he question: A few weeks ago, Beyoncé ignited a minor firestorm in the health community when she inked a deal with Pepsi for a multimillion-dollar ad campaign that includes a limited edition soda can with her face on it and a performance at the Super Bowl halftime show. Mark Bittman at the New York Times called it an "odd move for a politically aware woman" known for her connection to the Obamas, especially since the first lady's primary initiative concerns combating childhood obesity. As Bittman puts it, Mrs. Shawn Carter "is renting her image to a product that may one day be ranked with cigarettes as a killer we were too slow to rein in." And that may well be the case: According to new research, the sugary beverage's effect may go beyond your waistline, also affecting the brain. More specifically, researchers asked: Is there a link between drinking soda and diseases like depression?

How it was tested: 263,925 adults were evaluated from 1995 to 1996. Their drinking habits were closely monitored — stuff like soda, tea, fruit punch, and coffee. About a decade later, researchers asked whether any of the participants had been diagnosed with depression since the year 2000.

The outcome: About 11,311 people said they were clinically depressed at some point. Subjects who routinely consumed soda (for this study's purposes, four or more cans a day) were 30 percent more likely to develop depression than people who didn't drink any. Strangely, it didn't matter if the depressed drank the regular variety made with high-fructose corn syrup or diet soda. On the bright side, coffee drinkers were slightly less susceptible to depression, demonstrating a 10 percent lower likelihood of encountering the disease. 

Why this could be: The study only found an association between soda and depression, but didn't investigate the link any further. They did, however, suggest that coffee's anti-depressant properties might have something to do with caffeine, which is a noted brain stimulant. 

What experts say: Study author Dr. Honglei Chen of the National Institute of Environmental Health Services: "Our research suggests that cutting out or down on sweetened diet drinks or replacing them with unsweetened coffee may naturally help lower your depression risk."