Macronutrient absorption characteristics in humans with short bowel syndrome and jejunocolonic anastomosis: Starch is the most important carbohydrate substrate, although pectin supplementation may modestly enhance short chain fatty acid production and fluid absorption

Background: Diet may play an important role in the management of patients with short bowel syndrome who have colon in continuity. However, macronutrient absorption has not been well characterized, and the most appropriate dietary constituents have not been well defined. Objective: To define carbohydrate absorption characteristics in patients with short bowel syndrome and determine the potential role of pectin as a dietary substrate. Methods: The authors studied the effect of a custom pectin-based supplement in 6 subjects (3 male/3 female) aged 29-67 years with jejunocolonic anastomosis, 4 of whom required long-term parental nutrition. Small intestinal absorption capacity, macronutrient and fluid balance, gastrointestinal transit time, and energy consumption were measured. Results: Data showed that 53% nitrogen, 50% fat, and 32% total energy were malabsorbed. In contrast, the majority (92%) of total carbohydrate was utilized. Fecal short-chain fatty acids (SCFAs) were increased, an indication of increased fermentation. Although only 4% of starch was recovered in stool, it is indicative of considerable starch malabsorption, thus providing the main carbohydrate substrate, for colonic bacterial fermentation. In contrast, non-starch polysaccharide was a relatively minor fermentation substrate with only 49% utilized. Eighty percent of the pectin was fermented. Supplementation was associated with increased total SCFAs, acetate, and propionate excretion. There was a trend observed toward greater fluid absorption (-5.9% ± 25.2%) following pectin supplementation. Nonsignificant increases in gastric emptying time and orocolonic transit time were observed. Conclusion : Despite malabsorption, starch is the primary carbohydrate substrate for colonic bacterial fermentation in patients with short bowel syndrome, although soluble fiber intake also enhances colonic SCFA production.