of females were higher than those of males, and those of the HF groups were significantly lower than the control groups. Although the body weight gain in male rats pair-fed with females exceeded that of the females, the insulin and leptin levels of pair-fed HF males decreased to the control levels.

HF male rats became obese earlier than HF females. This result may be the result of differences in estradiol levels between males and females. The decline of insulin and leptin levels in pair-fed male groups indicates that caloric restriction among male rats could reduce the incidence of metabolic diseases.