https://link.springer.com/article/10.1007/s00125-018-4732-x

So you what is stated in this publication is true during the next 10 years after weight loss, but false after.

Anyway weight loss involves having a change of life style, so why bother if those cells are still there if the weight goal is reached?

1) Fat cells are strongly conserved.

Your body "knows" how many fat cells it has and will replace them if you try to get rid of them.

This has the effect that liposuction doesn't work for weight loss. Your body simply puts the removed fat cells back somewhere else. There are studies about this.

My suspicion is that they are strongly conserved over the short term but over the long term can be adjusted. The body almost never supports an excess in something it doesn't need if it can get rid of it. However, there are no medical studies about this and they would be fairly difficult to carry out.

2) Fat cells absolutely get replaced. They have a half-life of somewhere between 2-3 years.

3) Fat cells "remember" the local chemical environment when created.

This means that fat cells "remember" your weight. This is one of the many mechanisms which fight you when you lose weight. It's why you have to maintain lower weight to get your setpoint moved down.

hmm by that logic people should not become obese to begin with if people are born not obese

For most people, what you said is true. As they gain weight their baseline appetite does decrease.

The issue is that humans have lots of mechanisms to encourage eating more (for example: eating is generally pleasant--most people like a nice dessert even if they are full) and not a lot of mechanisms to encourage eating less.

https://www.pnas.org/doi/10.1073/pnas.95.24.14168 (Insulin depletion triggers death of fat cells.)

Apoptosis of fat cells is a popular outpatient procedure (see, e.g., Coolsculpt).

Hell, another study, on humans, even notes that fat cell death is actually more prevalent among the obese than the lean (https://www.medicalnewstoday.com/articles/318927#Beyond-canc...).

I would suggest that the practical solution is to prioritize exercise and food selection rather than calorie restriction.

It may be the case that some people need to eat a lot more to feel normal. Okay, fine, then they also need to exercise a lot more to be healthy. This is inordinately common among world-class athletes by their own admission, and it often shows up in their less-active retirement. So maybe you need to eat 6000 calories a day to feel normal. Okay, fine, do that, and actually put in the work to burn off the excess. Should be about 8 hours, and you’ll be a personal hero of mine at the end of a month of that.

I think most people would be a lot better-off if they would ignore the scale and focus only on performance, but be honest about it. For instance, I don’t care how much you weigh, but if you can’t run a mile in under 10 minutes and pick your own body weight off the floor, you’re going to have problems. Focus on improving a broad range of physical ability, eat as much as you need to keep improving, and you’ll be a lot better off in the long term.