Green tea (Camellia sinensis) contains substances called catechins that kill the bacteria in your mouth that turn sugar into plaque (a sticky mass of bacteria, sugars, proteins, and fats that produces cavity-causing acid when it comes in contact with sugary or starchy foods). Catechins also wipe out the bacteria that cause bad breath. Try This: Drink 2 to 5 cups of green tea (regular or decaffeinated) a day, says Mindy Green, director of research at the Herb Research Foundation in Boulder, Colo. Consider making a thermos of green tea to drink at work. The night before, steep 3 to 4 green tea bags in 4 cups of boiling-hot water in a covered thermos for three to five minutes. Remove the bags. Serve the tea the next day over ice or after reheating it.