From March until September this year I did 1608.69 miles on my bike including two 100 mile rides and guess what I did not lose a single pound, so from the end of September I decided to look at what I was eating. I use this website ->
http://www.weightlossresources.co.uk to track what I eat and the exercise I take and I then know when I am eating more or less calories than I should. Of course there are many other ways of logging our intake but that one works for me. The fact is most people have no idea what there daily calorie intake should be or if they are exceeding it or not.
Since I started watching what I eat I have gone from 13 stone 3 to 12 stone 4 in 2 months I still go out on the bike and my mileage from March is now up to 2,396.08 and I am getting fitter and faster all the time and I can now get into a proper cycling jacket without looking like I am trying to smuggle a small primate inside it, but the point is without regulating what you are putting in your mouth, and finding out what your daily intake should be and what your daily intake actually is you will never lose weight, cycling will help and will keep you fit but it will not make you lose weight if you are eating more than you are burning off.
Some of the other things I did that also helped are giving up the following:
Chocolate Bars
Alcohol
Caffine
Junk Food
Take Aways (except the odd one every couple of weeks)
and I started eating alot of fruit and veg and salads and trying to have 3 meals a day (including breakfast) at a regular time everyday and it works for me.