Saying that diet's or healthy lifestyles don't make fat people thin and stay that way, is not the same as saying that it is impossible to lose weight. How can it be impossible to lose weight? How can a body maintain its energy flow if weight stores can't be used up?
The daily variance in our weight shows that we are always losing and gaining weight as part of the normal process of maintaining a supply of energy that sustains life. Something very freaky would have to be going on for those fluctuations not to occur at all. The issue is not can weight be lost, or can it be "kept off", that is not in doubt.
The questions is by what route?
The route widely thought to be the only one, restricting energy through intake and expenditure, ignores that the body is designed to restore balance. This means trying to restore any loss brought about by calorie restriction. Whatever weight one loses or maintains reflects the inefficiency or inability of that body to achieve that balance before you lose weight.
Given enough time, it tends to catch up with itself.
Imagine juggling a load of objects and then being given more and more until you drop the lot. The weight loss dieting equation's a bit like that. When you start "dropping things", you rebound. The whole obstacle course of a diet-the planning, weighing and measuring, extreme conscious watchfulness, endless calculation etc., is exhausting.
In other words the weight you lose is your (body's) failure and your inability to lose weight/get thin is its successful defence of the status quo as it is programmed to.
I have absolutely no doubt that it is possible not only to lose weight, but that it should be possible to as easy as it tends to be gained. Why not?
On the whole weight gain is spontaneous, whatever you think has caused it to occur/identify as its cause, is usually just the playing out of some cause or other. Cause may be important, but I think it should be possible to reverse weight, in at least some cases without knowing what that is.
Gaining weight/becoming fat is about some rubicon being crossed some upward pressure causing a giving way. Whatever prevents that beforehand stops occurring to the extent that prevents that (new) accumulation of fat cells and tissue.
And so on, either your body stabilises there or the process continues.
Nor should it hurt. The assumption that pain is what stops weight loss misses the point. That comes from the action of your body's defence of itself and the effects of calorie restriction.
When your body let's go of weight as a side effect of changes in your life, or using up the energy calories
Pain is a sign of the unnatural nature of imposing a famine on yourself.