Now we know why they call it diet soda: drink enough of it, and you'll have to go on a diet. A new study by researchers at the School of Medicine at The University of Texas Health Science Center San Antonio suggests that drinking diet soda can make us very very fat. Time magazine reports that scientists at the school studied data from 474 older adults in the San Antonio Longitudinal Study of Aging, looking specifically at diet soda intake, height, weight and waist circumference. They found that while everyone's waistline expanded, those who reported drinking diet soda had 70 percent greater increases in waistline growth than non-drinkers 9.5 years later. Among those who consumed two or more diet sodas a day — waistline growth was 500 percent greater than among non-drinkers. Time reports that animal studies suggest that artificial sweetener consumption may lead to greater weight gain because it triggers the body to start storing more calories as fat.