Effect of high fat weanling diets containing either medium-chain triglycerides or long-chain triglycerides on the development of obesity in the Zucker rat.

Zucker rats were early weaned onto either medium-chain (MCT) or long-chain triglycerides (LCT) to examine the effect on the development of obesity. Preobese and lean pups were weaned at 16 days to isocaloric, isonitrogenous liquid diets containing either 65% MCT or LCT (by calories) or to a "stocklike" (5.5% fat, 72.6% carbohydrate) control diet or were pair-fed stocklike diet to MCT-fed rats until day 45. MCT-feeding lowered body weight gain and fat pad weight in obese and lean rats compared to stocklike-fed controls. Additionally, fat cell size and lipoprotein lipase (LPL) activity and hepatic acetyl CoA carboxylase activity were reduced in obese MCT-fed rats compared to obese controls fed stocklike diet. Except for altered LPL activity the effects produced by MCT-feeding were attributable to its anorectic effect. However, all obese rats, including the MCT group, developed an obese body composition and were hyperinsulinemic. The development sequence leading to obesity may be derived from a fundamental cellular defect that results in metabolic alterations in different tissues at critical periods of development. Thus, effective treatment of this genetic obesity requires a better understanding of fa gene action.