Differing effects of pectin, cellulose and lignin on stool pH, transit time and weight.

Randomized cross-over studies were undertaken to determine the effects of daily dietary supplements of pectin (12 g/d), cellulose (15 g/d) and lignin (12 g/d) on stool characteristics of healthy volunteers. Detailed dietary records were kept throughout the study. Stool collections over 48 h were used to determine mean stool pH and weight. The single stool transit time was measured using radio-opaque markers. Pectin did not significantly alter the mean stool pH, transit time or 24 h wet weight. Cellulose lowered the mean stool pH from 6.38 to 6.12, decreased mean stool transit time by 27% and increased mean wet stool weight by 57%. Lignin lowered the mean pH from 6.34 to 6.25, decreased the stool transit time by 20% and increased stool weight by 27% but these changes were not statistically significant. These findings have shown that individual fibre components have different colonic metabolic effects and support the view that associations between dietary fibre intakes and diseases such as colorectal cancer should be evaluated with regard to the type of fibre components consumed.