it sounds as if he has decided to combine keto with mounjaro or some kind of fad like that. Or he is seriously restricting his calories?
Root veg are quite high in carbs, so thats probably something to do with it. Is he mainlining suplliments?
Id be worried that its not sustainable. I think for me, as Im not going for massive fast loss (I want my 60 year old skin to be able to keep up with it all as best as it can) Im trying to learn what a healthy amount of food looks like, so that when I come outt the other side I am able to hopefully maintain without too much difficulty. This is a lifelong change, not a quick fix race to goal. His body wont survive without carbs longterm, and then he wont know how to eat properly.
I use the Nutricheck app to log my meals - you can tell it what kind of diet you are on, and Ive set mine to GLP-1. It gives me a daily target of protein, calories and carbs. Im on 1200 calories, with aiming for 115.5 gm protein (I rarely manage that) and 63 gm carbs.
Being in ketosis due to carbs below, I believe, 30 or maybe even 20, is quite a strain on the kidneys, and add to that metabolising the mounjaro too.
have a google of 'can ketosis on mounjaro cause mood swings and why'