Research Claims Diet Soda Is Better Than Water for Losing Weight—but Guess Who Paid for the Study

New research tastes a little like junk science.

(Photo: George Marks/Getty Images)

May 29, 2014· 2 MIN READ
Jason Best is a regular contributor to TakePart who has worked for Gourmet and the Natural Resources Defense Council.

Beware of only reading the headlines. No doubt the soda industry’s PR apparatus is swooning over all the recent media coverage on a new study that finds drinking diet soda helps dieters lose weight—after all, the industry essentially paid for it.

A research team led by Dr. Jim Hill at the University of Colorado selected a sample of 300 adults who already regularly consumed diet drinks and divided them into two groups. Both groups received intensive weigh-loss counseling and kept journals of the meals they ate. But one group was allowed to keep their diet drinks, while the other was required to switch solely to water.

The results, which were published in the journal Obesity, found that the “water group” lost, on average, nine pounds over the course of 12 weeks, while the diet-soda drinkers lost 13 pounds.

“The results, to us, were not at all surprising,” Hill tells CNN, perhaps oblivious of how unwittingly biased that sounds, given that his study was funded by the soda industry’s principal lobbying group, the American Beverage Association.

One of Hill’s colleagues and another of the study’s authors, John Peters, pretty much bend over backward defending the integrity of the results in spite of the funding source. “We responded to a [request for proposal] that was put out by the ABA to the scientific community,” Peters tells NPR. The story goes on to explain that before taking on the research project, Peters and his colleagues made a deal with their backers that the study would be published regardless of the outcome.

That may well be on the up and up, but it doesn’t explain why the study was designed in such a way that the soda industry was probably confident that the odds were in its favor and that the results would be positive. Hill and his team only looked at people who already consumed diet drinks, and only for a relatively short period of time—during which they all were provided with professional weight-loss counseling.

Susie Swithers of Purdue University is one scientist not involved in the study who is ripping it to shreds. She tells NPR the research is “fatally flawed” and says it “leaves us with little science to build on.”

“This paper tells us nothing about the long-term health consequences that should be our real focus,” she says.

After reviewing dozens of studies published over the last five years that investigated the link between diet soda consumption and health, Swithers wrote an opinion piece last summer. “Accumulating evidence suggests that frequent consumers of these sugar substitutes may also be at increased risk of excessive weight gain, metabolic syndrome, type 2 diabetes, and cardiovascular disease,” she wrote. Among the studies Swithers cites was a 2008 study out of the University of Texas, which found that over the course of seven to eight years, those who regularly consumed artificially sweetened beverages were twice as likely to become overweight or obese as those who didn’t drink them. A study from the Bloomberg School of Public Health at Johns Hopkins University, published earlier this year, found overweight and obese adults who drank artificially sweetened beverages were likely to consume more calories overall per day than those who didn’t.

It’s been called the “counterintuitive effect” of drinking diet soda, and researchers are still not sure how to explain it. The most popular theory is that artificial sweeteners (found in diet soda, yes, but also other processed foods and beverages) muck up your body’s normal response to sugar intake, prompting you to seek out other sources of sugar.

In any case, the soda industry is probably thrilled to have a headline out there that tells diet soda drinkers what they want to hear. Decidedly “off message,” however, is the quote from one study participant, Kristi Norton, who was in the water-only group that cut out diet soft drinks altogether. “I felt like I could 1,000 percent tell the benefit of drinking water only,” she tells CNN. “I felt better. I had more energy. I felt healthier. I just generally felt way better, and I can feel the difference now when I drink a diet drink; I can feel this ‘heaviness.’ ”

Oh, and by the way, Norton lost 12 pounds during the study.