Dietary Fibre in Pea Cotyledon Used as a Protein Source Provides Multidimensional Protection Against Colonic Protein Putrefaction

Background/Objectives: Substitution of plant-based for animal-based protein sources has been recommended to reduce global non-communicable disease burdens, including colorectal cancer. Objective: The goal of this study was to determine possible ways that pea cotyledon may modulate hindgut concentrations of protein putrefaction products implicated in colorectal cancer by comparing diets based on casein, meat or pea cotyledon in a rat model. Method: Rats (n = 8 per treatment) were fed for 9 days on 18.6% protein diets containing casein, meat, or yellow split peas as sole protein sources. Faecal samples were collected daily from day 6 onwards and gut samples post-mortem for analysis. Protection by hindgut contents against protein putrefaction products was assessed using a novel secondary in vitro fermentation of the rat faeces with human faecal inoculum and added protein. Results: Compared with the average of non-pea diets, which was similar to one another, pea cotyledon increased caecal digesta content (101%, p < 0.001), faecal dry matter (116%, p < 0.001), faecal water-holding capacity (66%, p < 0.001) and hydrated faecal mass (235%, p < 0.001). Caecal putrefaction product concentrations (p-cresol, indole, and phenol) were 72% lower on the pea diet compared with the non-pea diet average (p < 0.001). The pea diet altered the microbiota composition and downregulated tryptophanase activity while increasing butyrate production by 236% (p < 0.001). During ex vivo fermentation with added protein pea-fed rat faeces suppressed protein putrefaction and promoted butyrate production, whereas faeces from other diets were as ineffective as the no-faeces control, showing that distal transfer of more than enough pea polysaccharides to sustain distal colonic saccharolytic fermentation had occurred. Conclusions: Dietary fibre associated with protein in pea cotyledon protects against protein putrefaction products by bulk dilution, a decreased residence time, changing microbiome composition and function, and distal displacement of fermentable dietary fibre, therefore providing multidimensional protection.