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October 12, 2021

Is the 'diet' in diet drinks a 'false promise?' Here's what one study suggests.

Daily Briefing
    Editor's note: This popular story from the Daily Briefing's archives was republished on Oct. 20, 2022.

    The artificial sweeteners used in diet drinks may stimulate the appetite and cause increased cravings—especially for women and people with obesity, according to a study published in JAMA Network Open.

    Want to help your patients lose weight? 3 reasons why commercial diet programs alone won't cut it.

    Study details

    For the study, researchers conducted a randomized crossover trial involving 74 participants over the course of three visits to determine if higher BMI and female sex are associated with increased brain reward activity or hunger response.

    All participants were right-handed, nonsmokers, non-dieters, not taking medication, had a stable body weight for at least three months, and had no history of eating disorders, illicit drug use, or medical diagnoses. In addition, 58% of study participants were women. The average age of participants was 23.40 years old, and the BMI range was 19.18-40.27.

    Notably, according to the study, most previous research on diet soda has focused mainly on males and people of normal weight.

    As part of the randomized crossover design, participants consumed drinks containing sucrose, sucralose, or water. Then, the researchers measured the participants' responses to diet soda three ways, including:

    • Taking MRI brain images of the participants to record the activation of parts of the brain that are linked to cravings and appetite increase;
    • Taking blood samples from the participants to measure blood sugar and hunger-driving metabolic hormones; and
    • Tracking how much each participant consumed at a buffet table at the end of each study visit.

    Key findings

    According to Katie Page, a physician specializing in obesity at the University of Southern California and co-author of the study, the results showed that "females and people with obesity had greater brain reward activity" after they consumed the artificial sweetener.

    Both females and people with obesity also experienced a reduction in the hormone that inhibits appetite—and they consumed more food after they had drinks with artificial sweeteners, compared with after they had drinks with sugar.

    In comparison, male participants and people of healthy weight didn't experience an increase in brain reward activity or hunger response, which the researchers said suggests they aren't affected in the same way.

    "I think what was most surprising was the impact of body weight and biological sex," Page said. "They were very important factors in the way that the brain responded to the artificial sweetener."

    Study sheds light on artificial sweetener debate

    While some previous studies have shown benefits of artificially sweetened beverages, long-term research suggests that diet soda consumption is linked to increased weight gain—and experts said the latest study should shed some light on this "false promise," NPR's "Shots" reports.

    "This study offers some clues as to why," Laura Schmidt, a professor of health policy at the University of California, San Francisco, said. "Artificial sweeteners could be priming the brains of people with obesity to crave high-calorie foods," thereby disadvantaging people who may benefit most from a lower-calorie diet.

    According to NPR's "Shots," one hypothesis as to why this disconnect occurs posits that the body may be confused by artificial sweeteners, making it believe sugar is coming.

    As Susan Swithers, a behavioral scientist at Purdue University who was not involved in the study, put it, we're "supposed to get sugar after something tastes sweet. [Our bodies have] been conditioned to that." As a result, when we consume artificial sweeteners and the sugar never comes, our body's anticipatory responses are confused—which could throw off our ability to efficiently metabolize sugar that we consume later.

    If this consistently happens to individuals who drink diet soda, it could increase the risk of Type 2 diabetes because when blood sugar rises, so does the body's insulin levels, Swithers added. "So what you're doing is you are kind of pushing the system harder," she said.

    Given the results from this new research, Schmidt suggested, "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." (Aubrey, "Shots," NPR, 10/7; Yunker et al., JAMA Network Open, 9/28)

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