Nope, diet soda won't help you look better in that bathing suit this summer. In fact, regular intake of the stuff is directly linked to increased belly fat in women and men age 65 and older, finds a new study in the Journal of the American Geriatrics Society.
While diet soda has been linked to obesity in the past, this study focused on where daily drinkers gained extra fat: in widening waistlines. Researchers also suggest a range of possible reasons for how diet sodas might increase risk, beyond just increasing hunger hormones (the most commonly held assumption).
To reach their conclusion, researchers measured diet soda intake, waist circumference, height, and weight of 466 adults at study onset and at three follow-ups. The result: the increase in waist circumference among daily diet soda drinkers was more than triple that of non-drinkers. Why that's so scary: greater belly fat has been linked to a greater risk of metabolic syndrome—a combo of risk factors that may lead to high blood pressure, diabetes, heart disease, and stroke.
There are a few potential reasons diet soda could pack on belly fat, researchers say, including the sodas' acidity from the phosphoric acid used in both regular and diet soda to lend a tangy flavor and act as a preservative. "Constantly ingesting this might create an even more acidic environment in your gut than normal, which may affect biodiversity and allow some harmful strains of bacteria to thrive," says lead study author Sharon Fowler. A large French study found an increased risk of diabetes in diet soda drinkers, and among people with more acid-forming diets.
Artificial sweeteners also may play a big role, and there are a few ways in which they may exert their negative effects, says Fowler. First, artificial sweeteners may cause changes to gut bacteria, leading to the overgrowth of strains that are more efficient at getting every last calorie out of the food you eat. Second, they may mess with our ability to metabolize glucose, which can lead to insulin resistance, which in turn increases hunger. And third, there's some speculation that they mess with us neurologically, interfering with our body's signals to quit eating.
Because the belly-expanding effects of these drinks were found at such low levels—just one diet soda drink per day—it may be best to ditch the habit altogether. If you still crave that refreshing fizz, try transitioning to something like a zero-calorie seltzer (there are even naturally flavored caffeinated varieties) or naturally effervescent kombucha tea.
