Andrew Huberman recently had a Harvard educated psychiatrist on the podcast. This psychiatrist specialized in treatment resistant mental health conditions. He was trying to help a patient lose weight and inadvertently found it helped their psychiatric symptoms as well. Fast forward 5 years and he had written a book, and the tl;dr is that he has seen many patients improve their conditions be going low / no carb. For patients with less extreme disease they can often get by with low carb and eliminate fructose but keep some healthy complex carbs in their diets. Seriously ill patients may benefit more from full ketosis. In any case, he often reports patients are able to reduce or sometimes eliminate medications on this diet which helps when they have trouble with the side effect profiles.