It kind of depends on your current state of fitness. Some people loose 5 pounds but gain 2 pounds of muscle. Most that are far far out of shape can't stick to cycling for fitness .... either their body hurts, have no time, or some other reason. If one wants to you will find a way, those that that truly don't want to will find an excuse (not just cycling).
Lots of factors go into weight control. Some say it is a simple equation, calories consumed vs. calories burned. I tend to say cut out the sugary drinks, minimize alcohol consumption, and reduce/minimize consumption of enriched bread products. Your body will balance carbs, fat, and triglycerides beyond this (with some activity).
My weight is steady but I ride 3,000 miles a year for 6 years now. Find a group, friends, or co-workers to ride with regularly. This will reduce procrastination. Incorporate riding to work once or twice a week. First ride from work to home at the end of the day then into work the next day (because you have to, no car). This lets you clean up at home and then in the morning you will not work up a big sweat on the return trip. After a few times it becomes habit and confidence is there to figure other stuff out. Of course lets hear the excuses 1) I can't leave my car 2) I need my car 3) there is no where to clean up or change at work 4) its too far. Like I said if you truly don't want to one will find an excuse.