Caffeine gets both a good and a bad rap. When it comes to boosting your metabolism, it may help to brew up a pot of coffee. Caffeine is a stimulant, and many people find that it improves their alertness -- that's caffeine's affect on the central nervous system. Stimulants rev your engine, and that includes boosting your metabolism.
In addition, studies have found that green tea may boost your metabolism and help you lose or maintain weight, especially when combined with caffeine. Researchers at the Lausanne University in Switzerland found that study participants who drank three servings of green tea over a span of three days saw a 4.6 percent increase in their energy expenditure -- and that equals a boost in metabolism [source: University of Maryland].