If you are cycling just for exercise (not to get to work) for about 40 minutes (as opposed to over 1 hour) and desire to "lean out" without planning to lift weights before or after, I would suggest not eating until you are done. The reason is if you eat before you workout, as you digest (another possible issue...), you will increase your glucose which will fuel your workout. This is ok, but (at least theoretically) if you exercise right out of bed you will theoretically quickly use up your glucose stores (the sugars in your blood) within 20 minutes, then you will start burning fat.
The above applies only to shorter workouts. For long rides, like 60 miles, I fuel up with a double dose of oatmeal and eggs 2 hours before riding. This way, I store quality slow burning carbs and proteins and it's largely digested at the start of the ride. When snacking on super long rides, I eat very little at one time (half sandwich/bar/fruit).
All of this is theoretical, not scientifically proven and assumes you have normal glucose levels and you have no illnesses.