Friday, August 30, 2013

Overselling the microbiome award: Swiss National Science Foundation on smoking, weight gain and bacteria

Well, I guess I should thank Mark Martin for pointing me to this story: Weight gain in ex-smokers likely caused by changes in intestinal bacteria, not increased appetite | National Post.  It - and the Press Release it seems to be based on Why smokers gain weight when they quit smoking are a horrendous example of "Overselling the microbiome". (The paper connected to the press release is in PLOS One and seems to not have oversold the findings in the same way).  I am so sick of these types of stories and PRs I am not going to go into this in much detail but here are some comments

National Post:
  • The title alone shows how badly they were misled by the authors: there is NO evidence that changes in bacteria caused anything here.
  • "Have you noticed that you gain weight every time you quit smoking?" ... "you may be surprised to learn that it has little to do with your calorie intake."  "Researchers attributed the weight gains to changes in the bacterial diversity of the intestine."
  • Thanks "researchers" for misleading everyone about your study.

  • "Most smokers put on a couple of kilos when they quit smoking. This is not due to an increased calorie intake, but to a change in the composition of the intestinal flora after quitting smoking"
  • "attribute the cause to a changed composition of the bacterial diversity in the intestine."
I can't even go on.  The issue is simple.  The researchers did not show that the bacteria caused ANYTHING.  They just showed that the bacteria found in people after quitting smoking were different than before quitting.  And they also showed that these people had some other changes in their systems after quitting - like weight gain.  Does this mean the bacteria caused anything.  NOOOOOO. I am just going to give the Swiss National Science Foundation my coveted "Overselling the microbiome award" for a misleading and inaccurate and potentially dangerous press release.


  1. I kind of feel badly I even mentioned it. I don't want to be the Bearer of Dumb Press Releases. But thank you for fisking this.

  2. Hello, I couldn't find an email address so I have posted this here - sorry.

    I am the webmaster of , a website aiming to be a definitive source of broad based information about the Tree of Life, bringing together much of the 'splintered' information on the internet into one catalogue - this will soon be supported by a blog to allow for public comment and contributions from individuals to expand the information source. The site is not designed to be technical but more generally informational and as you will see is still in the early development stage.

    I would like to add some references to your blog on my site and hope that you are OK with this.

    I would also like to request that you link from from your blog to my site, which I will reciprocate, such that we have reciprocal linking to each others mutual benefit.

    I look forward to your positive reply.

    kind regards,
    Mike O'Shannessy

    p.s. I also own the domain which is yet to be launched


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