In the past year and a half I have lost 40 lbs and several inches, even my feet seem to be smaller. I am predisposed to obeseity and lost my father at 59 due to multiple problems including type 2 diabetes. I digress.
I have changed my lifestyle during this time, going from working at a carwash to being back in a bike shop. The job market here is bad but, the best times I've ever had was working in a shop. I've not done much to change my diet other than cut out most sweets type stuffs and processed snacks. I drink plenty of water, mostly carbonated flavoured kind with 0 calories, with the occasional cola or tea. I try to eat handfulls of dried fruits and nuts for intermitant snacks instead of chips etc. Really very little change.
The big change came simply from riding. I live 6 miles from work and we ride 23 miles every morning, then I usually ride home. Add these to longer weekend rides and I'm doing 300 miles a week, which is 40 miles a day, or 12 hours a week. This is way doable for anyone, in my opinion. Most people watch tv or play on the interwebs that much when they could be riding (me included).
So to finally answer your initial question, that just seems like a way bad way to lose weight, even for the morbidly obese.
btw- One can have other problems creep up when doing even moderate loss. Acustomer that I personally sold two bike to this year recently came in to check in, sort of. I didn't realize we had not seen him since May or so, he had a stroke in June. He was losing weight, gaining fitness and rewarding himself but, he had already created health risks that he didn't know about yet. Now he has it all under control and has had to to a break from riding and will be back later for a road bike.