Many people have experienced partial or total withdrawal of symptoms like anxiety, anhedonia, brain fog, even schizophrenia and serious mental illness after removing industrially processed foods from their diet.
Some people benefit going on Macrobiotic diet, other benefit starting with raw food diet or vegetarian diet ... generally avoiding alcohol, sugar, vine vinegar, margarine, taste enhancing substances like MSG, strong spices and strong herbs like black pepper, red meat, chicken, milk products etc ...
As people are different, it is different diets that work for different people. You may try Rotation-Elimination Diet
to figure out what you react on, and then you avoid those foods.
You should know that it may take months to pint out most of the foods that affect your mood.
Some people react on fruits, on berries, on melons, on root vegetables... etc.
People are different, so if some diet helped a friend of mine, it may not help you, but you have to start observing your own diet, and you should start with Rotation-Elimination Diet
to eliminate foods that you may react on.
Some people react on nuts. Or almost all oils, so they replace oils in cooking with butter. Everyone is different.
But most people react on sugar, alcohol, vine vinegar, MSG, Margarine, food additives
so it is a safe bet to first remove those from your diet.