As others have suggested, cycling can only do so much for you if you're unwilling to modify your diet. Endurance activities are tough in that you generally have to eat something before and during in order to fuel them. Plus, they tend to enhance your appetite. So, finding that balance can be tricky for some. I, personally, have mostly maintained my weight through cycling and my other activities. I've lost a few (and gained a few) pounds, but that's about it. I am absolutely ravenous most of the time when I up my mileage. From that standpoint, I actually think shorter, more intense rides are better for weight loss. Still, it's all about calories in versus calories out. There's no magic bullet.

I would strongly urge you to get engaged in a variety of activites in addition to cycling: walking (or running) hiking, kayaking, Pilates, yoga, strength training. Especially if you're worried about whole-body muscle development, it's good to balance cycling with other pursuits. Balance and flexibility are also important.

Good luck!