Footnotes

• Contributors MD had the original idea, and designed the study together with AF; SW, AA, LE and LA collected material, characterised the study subjects and acquired data; F-AH, AF and JFB performed microbiota sequencing; data analysis and interpretation were done by FH, MB, FB, JR and MD. FH, MD and JR drafted the manuscript with critical revision from all authors.

• Funding Supported by funds from the Swedish Research Council (Vetenskapsradet) to MD; European Union Seventh Framework Programme (FP7/2007-2013, grant number 262055, ESGI) to MD and AF; Iranian ministry of health and medical education to FH.

• Competing interests None declared.

• Ethics approval Karolinska Institutet, Stockholm, Sweden.

• Provenance and peer review Not commissioned; internally peer reviewed.