One reason not mentioned, and not tracked on labels, is life energy. This is accounted for in some systems that recommend eating fresh, raw, wholesome ingredients. In general, eating foods which are alive (like yogurt or fresh-picked berries) or very recently alive (fresh potatoes that are boiled, or a lobster taken from a tank and slain just before it it hits your plate) give you more life energy than things which have been dead a long time. The less messed-with, the more life energy; the more processed, the less life energy. Also foods raised with joy and verve have much more life energy than those raised in desolate conditions. So organic, pastured, wildcrafted, etc. tends to be more nourishing than factory-farmed stuff.
Going a step further, you can capitalize on the benefits of growing or at least picking some of your own food. This can be a challenge for people with mental illness. However, depression and activity don't like to live together! Getting outside in the sunshine and fresh air is good for mental health; so are walking around and doing practical tasks. Even if all you do is pick enough apples for the next few days, you're ahead of the game compared to buying a jar of applesauce at the store.