Diet and Nutrition Claims

The Claim: Diet Soda Makes You Fat


Claims that diet soda may actually promote obesity have arisen mainly from several cohort studies linking diet soda to weight gain and other risk factors for heart disease. In one study, which followed 3,700 people for seven to eight years, diet-soda drinkers who started out at normal weights were more likely to become overweight or obese than nondrinkers. The more they consumed, the more weight they gained.

Of course, this doesn't prove cause and effect. It's possible that as people start to put on pounds, they increase their intake of diet drinks.

Untangling all this requires intervention studies, and here the case loses some fizz. Such studies, in which an experimental group is fed sugar substitutes and compared to a control group, have generally failed to show that artificially sweetened foods and beverages cause weight gain. But the research hasn't conclusively demonstrated that they lead to weight loss either. Results are mixed, and some of the most frequently cited studies showing a benefit were funded by the artificial sweetener industry.

In short, it's unclear exactly how diet soda affects weight-control efforts. Still, scientists have several explanations as to why it may not help and could possibly hurt. One is the "I'll have a Big Mac, large fries, and a Diet Coke" fallacy: People may subconsciously (or consciously) assume that because they're being virtuous by drinking diet soda, it's okay to otherwise overindulge.

Another possibility is that artificial sweeteners mess with our minds. When we taste something sweet, our brains are alerted that calories are on the way. If they don't materialize because we're drinking an artificially sweetened beverage, we're driven to go seek them elsewhere. In such a way, diet sodas may prompt us to eat more.

This is just a theory, however. What we do know is that when it comes to weight, calories matter. If diet soda helps you reduce your overall caloric intake, it can be a helpful tool for shedding those unwanted pounds.

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Reprinted from Coffee Is Good for You by Robert J. Davis, PhD, by arrangement with Perigee, a member of Penguin Group (USA) Inc., Copyright (c) 2012 by Robert J. Davis, PhD, MPH

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About the Author

Robert Davis, Ph.D.

Robert J. Davis, PhD is President and Editor-in-Chief of Everwell.

An award-winning health journalist whose work has appeared on CNN, PBS, WebMD and in The Wall Street Journal, he is the author of The Healthy Skeptic: Cutting Through the Hype About Your Health and Coffee Is Good for You. He also teaches at Emory University's Rollins School of Public Health.
Davis holds a PhD in health policy from Brandeis University, where he was a Pew Fellow, a master's degree in public health from Emory, and an undergraduate degree from Princeton University.

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