OBJECTIVE: To investigate the mechanisms of constipation and the effect of fiber supplementation on physiology, mechanisms, stool parameters, and colonic transit times in a group of constipated older patients. DESIGN: Single-blind, randomized, placebo-controlled fiber intervention with crossover. SETTING: A university-based outpatient center. PATIENTS: Ten community-living older men and women, healthy except for chronic constipation. INTERVENTIONS: Patients were given either 24 g psyllium fiber or placebo fiber daily for 1 month, then crossed over to the other arm for an additional month. Structured testing, including total gut transit time and rectal and colonic manometry, was performed at the end of each intervention month. Patients recorded stool frequency, consistency, and weights daily. RESULTS: The predominant mechanism for constipation in these patients was outlet delay caused by pelvic dyssynergia. Fiber decreased total gut transit time from 53.9 hours (placebo condition) to 30.0 hours (P < .05). Stool weights and consistency were not significantly improved by fiber, though there was a trend toward an increase in stool frequency (1.3 vs 0.8 bowel movements per day.) Pelvic floor dyssynergia was not remedied by fiber, even when constipation was clinically improved. CONCLUSIONS: Fiber supplementation appeared to benefit constipated older patients clinically, and it improved colonic transit time, but it did not rectify the most frequent underlying abnormality, pelvic floor dyssynergia.
