The Metabolic Effects of Aging, Phenotype and Carbohydrate Feeding on Caloric Efficiency and Adiposity in the LA/Ntul//-Cp Rat

The purpose of this study was to assess the effect of aging and obese phenotype on CE and adiposity and to determine if the impaired responses to diet in the obese phenotype were associated with corresponding changes in CE which might be correlated with the greater adiposity associated with the (-cp) trait. Obesity develops in the obese phenotype of the LA/Ntul//-cp (corpulent) specific pathogen- free rat strain by 5 to 6 weeks of age. Groups [n=12 -20 rats/phenotype] of female congenic lean and obese LA/Ntul//-cp (corpulent) rats were fed ad libitum standardized Purina diets for 4, 14, or 24 months or the same diet plus a 16% (w/v) sucrose solution supplement from 12 weeks of age, and measures of body weight, caloric intake, and caloric efficiency (CE) determined at each age group. Body weights of lean animals remained similar at all ages studied, while body weights of obese phenotype were significantly greater than their lean littermates at each age studied. The sucrose supplement was without significant effect on final body weights in the lean phenotypes at all ages studied (p=n.s.) but were associated with greater body weights at ages 4, 14 and 24 months of age in the obese phenotype (p=<0.05). CE was determined as the ratio of kcal/gram of body weight per day remained relatively constant in lean animals throughout the age range, but CE was more efficient in the obese phenotype at all ages studied and became progressively more efficient with the sucrose supplement feeding with increasing age. The findings of this study show that CE is linked to a higher efficiency of energy utilisation and/or energy conservation in the obese phenotype of this strain than in the lean phenotype, and that the metabolic impact of added sucrose was linked to an additive effect on the CE of weight gain and adiposity in the obese. It is concluded that the autosomal recessive nature of the -cp trait was associated with a greater economy of caloric efficiency and marked adiposity which was further enhanced by aging and compounded by the addition of a sucrose supplement, but was independent of derangements in appetite dysregulation per se.