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The effect on colonic function of adding wheat fiber for 3 weeks to the metabolically-controlled diets of six healthy volunteers has been studied. Increasing dietary fiber intake from 17 to 45 g/day increased fecal weight from 79 +/- 6.6 g/day to 228 +/- 29.9 g/day and shortened mean transit time, measured by a continuous marker method, from 57.8 +/- 8.3 hr to 40.3 +/- 8.9 hr. The increase in fecal weight was largely due to water. Fiber caused a dilution of fecal marker and an increase in fecal fat, nitrogen, and calcium output. Fecal sodium, potassium, and chloride showed only small changes but volatile fatty acid output increased significantly without concentrations changing. Fecal bile acid output increased from 199 +/- 46 mg/day to 279 +/- 46 mg/day. These changes are discussed in light of current views of the role of dietary fiber in protecting against colon cancer.

An investigation was made of the effect of changing mean transit time (MTT) by administration of drugs which affect colonic motility on faecal microbial mass in man. Senokot was used to accelerate and codeine and/or loperamide to prolong transit in subjects maintained on a constant high fibre diet. Doses of Senokot or codeine/loperamide were adjusted to halve or double transit time measured during a three week control period on diet alone. Stools were collected throughout and analysed for bacterial mass by a gravimetric procedure. Transit was measured by a continuous marker method. Senokot decreased mean transit time from 63.9 to 25.0 hours (n = 6), with increased stool weight from 148 to 285 g/day. Bacterial mass increased in all subjects from a mean of 16.5 to 20.3 g/day (dry weight) (p less than 0.025). Codeine/loperamide increased mean transit time from 47.1 to 87.6 hours (n = 5), with decreased stool weight from 182 to 119 g/day. Bacterial mass decreased in all but one subject from a mean of 18.9 to 16.1 g/day (NS). There was a significant correlation between transit time and bacterial mass in all three periods (r = 0.77, p less than 0.001). Changes in transit time are shown to alter microbial growth in the human colon and result in altered stool output, on a constant diet. Factors which affect transit may be as important as diet in determining large bowel function and hence susceptibility to disease.

We measured fecal composition after giving oral doses of mannitol, lactulose, or raffinose to ileostomy patients and to normal subjects in order to determine the colon's capacity for metabolizing these carbohydrates and to decide whether volatile fatty acids (VFA) or unabsorbed carbohydrate initiated diarrhea. Seventy-four percent of mannitol, 100% of lactulose, and 88% of raffinose passed unabsorbed through the small intestine of six patients with ileostomies. Dose-response experiments revealed that normal subjects could tolerate 120-220 mmol of mannitol, 73-146 mmol of lactulose, or 80 mmol of raffinose before fecal output of water exceeded 400 ml in 48 h or before test carbohydrate appeared in the stool. Mannitol could be metabolized to glucose; lactulose to fructose, galactose, and glucose; and raffinose to sucrose, melibiose, fructose, galactose, and glucose. The output of VFA in fecal water did not correlate with the moles of carbohydrate metabolized, and it did not greatly exceed the output of VFA in stools of equal volume that were induced by nonfermentable MgSO4. We conclude that the human colon is capable of removing appreciable amounts of single doses of these carbohydrates from fecal water. When this capacity is exceeded, unabsorbed carbohydrate rather than VFA prompts an increased output of fecal water.