Body fat accretion: a rat model

A rat model for studying causes of body fat accretion was developed. Employing this model, it was possible to produce a 108 g difference in carcass fat content between two groups of rats simply by selecting the seven fattest and the seven leanest animals from a group of 100. The results of this study provide evidence that the gastrointestinal tract was not a site of caloric wastage, that total energy excreted in feces and urine was directly proportional to caloric intake, that differences in brown adipose tissue thermogenesis were not responsible for the twofold difference in adiposity between the lean and fat rats, and that a family of hepatic lipogenic enzymes was not up-regulated even though the habitual consumption of a diet rich in carbohydrate was greater in the fat vs lean rats. The fat rats also had a greater lean body mass. Therefore, the additional calories consumed by the fat rats could have contributed to their greater adiposity and/or could have been channeled to sustain more active tissue. Finally, evidence was presented to show that the experimental selection process is an important consideration when determining the relationship between caloric intake and body fat content.