I weighed 253 about 4 months ago and started biking. Lost a little weight, but not what was expected. Since then, I started watching what I eat and have lost 35# so far with about 50# to go.
First, I limit what I eat to about 1500 calories (I'm a woman - you'd need more). I bike 12 to 15 miles a day, 5 days a week and 20 - 30 miles on Sundays. Monday is a rest day. The weight is really coming off now.
Someone on this forum mentioned
http://www.fitday.com/. They have a website where you can enter your food intake and exercise and view some pretty cool statistics about what you've eaten and how you've exercised. After looking at the website, I went ahead and purchased their stand-alone program for the PC. It is really a BIG HELP in tracking the food I'm eating and energy expended. Plus... with the graphs, it's really motivating to see the weight graph going down and the miles graph going up!!!
In any case, log what you eat every day and calculate how many calories you're eating. The bottom line is you can't loose weight if you're eating more calories than you're expending.