Whole body fatty acid synthesis and fatty acid intake in young rats of the Zucker strain (Fa/- and fa/fa).

The rate of whole body fatty acid synthesis was measured in immature (18- and 25-day-old) lean and obese male Zucker rats. The effect of stress and diurnal variation on the rate of fatty acid synthesis was also determined in 25-day-old animals. In addition, the intake of fatty acid from the diet was also determined. At 16 and 18 days the carcase of the obese rat contained significantly more lipid than its lean counterpart. In neither phenotype was there any significant lipid deposition from 18 to 23 days. Over the period 23 to 27 days the obese rat deposited approximately six times more lipid than its lean counterpart. Consistent with this finding is the observation that at 25 days the obese rat synthesized at least four to five times more fatty acid than its lean littermate. There was no phenotypic difference in the rate of fatty acid synthesis at 18 days. It is suggested that the young obese rat becomes obese before weaning because of a reduced oxidation, and hence increased storage, of dietary fatty acid. After weaning, although this unusual partition persists, hyperlipogenesis is the main cause of the further development of obesity.