[verteu]

I think metabolic adaptation plays a larger role. In this Biggest Loser followup study, even after six years (!), participants' resting metabolism burned 20% fewer calories than a "typical person of their current weight":

https://pmc.ncbi.nlm.nih.gov/articles/PMC4989512/#:~:text=co...

> In contrast, a matched group of Roux-en-Y gastric bypass surgery patients who experienced significant metabolic adaptation 6 months after the surgery had no detectable metabolic adaptation after 1 year despite continued weight loss (17). It is intriguing to speculate that the lack of long-term metabolic adaptation following bariatric surgery may reflect a permanent resetting of the body weight set-point (18).

[verteu]

Update: I also found a dissenting letter, with some references: https://www.ejinme.com/article/S0953-6205(21)00241-7/pdf

"Metabolic adaptation is not a major barrier to weight-loss maintenance" (https://www.sciencedirect.com/science/article/pii/S000291652...)