This study, which appeared in Gut, explored how diet and exercise correlate with differences in the gut microbiota.


The researchers collected faecal and blood samples from professional rugby athletes (male elite professional players) that were compared with control subjects (healthy males). Also, compositional analysis of the microbiota of both groups was explored by performing 16S rRNA analyses. The results indicated that the athletes differed on measures of protein intake and plasma creatine kinase (which marks extreme exercise); and, more interestingly, they presented a higher diversity of microorganisms in their guts.


The study gave evidence that exercise may impact gut microbiota diversity, but in human subjects extreme exercise often co-occurs with extreme diets, making causality difficult to pin down.


Consequently, this paper generated a lot of reaction. Jonathan Eisen, Professor at UC Davis, commented on this paper and its media coverage through his blog, The Tree of Life, in an article titled “Please make it stop – overselling the microbiome award for rugby, exercise, microbiome stories”. At issue was whether the authors (and journalists covering the paper) were clear enough about correlation versus causation. Lively Twitter conversations ensued. The controversy served as a reminder to use careful language in article abstracts and news items alike, in order to best represent the science.



Clarke S et al. (2014) Exercise and associated dietary extremes impact on gut microbial diversity Gut 63(12), pp. 1913-1920. doi:10.1136/gutjnl-2013-306541