It is a common dogma that gastric bypass (GB) induces early satiety and consequent reductions in food intake and nutrient absorption. The aim of the present study was to analyze feeding behavioral and metabolic changes in rats after GB.

Male Sprague–Dawley rats at the ages of 23 and 42 weeks were placed in metabolic cages connected with a comprehensive laboratory animal monitoring system. At the age of 48 weeks they were subjected to either GB or sham operation, and then placed in metabolic cages at 51 and 62 weeks (or 3 and 14 weeks postoperatively).

GB rats lost 20% of the body weight within 2–3 weeks and remained at this lower level until the end of the study at 14 weeks postoperatively. Satiety ratio was higher during daytime than nighttime in both sham-operated and GB rats, but was not significantly different between the two groups. Neither daily accumulated food intake nor food intake per 100 g of body weight was different between sham-operated and GB rats. Apparently, GB rats ate more frequently during daytime and had smaller meal size during nighttime at 3 weeks postoperatively. These changes were not present at 14 weeks postoperatively. Energy density in the feces was the same in GB and sham-operated rats postoperatively. Energy expenditure declined with age, but increased in GB rats compared with age-matched sham-operated rats.

GB reduced the body weight without causing early satiety, reducing food intake or inducing malabsorption. It did, however, increase energy expenditure.