Fasting plasma triglyceride levels and fat oxidation predict dietary obesity in rats

We investigated whether fuel metabolism prior to high-fat feeding differs in outbred Sprague-Dawley rats either prone or resistant to diet-induced obesity. Chow-fed rats were deprived of food, and blood was collected 12, 18, and 24 h later. Rats were then fed a high-fat diet ad libitum for up to 4 weeks to assess weight gain. Blood samples were analyzed for a variety of metabolic fuels and hormones. Only fasting plasma triglyceride concentrations showed a positive correlation with the weight gain during the high-fat feeding period, with concentrations after 18 h of fasting showing the most consistent relationship to weight gain. Body weights and fat pad weights did not correlate with fasting plasma triglyceride concentrations before high-fat feeding. The amount of 14CO(2) recovered from gavaged [14C]palmitic acid in chow-fed rats negatively correlated with weight gain during the subsequent period of high-fat feeding. These results show that there are preexisting differences in fat catabolism that may underlie differential susceptibility to diet-induced obesity; in particular, fasting levels of plasma triglycerides and fatty acid oxidation may be early predictive markers for this susceptibility.