First of all your breath is supposed to be foul when fasting, this is a sign of toxins coming out. This also occurs every night when you are asleep. This is why one should use a tongue scraper every morning after waking up and after brushing your teeth.
A few reasons our breath chronically smells are mainly when our stomach has food fermenting, our nasal cavity is not clean and we have a tooth decay.
During fasting more toxins means more bad breath.
Please do not use any products for cleaning your mouth except hydrogen peroxide and scraping your tongue, no baking soda and definitely no lysine.
Clean your liver and colon to have a clean digestive tract and you will see that you do not have bad breath.