Glad to see that you understand that WEIGHT is NOT equal to FITNESS. As a matter of fact when most people begin any physical fitness program they tend to gain weight. Lean muscle weighs more that fat and as you start building muscle mass you body will retain more fluids to help nourish the new muscle you build.
Bicycling is a great method of weight loss as it requires you to use the largest ( and most metabolicaly active) muscles in your body.
I would suggest, from personal experience, that you invest in a heart rate monitor. When you exercise at a heart rate of 60-70% of your (Theoretical) Maximum Heart Rate, you are in the correct "zone' for burning body fat and building muscular and cardio endurance. The reason I suggest you use a monitor is that I believe that most will ride at a higher heart rate which, if you are riding for longer periods ( 90 min). may actually break down muscle tissue for fuel. The less muscle mass = less energy expended throughout the rest of your day.
Of course this is just general information. I would always suggest you educate yourself about how the body works, On-line resources are great, but a Nutritionist and/or Personal trainer ( SHAMLESS SELF-PROMOTION ) can condense all the information out there down to bite size chunks that may be easier for you to swallow.
So keep up the good fight and happy trails

Captain Chaen