Yeah, your body has adjusted, so you need to change the other side of the equation; namely burn off more calories. You must always escalate the training in order to keep body's development continuous. YOu need to add more intense training. Do strength-building in the gym, sprints and intervals on the bike. Hi-intensity training raises your basal metabolism for hours after the workout and continues to burn off calories. Then also do real endurance rides of 3-4 hours once or twice a week. The 3rd to 4th hours burn off way more fat calories than the 1st two.