Let’s face it: No one drinks diet soda for the taste. People drink diet soda in the hopes that it will help them lose weight—or at least keep them from gaining it.
Yet it seems to have exactly the reverse effect, according to new studies presented this week at the American Diabetes Association’s Scientific Sessions in San Diego.
Study subjects who drank two or more diet sodas a day had waist size increases that were six times greater than those of people who didn’t drink diet soda, said researchers from the University of Texas Health Science Center at San Antonio.
“What we saw was that the more diet sodas a person drinks, the more weight they were likely to gain,” said epidemiologist Sharon Fowler of the University of Texas Health Science Center.
The study was based on data from 474 participants in a larger, ongoing research project called the San Antonio Longitudinal Study of Aging. In that study, the participants were followed for nearly 10 years.
While the findings were surprising, they also offer some explanations.
Nutritionist Melainie Rogers, who works with obese patients in New York, has found that when patients are switched from regular to diet soda, they don’t get slimmer. “We weren’t seeing weight loss necessarily, and that was confusing to us,” said Rogers.
So why would diet soda cause weight gain? No one knows for sure yet, but it could be that people think they can eat more if they drink diet soda, and so overcompensate for the missing calories.
A related study found the sweetener aspartame raised blood sugar levels in diabetes-prone mice.
“Data from this and other prospective studies suggest that the promotion of diet sodas and artificial sweeteners as healthy alternatives may be ill-advised,” said study researcher Helen P. Hazuda, professor at the University of Texas’s school of medicine. “They may be free of calories, but not of consequences.”