COMBINING WHEAT BRAN WITH RESISTANT STARCH RAISED FAECAL BUTYRATE and LOWERED FAECAL PHENOLS IN HUMAN VOLUNTEERS CONSUMING A DIET HIGH IN RED MEAT

Abstract

Fermentation of undigested carbohydrates [non‐starch polysaccharides (NSP) and resistant starch (RS)] and protein in the colon may contribute to the aetiology of colorectal cancer (CRC). Byproducts of carbohydrate fermentation include the short chain fatty acids (SCFA) acetate (Ace), propionate (Prop) and butyrate (Buty). Butyrate inhibits proliferation of CRC cells in vitro and may induce differentiation and apoptosis. Products of protein fermentation include tumorigenic ammonia and phenols (p‐cresol and phenol). The aim of this study was to investigate the effect of combining unprocessed wheat bran (WB) with RS on fermentation‐dependent events in the distal colon of on a diet high in lean red meat. The study was a randomised crossover block design of a total of 11 weeks (including 3 × 3 weeks of dietary study and 2 × 1 week breaks between dietary periods). Twenty volunteers (10 female) with a family history of CRC were randomized to either Diet 1 (control diet = 250 g red meat/day + low RS + low WB); Diet 2 [WB diet = 250 g red meat/day + low RS + unprocessed WB (10 g dietary fibre/day)] or Diet 3 [WB/RS diet = 250 g red meat/day + RS (25 gRS/day) + WB (10 g dietary fibre/day)]. Lean red meat, RS (coarsely ground Himaize™) and WB were supplied. All food and drink consumed during the study was recorded. During the final week of each 3 week dietary period subjects collected total faecal output for 5 days (days 15–19) for analysis of faecal variables (see Table). Rectal biopsies were taken on the morning of day 20 (analysis in progress). Diet Faecal output (g/day) Faecal SCFA(mmol/L) Faecal SCFA (mmol/day) Phenols (μg/g faeces) Ace Prop Buty Ace Prop Buty Phenol p‐cresol 1 131 ± 14 59 ± 4 16 ± 1 15 ± 1 8 ± 1 2 ± 0.3 2 ± 0.3 3.1 ± 5 102 ± 71 2 161 ± 15 59 ± 4 14 ± 1 16 ± 1 10 ± 1 2.5 ± 0.3 3 ± 0.4 3.4 ± 5 81 ± 46 3 204 ± 19 68 ± 5 14 ± 1 26 ± 3 14.6 ± 2 2.8 ± 0.3 6 ± 1 1.8 ± 4 61 ± 42 Mean ± SD; Faecal variables in italics are significantly different (P < 0.05) in test diet vs. Control diets. The combination of unprocessed wheat bran and RS had a greater impact on fermentation‐dependent events (i.e. increased faecal output, increased butyrate concentration and lowered faecal phenols) than WB alone (Table). The combination of WB and RS may have important implications for the dietary modulation of CRC risk especially in the distal colon. The results also highlight the benefits of increasing dietary intake of indigestible carbohydrate relative to protein sources such as meat.