It's well known to coaches and cyclists who train a lot that the time to lose weight is in the winter when we do a lot of base miles. That's because when one rides at a lower intensity, one will burn mostly fat and thus the ride makes one less hungry after. Glycogen and blood sugar remain high. The reason one sees fat cyclists who ride base is because they eat a lot more then they should for the amount of riding they do. Duh. You go out for 2 hours a day and ride base with only water and then eat your normal maintenance diet - you'll lose weight. Try that with hard efforts and well, they won't be hard.

During the summer we tend to ride a lot harder, so we have to eat on the bike or lose our glycogen and then we'll have a recovery drink etc. after, so it's much harder to lose weight then. We need to keep the calories coming in order to be able to do the next hard ride, maybe tomorrow.