Alterations of energy and substrate metabolism in rats with large and sustained changes in daily food intake.

Energy expenditure was measured in one-way crossed-intestine rats by use of indirect calorimetry to examine the role of energy metabolism in body weight control. The intestinal surgery was done according to Koopmans (Brain Res. Bull. 14: 595-603, 1985). The food-losing rats increased daily food intake from 70.8 to 126.3 g/day, whereas their partners decreased intake from 67.1 to 38.7 g/day (P < 0.001). Compared with levels before surgery, the food-losing rats showed slightly increased O2 consumption (1.31 vs. 1.28 1.h-1.kg-1) and metabolic rate (6.62 vs. 6.39 kcal.h-1.kg-1) and largely increased CO2 production (1.31 vs. 1.22 l.h-1.kg-1, P < 0.01), whereas in their food-gaining partners O2 consumption (1.12 vs. 1.25 l.h-1.kg-1, P < 0.01) and metabolic rate (5.76 vs. 6.26 kcal.h-1.kg-1) were significantly decreased. Respiratory quotients were higher in the food-gaining rats than in their partners (1.076 vs. 0.999, P < 0.01), indicating more fatty acid synthesis. These results suggest that daily food intake and energy expenditure increase and decrease together, despite the fact that about the same amount of food has been absorbed from the intestines of each rat.