Improved clinical tolerance to chronic lactose ingestion in subjects with lactose intolerance: a placebo effect?

Gut. 1997 Nov;41(5):632-5. doi: 10.1136/gut.41.5.632.


Background: Uncontrolled studies of lactose intolerant subjects have shown that symptom severity decreases after chronic lactose consumption. Adaptation of the colonic flora might explain this improvement.

Aims: To compare the effects of regular administration of either lactose or sucrose on clinical tolerance and bacterial adaptation to lactose.

Methods: Forty six lactose intolerant subjects underwent two 50 g lactose challenges on days 1 and 15. Between these days they were given 34 g of lactose or sucrose per day, in a double blind protocol. Stool samples were obtained on days 0 and 14, to measure faecal beta-galactosidase and pH. Symptoms, breath H2 excretion, faecal weight and electrolytes, and orofaecal transit time were assessed.

Results: Except for faecal weight, symptoms were significantly milder during the second challenge in both groups, and covariance analysis showed no statistical difference between them. In the lactose group, but not in the sucrose group, faecal beta-galactosidase activity increased, pH dropped, and breath H2 excretion decreased.

Conclusion: Bacterial adaptation occurred when lactose intolerant subjects ingested lactose for 13 days, and all symptoms except diarrhoea regressed. Clinical improvement was also observed in the control group which displayed no signs of metabolic adaptation. This suggests that improved clinical tolerance may be just a placebo effect.

Publication types

  • Clinical Trial
  • Controlled Clinical Trial

MeSH terms

  • Adult
  • Bacteria / metabolism
  • Breath Tests
  • Colon / microbiology
  • Double-Blind Method
  • Feces / enzymology
  • Female
  • Humans
  • Hydrogen / analysis
  • Hydrogen-Ion Concentration
  • Lactose / administration & dosage*
  • Lactose Intolerance / enzymology
  • Lactose Intolerance / microbiology
  • Lactose Intolerance / therapy*
  • Male
  • Middle Aged
  • Placebo Effect
  • Sucrose / administration & dosage*
  • beta-Galactosidase / analysis


  • Sucrose
  • Hydrogen
  • beta-Galactosidase
  • Lactose