Thursday, June 30, 2016

A Letter to the Editor Criticising the Paleo Mouse Study

A paper was published in February 2016 claiming that they tested the effect of a Paleo diet in mice and found that it causes excess weight gain, impaired glucose tolerance and insulin resistance [1].  I dubbed the paper ‘the Paleo mouse study’ and have written about it earlier in the year.  I discussed that mice respond differently to higher fat diets than humans*.  And also, that the LCHF diet is the Paleo mouse study sucks as it was largely comprised of added fats, casein and sucrose whereas the standard low fat diet was a lot more whole foods based

A letter to the letter by Nathan Cofnas** was recently published that brought up some issues with the Paleo mouse study [2] (it’s short, open access and I recommend reading it):

  • The representation of the study in the media*** and on Melbourne University’s Youtube channel was that this study was a test of a LCHF Paleo diet (never mind the details on what the mice actually ate), but the paper didn’t even include the word ‘Paleo’ or ‘Paleolithic’
  • The Paleo concept is based on evolution and genetic adaptation and would make the hypothesis that animals do best on the diets that they are most genetically adapted to, which can be largely inferred from what they eat in the wild.  For mice, this is a low fat, high carbohydrate, largely plant based diet, so it would be expected that the chow diet would be better for them 

But one thing the letter didn’t mention much of are results from human RCTs, which trump and contradict and mouse studies.  Meta-analyses of low carb vs. low fat RCTs [3] or Paleo vs. conventional dietary advice RCTs [4] both find that low carb and Paleo diets result in greater weight loss than the alternative, and more recent studies continue to support these findings [5, 6]

* For example, the senior author of the Paleo mouse study recommends the Mediterranean diet, but the amount (~40% of total calories) and type (olive oil/MUFA) of fat promoted in the Mediterranean diet causes obesity, glucose intolerance and insulin resistance in mice [7, 8]

** He is part of the Department of History and Philosophy of Science at the University of Cambridge and has published some earlier work on evolutionary mismatch [9].  Leave it academics outside the field and bloggers to apply some common sense in translating studies to the real world 

*** For example: “To put that in perspective, a 100 kilogram person on a Paleo diet could pile on 15 kilograms in two months” [10] (good luck achieving half that effect with a deliberate overfeeding study in humans)

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