Friday, April 20, 2012

Could Dr. Oz be Wrong?

I saw a Dr. Oz video today on yahoo about diet foods that make you gain weight.  I was disappointed to find diet sodas in his commentary. Why? Because the study he quotes on the video does not show that diet sodas cause people to gain weight at all. This one study has been so badly misinterpreted that just about everyone thinks that it is a fact that diet sodas will make you gain weight.
Here’s the problem: the study that is constantly quoted as “proving” that diet sodas cause weight gain can’t show cause and effect at all. It is an observational study. The researchers used people’s self-reported intake of diet sodas over a nine-year period and then looked at what happened to their weight during that same time. Just because the people who drank more diet soda were also the people who gained more weight does not mean that one caused the other. This doesn’t make it a bad study. The problem is that media headlines and reports – including Dr. Oz’s video – do not accurately report what this study showed – or did not show.

If you read the actual study, at the end, the researchers themselves say that there may be no causal relationship at all between diet sodas and weight gain. They also discuss other studies – intervention studies that can show cause and effect – that mostly show that artificial sweeteners don’t cause an increase in hunger and weight gain.  Add that to what we know about the inaccuracies in self-reported food intake and you can see that this study, while interesting, does not show that diet sodas cause weight gain.

So why does the media continually misreport these studies? My suspicion is that, perhaps, they like hyped up, simplified headlines. They may not take the time to read the actual study on which they’re reporting relying, instead, on the study press release. They also don’t seem to be reporting about what the body of scientific literature is showing on a particular topic – rather, showcasing one study that is unlikely the definitive work on the subject.

In the interest of self-disclosure, I must tell you that I don’t regularly drink diet sodas myself – maybe two or three week. Nor do I think that they are good for you. But I also don’t think they are particularly bad for you. Future intervention studies could possibly show that they somehow impede weight loss – but as of now, the studies don’t show this.

Bottom line? The jury is still out on this one. If there is an effect, it will likely be different for different people. To state that diet sodas cause hunger and weight gain as though it is a fact is a misinterpretation of the scientific data available at this time.

If you’re interested in learning more about media reporting on scientific studies, check out this website:

Beth Kitchin, PhD, RD
Assistant Professor, Nutrition Sciences
University of Alabama at Birmingham