The main article is paywalled and appears to be a layman's translation. The first reference (visible in the preview) looks like the biologists' version. https://www.nature.com/articles/s41586-024-08165-7
I.e. human and mouse fat cells epigenetically change in response to weight gain*, they don't change back in response to weight loss, and in the mouse case they demonstrated that the mice with the changes gained the weight back faster.
I would (naively) expect this to also be true in humans, which would explain why rebound weight gain is incredibly common.
I personally see this as significant because it's evidence that obese people and formerly obese people are directly going to have more trouble getting thin, at the level of cell biology, than people who were always thin.
*The abstract implies this about human cells but doesn't explicitly say so. I presume it's a known fact about human fat cells.
From what I came to understand fat cells never really die but lie in wait to do their given job. Now they need to find out why in some people as they age, the fat cells around the gut fights harder to keep it.
[1] https://www.smithsonianmag.com/smart-news/fat-cells-retain-a...
[2] https://www.livescience.com/health/fat-cells-have-a-memory-o...