Gut instinct

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3596024/

http://www.bmj.com/content/345/bmj.e6144

http://www.ingentaconnect.com/content/rcgp/bjgp/2002/00000052/00000478/art00011?token=005c1dddc36b2f703bb1b67232d45232b5f7a736a2d3b7441287a783568293c62207d673f582f6b16d5dd1d78d40

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3207087/

http://www.bmj.com/content/347/bmj.f6857