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Chocolate, weight loss, bad studies and bad journalism

Dark ChocolateOn Friday a documentary aired on German and French television channel Arte about dietary and weight loss studies. The authors of the documentary had done an experiment where they created a fake study claiming that eating dark chocolate can help with weight loss. The study was done in cooperation with science journalist John Bohannon, who wrote about the experiment on

They did a real study and published it in a journal, but it was obviously flawed in many ways. They published a press release and created a webpage for an Institute of Diet and Health which doesn't exist. Shortly afterwards a number of media outlets started reporting about this study, the first big one was "Bild", the largest German newspaper.

There are a number of ways in which this study was flawed:
  • The study had 15 participants, which is a very low number for such a study.
  • The study was published in an obviously bad journal (International Archives of Medicine). There is a large number of such scientific journals that publish just anything if you pay them for it. Recently there was a case where someone successfully submitted a paper only containing the sentence "Get me off Your Fucking Mailing List" to such a journal.
  • In the documentary it is mentioned that during the measurements the participants in the control group received a glass of water before they where weighted.
  • The authors where cherry picking their results. They did a lot of measurements on the study participants. By pure chance one of the value they measured would improve in a significant way. This kind of flaw in scientific studies is best explained by this xkcd comic.

The last point is probably the most interesting, because it can not necessarily be spotted in the final publication. One way to avoid this is the pre-registraiton of studies in public trials registers together with the methodology. There is increasing pressure to pre-register trials in medicine. Unfortunately, that debate has rarely received the field of nutrition, study registration is rarely done at all in that field.

The point of all this is of course that studies on nutrition aren't much better. While the whole story got a fair amount of praise, there was also a debate about the ethics of such a study. The questions at hand here aren't so simple. Obviously the participants of the studies were misled. However it is not uncommon to mislead participants of studies about the real intent of the research. In psychology a lot of studies would be just impossible to conduct otherwise.

Another point of criticism is that the study wasn't approved by an institutional review board. It'd be an interesting question if an ethics board would've approved a study with the pure intent to show flaws in journalism and the scientific publication process.

My personal opinion is that the ethical issues raised by such a stunt are at best minor compared to the ethical issues with all the supposedly serious studies that get published all the time and have the same flaws.

The only issue I might have with the whole story is that I feel the reality is often even grimmer. I'm pretty sure that with more effort the study could've been published in a real journal. The fallback to an obvious fraud journal was according to Bohannon due to the time constraints of the documentary.

Often enough media stories about health and nutrition (and also about a lot of other things) aren't based on studies at all. It's not rare that these stories are merely based on opinions by single researchers, preliminary lab research or yet unpublished studies.

I don't know if this was the source for the chocolate study idea, but three years ago the British Medical Journal had a publication about the positive effects of the ingredients of dark chocolate. Not only did that trigger a number of media reports, the German Society of Internal Medicine (DGIM) issued a press release seriously proposing that health insurances could cover the costs for dark chocolate for patients with metabolic syndrome. (Here's a talk by Gerd Antes mentioning this issue.)

These things happen on a daily basis, and they don't just happen in nutrition science.

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