A new study that focused on diet soda and mortality may not be as grim as it seems. Several news outlets decried diet sodas as lethal when the research was published last week. Here’s why it may be too early to panic.
The new soda study, which was published by the peer-reviewed Journal of the American Medical Association (JAMA), focused on proving or disproving a link between drinking more than two cups of any kind of soda per day and higher risks of early death. On the one hand, researchers noted a correlation between high soda consumption and mortality, which caused a swift and notable backlash in the media and the public. However, correlation between two events is not the same as causation. In other words, many other lifestyle factors could play into the early deaths reported by the researchers. The data needs more unpacking and less sensationalizing before we react.
Caveats, Confounding, and the Bigger Picture
The results of the study sound particularly concerning. “In this population-based cohort study of 451,743 individuals from 10 countries in Europe, greater consumption of total, sugar-sweetened, and artificially sweetened soft drinks was associated with a higher risk of all-cause mortality,” the published material said. “Consumption of artificially sweetened soft drinks was positively associated with deaths from circulatory diseases, and sugar-sweetened soft drinks were associated with deaths from digestive diseases.”
However, near the bottom of the published study, the researchers make an important caveat that seems to have gone largely unnoticed. “Given the observational design of the study, it is not possible to establish causality between soft drink consumption and mortality, and we recognize that the observed associations may be biased because of residual confounding.”
What does that mean? According to a Boston University School of Public Health website, residual confounding is “the distortion that remains after controlling for confounding in the design and/or analysis of a study.” In other words, unaccounted-for factors could unintentionally skew the results of a study. In an exclusive interview, a Florida State University professor told us why the sudden panic over diet sodas may need some mitigating.
“If we think logically about this, should you be drinking a soda? Probably not,” said Dr. Michael Ormsbee, Associate Professor in the Department of Food, Nutrition, and Exercise Sciences and Assistant Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. “Diet soda? Probably not. But if you’re managing calories, switching to a diet soda may be better. Do you eat out more or less? Do you exercise? If so, how much? All these things complicate research studies so much that it’s hard to get data on a specific topic.”
In Defense of Diet
Dr. Ormsbee urged caution on taking the media frenzy regarding the JAMA study too seriously, citing reduced calories as one potential benefit of switching to diet as opposed to staying with full-sugar soft drinks. “A lot of people turn to diet sodas as a way to manage calorie intake,” he said. “Larger studies—meta analyses—kind of group all the data together on diet soda and non-nutritive sweeteners. They come back saying that when they pool all the data, there’s lower caloric intake by having these types of drinks.”
“We know [sodas] are chemicals in a can—so how good can that be?—but if you’re going to drink them, which is the lesser of two evils?” Dr. Ormsbee said. “You can have a diet soda here or there and you’re going to be fine, but incorporate healthy activities like exercise.”
Finally, we spoke about recent soda taxes that have passed, which intend to curb potential health complications associated with soft drink consumption.
“In the case of these diet drinks, there are clearly cities that have imposed soda taxes and they’re starting to see different health outcomes,” Dr. Ormsbee said. At the same time, some people may react to soda taxes by simply drinking oversized sodas instead of multiple smaller ones.
“I think if you compare it to what happened with cigarettes, just making it more and more expensive and more difficult to smoke inside, that’s dropped the rate of smoking nationwide,” Dr. Ormsbee said. “In theory, it could be a benefit, but volume is going to still be an issue.”
For now, although no soda is truly healthy, diet sodas still have the benefit of reduced caloric intake. And while the results of the JAMA study may shock us, correlation does not equate to causation—as the researchers themselves noted.
Dr. Michael Ormsbee contributed to this article. Dr. Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. He received his Ph.D. in Bioenergetics from East Carolina University.