[1] Univ Bristol, Sch Oral & Dent Sci, Bristol BS8 1TH, Avon, England
[2] Univ Bristol, Sch Social & Community Med, Bristol BS8 1TH, Avon, England
[3] Univ Hosp Bristol Educ Ctr, Natl Inst Hlth Res, Biomed Res Unit Nutr Diet & Lifestyle, Level 3,Upper Maudlin St, Bristol BS2 8AE, Avon, England
[4] Univ Hosp Bristol NHS Fdn Trust, Dept Coloproctol, Bristol, Avon, England
[5] Derriford Hosp, Dept Gastroenterol, Plymouth, Devon, England