Does prolonged exercise alter diet-induced thermogenesis?

Diet-induced thermogenesis (DIT) is mainly an insulin-mediated response and the result of fat and glycogen synthesis. We investigated DIT at rest and after exercise to clarify the mechanism of exercise-induced changes in DIT in 6 healthy men (mean age 36 +/- 16 years). Subjects exercised for Ih at 5 8% of maximal O-2 consumption on a bicycle ergometer and then rested for 8 h sitting in a comfortable chair (exercise experiment). On a different day, subjects rested for 8 h without preceding exercising (non-exercise experim ent), At 12.30 h, the subjects were given their second meal. DIT to individ ual meal did not differ significantly between the exercise and non-exercise days. Increased insulin sensitivity and increased free fatty acid oxidatio n by exercise may facilitate the conversion of glucose to glycogen in muscl e. On the other hand, insulin secretion expressed as the ratio of plasma le vels of insulin to glucose after the meal was significantly decreased in th e exercise experiment (p < 0.05), Study of heart rate variability showed th at sympathetic tone, a primary hormonal determinant of glucose metabolism d uring exercise, was increased and parasympathetic tone was decreased during the recovery period in the exercise experiment (p < 0.05). These findings suggest that changes in DIT are affected by many factors and may be related to the balance between these counteracting factors.