I once made a few observations (nothing really scientific ) all things being equal i.e. no extra increase in calorie input, I reckoned on losing 1lb of body fat per 360 miles or so, this is loosely based on 25% of calories used are fat calories and approx 40cals/mile so 40*0.25=10 3500(fat cals to lose 1lb)/10=350 miles, like I said not scientifically proven, other factors play apart also.
I think its possibly why many start cycling to help lose weight then give up as nothing seems to be happening and its fing hard to start with.