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 


  1. Dr. Kitchin,
    I agree with your opinion on why the media constantly misreports these types of results. In my opinion, it takes an assessment of several study results, since there are many variables that may occur in any one study. Collaboration of results from those studies would give one a more accurate picture. It is wrong to report results from one single study, especially an observational study.
    Stephanie Biggers

  2. Dr Kitchin,
    I agree with what you are saying. My doctor show us the best demonstration. He put a balloon over a 20 oz soda bottle and shook it slightly. The balloon began to expand. He told us that the balloon is like our stomach. When we drink sodas even diet sodas they expand our stomachs allowing us to hold more food. Also he told us to be careful because alot of them are high in sodium.

  3. Thank you for your comment Nicole. But your doctor is wrong about sodas being high in sodium. A can of diet coke has 56 mg of sodium - that is a mere 2% of your daily limit for sodium - a fairly insignificant amount! Also, I don't recommend using a balloon to mimic the effects of soda on the stomach! Our stomachs are very different from balloons! There is no evidence that foods that increase gas in the intestine increase the amount of foods we eat. In fact, some foods, like fiber, that produce gas in the intestine, actually reduce how much food we eat. So,I really question the scientific validity of the balloon method for studying the effects of diet sodas on how much we eat! Remember, not many doctors are trained in nutrition - so they are not always a good source of nutrition information!

  4. Thank you! I hope to find the basic knowledge I need to know about nutrition by the end of our course. Maybe more weight loss clinics' patient's would be more successful with his/her weight loss if they had a nutritionist on board.
    I stopped drinking diet drinks for a long while because I thought it was making gain weight.

  5. Hi Dr. Kitchin
    Yes he could very well be wrong about diet soda causing hunger and weight gain. What we do know is that everybody has a different metabolism rate at which they burn and/or store calories. As you have already mentioned, there is no proven cause and effect.

  6. Hi Dr Kitchin
    Yes Dr Oz could be wrong about diet soda causing weight gain and hunger. What we ARE sure of is that everbody has a different metabolism rate at which they store and/or burn calories. As you have already mentioned, there is no proven cause and effect. Also, we know that social bias and memory bias could be a factor in the accuracy of the study.