Fatty acid oxidation and fatty acid synthesis in energy restricted rats

The importance of fat oxidation and fatty acid synthesis were examined in r ats fed approximately one half their nd libitum food intake for a period of 13 days followed by 7 days of ad libitum feeding (refed rats). This study was undertaken because previous reports demonstrated that refed rats rapidl y accumulated body fat. Our results confirmed this observation: refed rats accrued body fat and body weight at rates that were approximately 3 times h igher than controls. Evidence for a period of increased metabolic efficienc y was demonstrated by measuring the net energy requirement for maintenance over the refeeding period: refed rats had a reduced metabolic rate during t he period of energy restriction (approximately 30% lower than control) and this persisted up to 2 days after the reintroduction of nd labitum feeding. The major factor responsible for the rapid fat gain was a depressed rate o f fatty acid oxidation. Calculations of protein and carbohydrate intake ove r the refeeding period showed that the simplest explanation for the decreas e in fatty acid oxidation is fat sparing. This is possible because of the l arge increase in dietary carbohydrate and protein intake during the refeedi ng period when metabolic rates are still depressed. The increased carbohydr ate and protein may adequately compensate for the increasing energy require ments of the ER rats over the refeeding period affording rats the luxury of storing the excess dietary fat energy. (C) 2001 Elsevier Science Inc.. All rights reserved.