Contrary to popular marketing, you can gain weight drinking diet sodas. In fact, a new study shows that men and women who consumed diet drinks saw their waist sizes expand 70 percent more than study participants who avoided diet drinks. Researchers from the University of Texas Health Science Center at San Antonio followed 474 men and women ages 65 to 74 for almost 10 years. During that time, they found that those who consumed two or more diet sodas a day increased their waist circumferences five times more those of the other study participants. The explanation may be related to findings from another study, in which laboratory mice ate a diet containing the artificial sweetener aspartame, while mice in another group consumed their regular food. After three months, the mice in the aspartame group had higher blood sugar levels than those in the other group. Researchers speculated that artificial sweeteners may trigger appetite but don't provide calories to satisfy the craving, or that the sweeteners could inhibit brain cells that make you feel full, thus prompting more eating.