Think you're making a healthier choice when you reach for diet soda instead of a sugary soft drink? Think again.

Diet soft drinks may have minimal calories, but they can still have a major impact on your waistline, according to two studies presented at a meeting of the American Diabetes Association in San Diego.

Researchers at the Texas Health Science Center at San Antonio tracked 474 people, all 65 to 74 years old, for nearly a decade, measuring the subjects' height, weight, waist circumference, and diet soft drink intake every 3.6 years. The waists of those who drank diet soft drinks grew 70 percent more than those who avoided the artificially sweetened stuff; people who drank two or more servings a day had waist-circumference increases that were five times larger than non-diet-soda consumers.