Simonfbarns – thats very interesting. I shall mention it to the fat fcukers in my office who stuff their faces all day.
I know what you mean about mountain biking making you hungry. You have to watch out for that, but you can stuff yourself with not fattening foods post ride.
Mtbing is more fun than say running or road riding so at least the excersice is fun meaning your more likely to keep it up.
In the long run, so long as your riding and having fun and not eating shite you will get fitter and lose weight.