While you don't consume banana leaves, any nutrients found in the leaves seep into the food, whether the food is cooked inside of the banana leaf or served on it. Banana leaves contain the antioxidant polyphenol, which can help boost your immune system. Polyphenols also have antibacterial properties, which may help to kill germs found in food. Banana leaves also have a specific type of polyphenol, called polyphenol oxidase, which can help fight free radicals.