[Uptake of utilizable food energy by light-weight and heavy-weight rats fed a low-fat or high-fat diet].

The uptake of utilizable dietary energy (DE) as affected by diet (containing 3 or 50% (w/w)fat), body mass (BM) and age was investigated in male Wistar rats. In comparing heavy-weight animals fed the high-fat diet (HFD) with light-weight animals fed the low-fat diet (LFD) (differences in BM up to 60%), it was found that the uptakes of DE calculated on animal were significantly higher (up to 55%) in the HFD animals than in the LFD animals; but there were no significant differences when the uptakes of DE were calculated on 100 g BM. Thus, the LFD rats (the diet of which contained a high proportion of protein (70% (w/w)) exhibited no reduced uptakes of utilizable DE as compared to HFD rats. Of the heavy-weight LFD animals and the light-weight HFD animals which showed virtually no differences in BM, the HFD animals take up more utilizable DE (per animal or per 100 g BM) than the LFD animals. This difference, which amounts to 60%, is statistically significant. The comparison of the uptakes of DE/animal/100 g BM by light-weight rats with those by heavy-weight rats fed the same diet showed that the uptakes by the heavy-weight animals were in most cases significantly greater. Consequently, the greater BM of the heavy-weight animals of the respective diet groups must be attributed to more efficient utilization of feed. This is also indicated by the fact that the light-weight HFD animals excret more fat in the faeces than the heavy-weight animals. The amount of fat excreted by the HFD animals is some 10-fold greater than that excreted by the LFD animals. However, when the amount of excreted fat is expressed in % of ingested dietary fat, the fat excretion is of the same order of magnitude on both diets.