[bumby]

You cut out the part that said the diets improved people’s health at 6 mo. But they were hard to maintain for 12 months. I think a lack of consistency is the issue. From your link:

>What if they'd lasted 12 months, or two years, or a lifetime? The benefit would likely have been greater and more long-lasting. The trick is to pick a diet with foods you actually like so that it's not so hard to stick with it.

Meaningful behavioral change is hard, especially in a modern food environment.

[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...)