I have been doing IF since the original horizon programme and have been maintaining my BMI at 24. Occasionally it goes up too much. Recently on a total fast day (0 calories) I also did high intensity training in the evening (ie 24hours after starting fast) of 3x 20 second maximal bursts on a spin bike and lost 10lbs weight in 24 hours from morning to morning. It clearly has a synergistic effect.