There is no doubt that tea is one of the best drinks on the planet. After all, it has almost no calories and lots of potentially healthful antioxidants. So drink up. But also realize that plenty of research is still to be done. Here is the scientific scoop on five of the most popular brews.

Green Population studies have found a link between green tea consumption and lower rates of heart disease. Next up: Clinical trials are needed to determine if it is truly a cause and effect.

Mate One human study found that a pill containing concentrated yerba mate, guarana, and rosemary reduced appetite, but there is no evidence yet that drinking mate can replicate the effect.

Black There is conflicting evidence as to whether drinking black tea truly wards off heart disease and cancer, but test-tube studies suggest that it contains compounds that help fight both maladies.

Chamomile The American Academy of Sleep Medicine found little evidence that chamomile helps you fall asleep, as is often claimed. But one study found that its extract may have anticancer properties.

Rooibos Some animal research suggests that this South African tea may provide many health benefits, such as boosting immunity. Large human studies have yet to be conducted. [source: Men's Health]