I've lost two stone and working on my third by cycling my ass off and doing crunches while I ride. I try to ride about 30 kms every second day (weather permitting) at about 30kph for one hour. burns between 1100 and 1200 calories. I ride a fixed gear track bike on flat road with cycling lanes. I put my head down and hit it hard.

I limit my calories to +1700 per day. That means it I burn 1000 calories cycling I eat 2700 calories that day.

"Lose It" is a little iPhone app I use to track my caloric intake. Works a charm. Flat stomachs come from keeping the muscles happy and the body fat down. Not rocket science.