Pumpkin seeds are high in trptophan, which i believe boosts serotonin. Obviously not on your fast, but look into natural ways of boosting levels to help with smoking withdrawal symptoms.
Look into animoacids, such as l-theanine, also in green tea and pharmagaba, a natural gaba that does cross the blood brain barrier, for your anxiety, depression? and there is lots of other stuff to try, safer than prescription drugs and non adictive. Not on fast though, I was also told that fasting balances your brain chemistry.