This guy claims that Lithium may be partially responsible for some weight gain in our population, but also, that desalination plants cause extra lithium as well.
If it was mined out, that would be viable, but if not...
And despite the initially valid-seeming high hopes for their amazing scholarship, currently it looks that they are too crackpot-y :/
https://www.lesswrong.com/posts/7iAABhWpcGeP5e6SB/it-s-proba...
https://www.lesswrong.com/posts/NRrbJJWnaSorrqvtZ/on-not-get...
Will the contaminant hypothesis of modern obesity be judged true by expert consensus before 2032? 8% yes 92% no