Prediction of basal metabolism from organ size in the rat: relationship to strain, feeding, age, and obesity.

Use of the weight of various organs and tissues together with their specific metabolic activity for prediction of basal metabolism (BM) seems to be promising. In this study we compared the use of this method with those based on simple or multiple regression analyses. We observed that 97.4% of differences in BM in a group of nine adult male Wistar rats weighing 273--517 g could be accounted for by changes in tissue and organ weights. BM measured in lean Zucker and Sprague-Dawley rats did not diverge from the prediction of the model by >1.6%. According to the organ-based model as well as multiple regression analyses, but not simple regression analyses, BM was increased 18--21% in young rats, decreased 6--7% in food restricted/refed rats, and decreased 19--21% in aged rats. Only with obese rats did the predictions of the two methods diverge. The main reason for this discrepancy seems to be the way adipose tissue size and metabolism are taken into account.