Resistance to dietary obesity in rats given different high-energy diets

Susceptibility to dietary obesity was studied in Wistar and Sprague-Dawley rats submitted to different high-energy diets. Experiment 1: female Sprague-Dawley rats were fed chow (n = 6) or a high-fat diet (n = 12) for 22 weeks. Experiment 2: Wistar rats were fed chow or a high-fat diet, and Sprague-Dawley rats were given chow, high-fat, sweet condensed milk, or cafeteria diets, for eight weeks (6 animals per group). Food intake and body weight were recorded weekly. Adipose tissue was collected from periovarian, mesenteric, and subcutaneous regions and adipocytes were isolated and measured. Both strains showed similar energy intake and body weight gain. Wistar rats reached greater final body fat contents than Sprague-Dawley rats, regardless of the type of diet. However, resistance to dietary obesity was found in 100% of cases in both experiments. None of the diets succeeded in increasing body fat accumulation when compared to control groups. All adipose tissue locations were equally unaffected, with periovarian fat cells being larger than those in mesenteric and subcutaneous regions in all the groups. In view of the strong resistance to obesity observed in rats, it should be important for researchers to transmit the difficulties of inducing dietary obesity in these animals, in order to prevent bias in science interpretation.