Female rats require greater energy deficit for body weight reduction than males

Abstract

Whether decreases in lean tissue (LT) and adipose tissue (AT) during body weight (BW) reduction differ between males and females is unclear. To investigate sex differences in changes in body composition and energy deficits during BW reduction, sexually mature 15-week-old rats were divided into a group euthanized before BW reduction (n = 6 males, n = 7 females) and a group euthanized after three days of fasting (n = 6 males, n = 6 females). Energy expenditure and BW were measured during the study period. Losses in lean tissue (ΔLT) and adipose tissue (ΔAT) were calculated using simultaneous equations based on ΔBW, which is the sum of ΔLT and ΔAT, and the energy lost from the body is the sum of the energy lost from ΔLT and ΔAT. BW reduction was significantly greater in males than females, total energy expenditure was significantly greater in males than females, and the energy required to reduce BW by 1 kg was significantly less in males (3304.8 kcal/kg [SD 327.5]) than females (3893.0 kcal/kg [SD 356.5]). Both ΔLT and ΔAT were significantly greater in males than in females. The ΔLT:ΔAT ratio was significantly different between males (67:33) and females (57:43). Sex differences exist in the metabolic responses to BW reduction, and females lose more energy-dense adipose tissue during BW reduction than males, demonstrating that a greater energy deficit is required to reduce BW in female rats than male rats.

Keywords

• body weight reduction
• energy expenditure
• lean tissue
• adipose tissue