Diet soda doesn’t exactly have a good reputation. Its sweeteners like aspartame have been linked to headaches and decreased bone density, and to developing type 2 diabetes. But now, a new study out of the University of Southern California, Los Angeles, has found that there may be another effect of drinking diet soda that you’ve probably brushed off as a rumor for years. Read on to find out what your favorite drink could be doing to your body.
You’re doing everything right: You’re eating a low-fat, low-carb diet; you’re exercising; you’ve even given up sugary sodas in exchange for diet drinks. And yet, you still can’t seem to lose weight. That may be because, according to the USC study, of said diet soda.
The research included 74 adults, all of whom were nonsmokers who had had stable weight for at least three months. Participants also had to have not been on a diet and have no history of eating disorders or substantial medical diagnoses. The group was split into two: half of participants were given sucrose-based drinks, while the other were given drinks sweetened with sucralose—a non-nutritive sweetener. Both groups were also given water as a control.
The researchers tracked appetite stimulation in three ways. They looked at MRIs to determine neural responses to cravings, assessed blood sugar and hormone levels, and tracked participants at an all-you-eat buffet two hours after drinking the sucralose or sucrose beverages.
The results showed that men tended to consume around the same amount of calories regardless of whether they drank sucrose- or sucralose-based drinks. But women, on the other hand, consumed a greater number of calories if they had consumed the sucralose drink prior to the meal.
The study found that participants who were categorized as obese also saw greater appetite stimulation.
“We found that females and people with obesity had greater brain reward activity” after consuming the drink containing artificial sweetener, study author Katie Page, MD, told NPR.
That’s because women and obese people experienced a decrease in the amount of leptin, the hormone that inhibits appetites, after drinking the sucralose beverage, Page explained. “I think what was most surprising was the impact of body weight and biological sex,” Page told the outlet. “They were very important factors in the way that the brain responded to the artificial sweetener.”
Previous studies found an “association” between drinking diet soda and weight gain, though it’s been admittedly difficult for scientists to claim a causal link between the two.
One 2015 study found an association between drinking diet sodas and increased belly fat. The San Antonio Heart Study also followed diet soda drinkers from 1979 to 1988 and found that people who drank diet soda three times a day were twice as likely to be overweight than those who did not.
What scientists do agree on is that diet sodas can confuse the body, Purdue University scientist Susan Swithers, PhD, told NPR, and they may put you at risk for developing metabolic syndrome. “You are supposed to get sugar after something tastes sweet. Your body has been conditioned to that,” Swithers explained. But when the expected sugar never arrives, your body’s overall response system gets confused.
The sweetness of diet soda makes our bodies believe that we’re drinking real sugar and consuming calories. But because diet colas don’t have any calories, the body’s insulin receptors get tricked into making more insulin. This can lead to increased blood pressure and weight gain, not to mention an increased risk for diabetes, heart disease, and stroke.
Researchers are still reticent to recommend that people avoid diet soda altogether, but Laura Schmidt, PhD, a professor of health policy at the University of California, San Francisco, told NPR that people who are having trouble losing weight might want to lay off the soda for a couple of weeks and see if it helps.
“Artificial sweeteners could be priming the brains of people with obesity to crave high-calorie foods,” she said. “People with obesity might want to completely avoid diet sodas for a couple of weeks to see if this helps to reduce cravings for high-calorie foods.”