Study related to diet soda and stroke risk is seriously flawed

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Study is drawing a growing body of criticism and skepticism from experts in the field of nutrition and science

The Calorie Control Council stated today that research findings presented during a poster session at the International Stroke Conference claiming an association between diet soft drink consumption and increased risk of stroke and heart attack are critically flawed.

"The findings are so speculative and preliminary at this point that they should be considered with extreme caution. In fact, the study has not been peer reviewed by any independent scientists and has not been published in a scientific journal," stated Beth Hubrich, a registered dietitian with the Council.

The research, as well as the publicity regarding the study abstract, is drawing a growing body of criticism and skepticism from experts in the field of nutrition and science.

"I have to say this is one of the worst studies I've seen capturing headlines in a long time," said Dr. Richard Besser, Chief Health and Medical Editor at ABC News, commenting during a February 10 segment on Good Morning America. "It's bad because of the science, but it's also bad because of the behavior that it can induce and the fear that people have. I don't think people should change behavior based on this study."

Pointing out some of the flaws in the study, Besser added, "They didn't look at how much salt they took in, they didn't look at what other foods they ate. Those things we know are associated with stroke and heart attack. They didn't even look at obesity over time. And so to conclude from this, that it's all from the diet soda, just makes no sense whatsoever."

Dr. Walter Willett, chair of the Department of Nutrition at Harvard School of Public Health, echoed this criticism in comments presented on ABCnews.com (http://abcnews.go.com/Health/video/taking-diet-soda-study-grain-salt-12870775): "It's important to keep in mind that his was really a preliminary report. It's not even published yet, and the study was fairly small. I think we have to interpret the findings about diet soda very carefully, in almost any first report, we shouldn't really change our behavior, because it could easily have occurred by chance."

The poster presentation is also at odds with statements on the website of the American Heart Association, sponsor of the conference where this poster was presented. Regarding the low-calorie sweeteners used in diet soft drinks, AHA states: "Try non-nutritive sweeteners such as aspartame, sucralose or saccharin in moderation. Non-nutritive sweeteners may be a way to satisfy your sweet tooth without adding more calories to your diet. The FDA has determined that non-nutritive sweeteners are safe."

Among the weaknesses and criticisms of the poster:

The poster is not a published study and has not been peer-reviewed for a scientific journal. As a result, it has not been examined by experts as to design, reasonableness of conclusions, and other methodological issues. The academic standards for poster presentations are lower than for peer-reviewed scientific journals, calling the conclusions into greater question.
The soda intake data used for this presentation are of questionable reliability. They are based on self-reported consumption figures, which are grouped into general categories, such as "moderate diet only" soda consumers. This imprecision makes it very difficult to draw any meaningful conclusions from the study.
This study is observational and does not show cause and effect. As a result, the presenters' conclusion that diet soda "may be associated with a greater risk of stroke, MI or vascular death than regular soda" is not well founded. For example, the authors do not appear to have controlled for such critical factors as family history of heart disease or stroke, or for weight gain. Also, stroke is more common in men 55 years of age and older and women 65 years or older. The average age of those in the study was 69.
The sample size of those who claimed they drank diet soda daily was small – only 4.5 percent of the total study sample.
The overall study population was not representative of the U.S. population, either in age (average age was 69), or race (only 20 percent non-Hispanic white).
Cardiovascular events are very complex statistically. Many people who have had a cardiovascular event (and therefore are a much higher risk for a second, statistically) are switched to a low calorie diet which will often include diet drinks as opposed to high calorie drinks.
The authors offer no explanation or theories for why diet soft drinks might be related to an increased risk of vascular events.
Low-calorie sweeteners are some of the most thoroughly studied food ingredients in the food supply. The safety of low-calorie sweeteners has been reaffirmed time and again by leading health and regulatory groups worldwide.