Habitual consumption of high-fibre bread fortified with bean hulls increased plasma indole-3-propionic concentration and decreased putrescine and deoxycholic acid faecal concentrations in healthy volunteers

Only 6 to 8% of the UK adult population meet the daily recommendation for dietary fibre. Fava bean production and processing leads to vast amounts of high fibre by-products such as hulls. Bean hull fortified bread was formulated to increase and diversify dietary fibre while reducing waste. This study assessed the bean hull: i) suitability as source of dietary fibre; ii) the systemic and microbial metabolism of its components and iii) postprandial events following bean hull bread rolls. Nine healthy participants (53.9 ± 16.7 years) were recruited for a randomised controlled crossover study to attend two intervention sessions, each lasting three days, involving the consumption of two bread rolls per day (control or bean hull rolls). Blood and faecal samples were collected before and after each intervention sessions and analysed for systemic and microbial metabolites of bread roll components using targeted LC-MS/MS and GC analysis. Satiety, gut hormones, glucose, insulin, and gastric emptying biomarkers were also measured. Two bean hull rolls provided over 85% of the daily recommendation for dietary fibre; but despite of being a rich source of plant metabolites (p=0.04 vs control bread), these metabolites had a poor systemic availability. Consumption of bean hull rolls for three days significantly increased plasma concentration of indole-3-propionic acid (p=0.009) decreased faecal concentration of putrescine (p=0.035) and deoxycholic acid (p=0.046). However, had no effect on postprandial plasma gut hormones, on the bacterial composition, and on the faecal short chain fatty acids amount. Therefore, bean hulls require further processing to improve their bioactives systemic availability and fibre fermentation.