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Is Diet Soda Making Us Gain Weight?

A disturbing new analysis claims that artificially sweetened drinks may encourage eating more, not less

By Gary Drevitch

Nearly three years ago, I embarked on a largely successful personal wellness campaign. With the guidance of a trainer and a nutritionist, I lost almost 50 pounds. But even as I gladly set aside pasta, French fries, bagels and M&M's for the sake of my health, I would not part with Diet Coke.

New research shows that decision may come back to haunt me and the rest of us who turn to diet soda for a zero-calorie caffeine and carbonation fix.
My nutritionist recommended I give up my two-can-a-day habit (OK, sometimes three) and maybe switch to tea. "We don't know what artificial sweeteners can do to us," she said. "So why consume them?"
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I ignored her. But, honestly, I'd been thinking about the potential risks for years. The occasional study finding a correlation between diet soda consumption and overeating always struck a nerve. Unlike water, I did not like drinking Diet Coke without eating something with it. During the year or so that I focused intensely on weight loss, that didn't seem to matter as much. My meals were small (and sometimes skipped) and my snacks were measured out in handfuls of nuts and berries.
Today, as my vigilance has flagged a bit and my weight has slowly but measurably crept back up, the Diet-Coke-and-snacking habit has become more concerning. That worry is now abetted by the new, widely publicized analysis of research published in the journal Trends in Endocrinology and Metabolism earlier this summer. That paper indicated that drinks powered by artificial sweeteners, besides raising our risk of contracting a variety of life-shortening conditions, may actually make us more likely to gain weight than lose it.

If those conclusions prove true, a fundamental reason for the existence of diet sodas (and many other low-calorie products) may prove to be an illusion.

Why We Eat More When Drinking to Lose

The body's normal response to tasting something sweet is to send out a signal that sugar and calories are incoming so hormones can be released to prepare, explained the report's lead author, Susan Swithers, a Purdue University professor of psychological sciences. This hormonal response influences our feeling of being satisfied or full.

However, that response is blunted when we eat something that tastes sweet, but doesn't introduce real sugar into the blood system. "You get that sweet taste but calories and sugar don't show up," Swithers told "Your body says, 'Wait, this isn't what I was expecting to happen' and over time you may not produce those same anticipatory responses."

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By disrupting our metabolism, then, artificial sweeteners may induce "metabolic derangements," making us more likely to overeat because we feel less full than we should. In time our bodies may no longer release the hormones needed to process sugar, at least not at the same level, Swithers told NPR.

The studies Swithers reviewed for her analysis considered the effect of sweeteners including aspartame, sucralose and saccharin. The research found that their consumption routinely led to weight gain, as well as a higher risk of type 2 diabetes, stroke, high blood pressure, heart disease and metabolic syndrome.

Findings from the long-term San Antonio Heart Study were especially compelling, identifying a strong correlation between diet soda and eventual weight gain. On average, for each daily diet soft drink study participants regularly drank, they were 65 percent more likely to become overweight over the next eight years, and 41 percent more likely to become obese.

Further National Institutes of Health-financed research on the impact of artificial sweeteners on weight and health is in the pipeline, in part because much of what we know about their effects comes from animal studies. If those analyses support Swithers' conclusions, then it may turn out that governmental interventions, like New York City Mayor Michael Bloomberg's controversial proposal to ban oversized sugar-sweetened sodas, may not go far enough. (Bloomberg's plan is now being reviewed by state courts.)


"Public health officials are rightfully concerned about the consequences of consuming sugar-sweetened beverages, such as soft drinks," she said in a statement, "but these warnings may need to be expanded to advocate limiting the intake of all sweeteners, including no-calorie sweeteners and so-called diet soft drinks."

Our psychological response to low-calorie drinks is a critical part of the equation. The message that we should not drink our calories may now have been so well-received that some of us are forgetting the basic premise that we shouldn't get too many calories from food either. Also, the weight-loss goals of diet-soda consumers may be sabotaged by internal negotiations, conscious or not, in which we allow ourselves to eat a larger hamburger or more French fries because we're having them with a Diet Coke.

"But the animal work indicates that health problems can occur even without this kind of thinking," Swithers said. "Since we don't fully understand the mechanisms, we don't really know how to reverse the consequences and that will continue to be a problem as our population ages and the rates of chronic diseases like type 2 diabetes continue to increase."

The American Beverage Association has released a statement challenging the report, arguing that "low-calorie sweeteners are some of the most studied and reviewed ingredients in the food supply today. They are safe and an effective tool in weight loss and weight management."

Other obesity experts say the research is not yet entirely convincing. While it may prove true that diet sodas do not help us lose weight, it's not clear that they hurt the cause, either. Some smaller studies have found that many people drinking diet sodas compensate for lost calories by eating more, leading to a net status quo. Others point out that many consumers don't switch to diet drinks until they already become overweight, so the drinks themselves may not be the problem.
(MORE: Why We're Addicted to Unhealthy Snacks)

Swithers, though, maintains that artificially sweetened drinks "have been given the benefit of the doubt just because they don't have any calories. The typical response has been to dismiss this from the perspective of, 'It's only people who are unhealthy or heavy who drink diet soda in the first place.'

"But when it comes to making policy decisions, it's more important than ever that the science is considered and that the public understands what the science says in order to help them make the best health decisions."

As for me, I think I've heard enough. When I hit that usual midafternoon energy slump this afternoon, I'll take a brisk walk or boil some tea. (I hope.) Diet Coke may or may not be hurting my diet goals, but it's harder than ever to believe it's helping.

Gary Drevitch was senior Web editor for Next Avenue's Caregiving and Health channels. Read More
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