> If you change your lifestyle temporarily, the effects are temporary.

Not quite.

If the lifestyle deteriorates, then weight regain is expected. However, people might regain only a fraction of the weight lost. It is possible for some of the weight loss to be permanent.

Also, even temporary changes in lifestyle can produce benefits that outlast the intervention, like lower risk of disease such as diabetes. Exercise is notable for providing numerous benefits that persist even if weight is completely unmodified.

> If you change your lifestyle permanently, the effects are permanent.

No. It improves your odds of success, but does not guarantee it.

Body adapts significantly over time when subjected to weight loss. There are compensatory physiological adaptations that favor weight regain, such as changes in energy expenditure and appetite. Even with sustained effort, maintaining the initial weight loss may become progressively more difficult because of those changes. This shows up in research as results like mean weight loss of ~9% at year 1 and ~5% at year 8.

Sad reality is, very few people have the resolve to do permanent changes to their behavior, the older the worse. Too deep in their comfort zone without even realizing this, even with looming heart attack or other massive health issues. Its much easier to end up seeing a grown man crying about how he has to eat that next snickers bar rather than sustaining resolve with some healthy trend.

For the love of god or any other deity I can't grasp this, its trivial for me to muster a tiny fraction of discipline and simply change direction from now on. But people out there are vastly different than me, thats pretty obvious, ie many people detest sports or even sweating. Addictions, and over-eating is an addiction (or some form of stress-coping mechanism) have a way to grasp core of one's existence and not let go.

My wife sees such overweight folks with not-so-much-time-remaining-on-earth as GP regularly. As she says - they basically over-ate themselves into mental disorder (or started with it and their body over time aligned with behavior). To actually fix this, that mental disorder needs to be tackled, no gastric operations or wegovy injections provide permanent solution. But they sure make pharma companies richer and give this warm fuzzy feeling of achieving actually something visible, even if temporary.