Effect of dietary fat on whole body fatty acid synthesis in weanling rats.

The effect of dietary fat on body composition, whole body lipogenesis, and enzyme activity was measured in rats over the first 16 weeks post-weaning. Rats were fed either a low fat (5% w/w fat) or high fat (20% w/w fat) diet for the first 4 weeks. After this time all rats were fed the low fat diet. The results showed no significant effect of diet on the rate of fat synthesis over the first 8 weeks of the experiment. However, the activities of the enzymes of fatty acid synthesis [glucose 6-phosphate dehydrogenase, malic enzyme, adenosine triphosphate-citrate lyase, acetyl-coenzyme A carboxylase (ACCX), fatty acid synthetase] were dependent on the age and dietary status of the animals. The exact pattern depended on the specific enzyme and the tissue source. No significant differences in pyruvate dehydrogenase (PDH) activity were observed. Mathematical analysis of the enzyme activities suggested that ACCX and PDH were the most likely sites of fat synthesis regulation. In addition, an examination of body composition and overall weight retention showed that the "weight increasing" effect of a high fat diet could be completely reversed by subsequent feeding of a low fat diet. However, the reversal required an additional 12 weeks. Interestingly, at this time the rats switched from a high fat to a low fat diet had a lower body weight and lower body fat content than rats fed a low fat diet throughout the course of the experiment.