Effects of inulin and lactose on fecal microflora, microbial activity, and bowel habit in elderly constipated persons

Am J Clin Nutr. 1997 May;65(5):1397-402. doi: 10.1093/ajcn/65.5.1397.


Constipation is an ailment encountered often in elderly people. A study was initiated to test the effects of lactose or inulin on the bowel habits of constipated elderly patients and to correlate these effects with several variables measured in feces such as microflora composition, concentration of lactate and short-chain fatty acids (SCFAs), pH, and the activities of beta-glucosidase and beta-glucuronidase, Groups of 15 and 10 patients received lactose and inulin, respectively, for a period of 19 d. The dose, 20 g/d from days 1 to 8, was gradually increased to 40 g/d from days 9 to 11 and was kept at this dose from days 12 to 19. There was considerable interindividual variations with this kind of dietary intervention. Inulin increased bifidobacteria significantly from 7.9 to 9.2 log10/g dry feces, but decreased enterococci in number and enterobacteria in frequency. In individuals consuming lactose, a noticeable increase in fecal counts of enterococci and a decrease in lactobacilli and clostridia was detected. Total bacterial counts remained unchanged. No changes in the concentrations of fecal SCFAs and lactate were observed. SCFAs showed a slight trend toward higher molar ratios of acetate to butyrate in response to the intake of lactose or inulin. The fecal pH and the beta-glucosidase and beta-glucuronidase activities were not influenced by sugar intake. Inulin showed a better laxative effect than lactose and reduced functional constipation with only mild discomfort.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Bifidobacterium / cytology
  • Cathartics / therapeutic use*
  • Colony Count, Microbial
  • Constipation / drug therapy*
  • Enterobacteriaceae / cytology
  • Enterococcus / cytology
  • Fatty Acids / analysis
  • Feces / chemistry
  • Feces / microbiology*
  • Female
  • Glucuronidase / metabolism
  • Humans
  • Hydrogen-Ion Concentration
  • Inulin / administration & dosage
  • Inulin / therapeutic use*
  • Lactic Acid / analysis
  • Lactose / administration & dosage
  • Lactose / therapeutic use*
  • beta-Glucosidase / metabolism


  • Cathartics
  • Fatty Acids
  • Lactic Acid
  • Inulin
  • beta-Glucosidase
  • Glucuronidase
  • Lactose