Next to water, tea is one of the most popular beverages in the world, and at just a couple of calories per serving, it's loaded with flavonoids that make it one of the world's healthiest beverages as well.

"There are really only three drinks that I ever recommend humans consume," said Dr. Andrew Freeman, director of clinical cardiology and cardiovascular prevention and wellness at National Jewish Health in Denver. "The best is water, and next would be unsweetened tea and unsweetened coffee. Everything else, unfortunately, doesn't really have any benefit, and many (when laden with sugar) cause...