We now have FDA-approved GLP-1 receptor agonists like Semaglutide that produce sustained weight loss of a magnitude similar to the weight gain discussed in that article. So the idea that something similar could be messing with this or a similar pathway hardly seems shocking to me, even if lithium perhaps isn’t the culprit.

(As an aside: we’ve also learned that proteins produced by certain gut bacteria have a similar effect on the same pathway, so it’s not crazy to imagine that gut dysbiosis could have an effect on weight gain. https://www.nature.com/articles/s41564-021-00880-5)