Green Tea: The catechins and other plant-based compounds in green tea may be linked to helping prevent colds and influenza. A study published in the Journal of the American College of Nutrition found that consuming green tea increased immune cells, boosting their ability to fight an affront to the system. In theory, that may translate to fewer colds and flu, says naturopathic physician Paul Anderson of Seattle’s Bastyr University. And if you get a cold, “it may be less severe,” he adds. The catch: “You’d need to drink at least eight to 10 cups a day of green tea,” Anderson says, to match the antioxidant amounts used in studies. If nothing else, green tea doesn’t seem to hurt, and a cup of hot tea contributes to your daily fluid needs.