In spite of  regular brushing if there is bad smell while breathing than the reason behind this is indigestion, constipation of starch and sugar in food, smoking, dry mouth, gas, acidity, or diabetes. Swollen gums also give birth to bad smell. To prevent it drink at least 10 - 12 glasses of water in the day and chew peppermint and cardamom.  Besides this  eat fibred  grain like bajra,  millet.  Increase the consumption  of fruits and vegetables.  Vitamin B can also be taken as supplement along with Zinc and magnesium.