Effect of purified cellulose, pectin, and a low-residue diet on fecal volatile fatty acids, transit time, and fecal weight in humans

Abstract

Some relationships have been proposed between fecal volatile fatty acids, transit time, fecal weight, and dietary fiber intake. In this study, the effect of purified cellulose, purified pectin, and a natural low-residue diet on fecal acetic, propionic, butyric, isobutyric, valeric and isovaleric acids, transit time, and fecal weight was investigated. Forty-two healthy male and female adults were fed low-residue diets for 2 weeks, followed by 3 weeks on the same diet plus either 14 g/day cellulose or 6 g/day pectin or a sucrose placebo. Feces were collected for 7 days during weeks 2 and 5. From week 2 to 5, transit time decreased by 2.5 days with cellulose, 0.2 with placebo, and increased by 0.1 with pectin; fecal weight increased by 34 g/day with cellulose but decreased by 15 g/day with placebo and by 0.32 g/day with pectin (P < 0.05); volatile fatty acids decreased with placebo (-1.2 g/7 days), but increased with cellulose (+ 1.3 g/7 days) and pectin (+0.6 g/7 days) (P < 0.05). Volatile fatty acid changes with placebo and cellulose paralleled changes in fecal weight, thus fecal volatile fatty acid concentration did not change. Conversely, volatile fatty acid increase of the pectin group was not paralleled by fecal weight increase, signifying an increase in volatile fatty acid concentration (P < 0.05) of possible physiological significance. Some volatile fatty acids are probably absorbed, a fact worthy of further investigation. This study confirms: 1) that generalization of the effects of dietary fiber on volatile fatty acids, fecal weight and transit time should be avoided, 2) the mild antidiarrheal effect of pectin and, 3) the bulkung properties of cellulose. Am. J. Clin. Nutr. 33: 754-759, 1980.