Lithium and weight loss assoc with chemotherapy

I know, we normally talk about lithium causing weight gain. Hence, I can’t find much information to help my query so I’m purely going on first principles. I’m hoping someone might have some clinical experience in this area they’d be willing to share…

I’m working through another case from my interview study and it’s making me think about the pharmacology. A woman in her forties who has a history of bipolar disorder and schizophrenia, stably managed on clozapine, lithium and venlafaxine.

She experiences a rapid weight loss following initation of her chemotherapy (153kg to 123kg). Her diet changes over this time too, to something that is possibly quite high in salt:

I live on quick and easy meals. Eggs on toast, you know your Heinz canned dinners, you know you get beef hotpot, beef and vegetables, yeah. Or spaghetti on toast, or scrambled eggs, you know

Higher salt intake would possibly reduce lithium level, while weight loss would likely increase - is that right?

Would this weight change be significant enough to impact her lithium levels?
(That’s a genuine question, I don’t know)

Note that she was experiencing many generalised symptoms that in normal circumstances (i.e. not someone who’s been receiving chemo and radiotherapy) might be considered signs of mild lithium toxicity e.g. nausea, vomiting, muscle weakness, drowsiness, apathy, flu-like illness