Polydextrose is a new soluble food ingredient which cannot be digested by intestinal enzymes and so may affect colonic function. Studies in healthy volunteers compared the effects of diet supplementation with 30 g/day polydextrose, a standard dose of 7 g/day ispaghula and two mixtures containing 2 g/day ispaghula with either 30 g/day polydextrose or 10 g/day polydextrose with a control period. During the 10-day periods, the mass, frequency and consistency of faeces were assessed as well as the whole-gut transit time, ease of defaecation, flatulence and palatability of the preparations.

All preparations significantly increased the weekly faecal mass above control values (P < 0.05) but there were no significant differences between the preparations. Transit time and stool frequency were not affected significantly by any of the preparations (P > 0.05). Both preparations supplying 30 g/day polydextrose softened stool consistency equally but the other preparations had no effect. All preparations caused flatulence and other gas-related problems but polydextrose caused more than ispaghula, even at the lowest dose of 10 g/day. More volunteers preferred taking the polydextrose drinks than the sachets of ispaghula which formed a viscous drink with water.

Despite superior palatability and equally effective stool bulking, polydextrose is unlikely to be an alternative laxative to ispaghula because of the unacceptable levels of flatulence.