In one study, scientists at the University of Texas Health Science Center monitored 475 adults for 10 years, and found that those who drank diet soda experienced a 70% increase in waist circumference over the period, compared to those who abstained from the sugary drinks. For those who drank more than two diet sodas a day, they saw a 500% increase in waist expansion! They believe these results are due to the fact that aspartame raises blood glucose levels, and when there is excess glucose in the blood, it’s stored as fat.