Think again.
http://www.nejm.org/doi/full/10.1056/NEJMoa1105816
"One year after initial weight reduction, levels of the circulating mediators of appetite that encourage weight regain after diet-induced weight loss do not revert to the levels recorded before weight loss. "
and
"The evidence presented in this paper provides novel insights into the nature of weight loss and associated compensatory changes. Further, it suggests that multiple redundant mechanisms have evolved to maintain body weight and thereby counteract a reduction in caloric intake. This redundancy may in part explain the high degree of failure and weight regain observed following weight loss through lifestyle intervention [20]. In this context, it is noteworthy that low-dose leptin replacement monotherapy has been shown to reverse many of the neurologic, hormonal, and behavioral adaptations that promote weight regain, despite the heterogeneous etiologies underlying weight regain [9294]. "
It's basically a fact that permanent alterations in physiology once obesity has been sustained make it extremely difficult to lose weight and maintain a normal weight. You can't just delete 80 billion extra fat cells and you can't restore neurons involved in appetite regulation that have been damaged by inflammatory processes that accompany obesity. Saying that these changes alterations aren't permanent in a vast majority of obese people is like saying that global warming isn't happening or evolution isn't real.
I'll let Rudolph Leibel, one of the top obesity researchers in the world, explain:
https://www.youtube.com/watch?v=2i_cmltmQ6A