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.

  7. Dr. Kitchin,
    Is it possible that diet sodas cause you to feel less full than sugary sodas, and folks consequently drink more of them? Or folks think that because they are diet, they will NOT experience weight gain if they drink more of them? For example, if a normal soda has 200 calories (I'm probably way off, but just for the sake of the example), and a diet soda has 150 calories, but I do not know the actual caloric difference, I may think that I can get away with drinking two diet sodas, thinking that they are the equivalent of one when in fact they add up to quite a bit more (300 calories).
    Kimberly Wendland

  8. Dr. Kitchin,
    I am unsure about this study. I think like previously stated by another classmate, there needs to be more studies and research should not be based off one particular study itself. My particular experience is what has me unsure of the study. I used to drink about three sodas/diet sodas or more a day. After I cut out the sodas and sweet tea I saw a good change in my weight. So was it the sodas causing me to maintain that higher weight? I'm not sure. With my experience I can see how this study would make sense. People also have to consider that these people being observed probably had other things besides diet soda in the whole nine years, like alcohol which can contribute to weight gain.
    Abby Hall

  9. Many many years ago, some researcher did an "observational study" on what makes the sun rise and set and concluded that the Sun must circle the Earth, and people believed that for many years until someone decided to actually do some real science. Observation is necessary in research, but it is not sufficient. Not to beat up too much on "physicians" but most know very little about research, which is the irony because they constantly use physicians to make these claims based on research that the physicians really don't understand themselves. They don't understand research design, inferential statistics, internal and external validity, ecological validity, etc. They learn a little bit about it in medical school, but they aren't required to actual do it. I see Dr. Oz sitting on the beach, and looking up at the sky with a geocentric view of the universe. :) Darryl L. Townes, PhD, PDMS

  10. Dr. Kitchen,
    This is all very interesting to me. I'll admit I am one of the many that have fallen for the "diet sodas make you fat" gimmick. Thank you for exposing the truth about this research and the media. I will definitely look into nutritional studies that the media presents in a different light and do my research! I myself am not one who drinks sodas at all really simply because I worry about tooth enamel damage. Also, like you said, while they aren't necessarily bad for you, they don't pack nutrients in them. I try to focus on getting my daily water intake. After I've reached that, I usually don't want anything else to drink! Point being, I agree with your above statements totally. Thank you for enlightening me!

  11. Hi Dr. Kitchin,
    I find the correlation between drinking diet sodas and weight gain pretty interesting. Could it be that by drinking a soda that is less bad for you the participants figured that they could allow themselves more wiggle room on the types of foods they were consuming? e.g. "I've been good with my diet today by drinking that diet soda, now I can have that slice of cake."

  12. Dr. Kitchin,
    I like the idea of diet drinks but I can't stand the taste of them, especially diet coke. The only soft drink I like is when it has sugar in it. I was wondering, I saw from your lectures, but does sugar really have a cocaine-like stimulation to it, or is it all placebo? I'm sure for kids it is but my psychology professor said something about how cocaine stimulates in a similar way to sugar. What are your thoughts on this?


    1. Thank you so much for your comment and question.

      I'm like you - I only drink a few diet cokes a week at most because I find that when I drink too many, I start disliking the taste. I usually drink one or two when I am working in osteoporosis clinic because they are part of our lunch and I don't like plain water. I usually drink mineral water with some juice added or unsweet iced green tea with my lunch. While sugar may stimulate the same brain areas that cocaine does, that does not mean it is addictive like cocaine is. There are many things that stimulate the same areas of the brain as cocaine - such as intense passion and love! To be classified as addictive, a substance must cause physical dependence. Dependence is a combination of two symptoms: tolerance and withdrawal. We really don't see that with sugar. While food on the whole can have addictive qualities, some of that is cognitive/behavioral addiction. But this idea that sugar is like cocaine is silly. That said, we should definitely enjoy sugar in small amounts! Here is a really good article on this topic:

    2. I want to clarify that I am not saying that your psychology professor was saying that sugar is just like cocaine and that he/she was silly! I was referring to headlines that I see telling you that "sugar is just like cocaine!". thanks!