And here's the problem with that.....with just diet you start to basically starve yourself and your body slows down even further because it doesn't know why it is suddenly being deprived of the calories it's used to.

So what happens is you lose weight initially, maybe a good amount but you'll plateau, stop losing and maybe even gain a few back and not know why........then the diet will be abandoned, the old caloric intake will be resumed and because the metabolism is at a slower rate due to diet alone the person will generally gain back all the weight and THEN SOME.
Yo-yo dieting.
Sustained weight loss without exercise AND sensible diet is a waste of time at leastfor a truly overweight person who has struggled with weight for long periods of time.

A person losing another couple vanity pounds whois blessed with higher metabolisms or are athletic to begin with is another story and can just diet it off.

Trust me dude, this is what I went to school for.......Athletic Training Health Science.