I also noticed fasting helps with ADD, depression, lack of energy and "mental energy", lack of ambition, so called "brainfog". I noticed it when I had the flu a few months ago, and all I ate was water and tomato soup. If you like tomato soup, maybe it will work for you, especially fresh cooked tomato soup. You can probably find a good recipe on recipesource.com.
For a less drastic fast, I've eat nothing but fruits and vegetables for a few days, then gradually add more foods and try to replace the bad foods with better ones while I'm not depressed and have the focus to do it.