Nicotine gum while fasting

I have been a heavy smoker for yrs and quit cigarettes about 3 months ago & use nicotine gum 4mg & chewing gum.
Will this ruin a Water Fast ? I dont want to have a mental breakdown from nicotine withdraw but I dont want to trigger my digestive system by chewing. Can you give me advice?
Also is herbal tea, stevia or decaffeinated black coffee a bad idea? I'm 130 lb ,31 yrs old, female , 5'4 & want to fast 30-40 days.
Also is going past 30 dangerous because of my size ?
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