This is a really interesting hypothesis. It corresponds with several recent discoveries: - obesity: fecal microbiota transplants, when used to save patients fr

This is a really interesting hypothesis. It corresponds with several recent discoveries: - obesity: fecal microbiota transplants, when used to save patients from antibiotic-resistant clostridium difficile, resulted in unintended weight gain (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4438885/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4438885/) - allergies: using probiotics (or perhaps better, synbiotics) in conjunction with immunotherapy improves outcomes (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5209480/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5209480/, http://www.thelancet.com/pdfs/journals/lanchi/PIIS2352-4642(17)30041-X.pdf http://www.thelancet.com/pdfs/journals/lanchi/PIIS2352-4642(...) - emotions: brain-gut interactions affect emotional responses (http://journals.lww.com/psychosomaticmedicine/Abstract/publishahead/Brain_structure_and_response_to_emotional_stimuli.98803.aspx http://journals.lww.com/psychosomaticmedicine/Abstract/publi...) We aren't at the point where we can say "yes, this caused all of the changes in the 70s" but it seems to be a fruitful area of study.