I haven't read any studies, but I've done some thinking on nutritional substitutes for smoking. Nicotine increases endorphin release and serotonin intake into the brain. So does chocolate. So I figured that, if chocolate can mimic the chemical reaction that smoking causes, eating chocolate could be a way to get rid of cravings and still have the same feeling from smoking a cigarette. That's not tested or proven, so don't take my word on it; just an idea.
Also, fruits and vegetables, especially ones that contain anti-oxidants and amino acids speed up the detoxing process and get the bad stuff out of your system faster, so I would look into natural cleansing and detoxing processes.