Abstract

The effect of dietary manipulation on faecal enzyme activities was studied in six healthy volunteers who consumed a mixed, free choice diet (control) or that diet with additional apple pectin (18 g/day), wheat bran (30 g/day) or fat (total greater than 150 g/day) for periods of up to 3 weeks. Control and test diets were alternated over a continuous period of 5 months. Food consumption was recorded and showed that in control periods each subject maintained a high fat (approximately 40 per cent of daily calories) and moderate plant fibre (approximately 18 g/day) intake. Pectin and bran decreased faecal bacterial β-glucosidase and β-glucuronidase activities, and pectin increased the stool concentration and rate of formation of ammonia by faecal incubations in vitro, but fat supplementation was without consistent effect. The results demonstrate that plant cell-wall components, but not dietary fat, significantly influenced the enzymic activity of the faecal microflora from subjects maintaining a mixed dietary intake typical of the UK.