Clinical impact of identifying lactose maldigestion or fructose malabsorption in irritable bowel syndrome or other conditions

South Med J. 2009 Oct;102(10):1010-2. doi: 10.1097/SMJ.0b013e3181b64c7f.


Background: The role of carbohydrate maldigestion or malabsorption remains unclear in patients with irritable bowel syndrome (IBS). The purpose of this study was to examine the impact of identifying lactose maldigestion (LM) and fructose malabsorption (FM) on patients with and without IBS.

Methods: Patients who received lactose and fructose challenge testing formed the study group. Carbohydrate challenge testing was performed with 50 g lactose and 25 g fructose. Breath samples were collected and analyzed for hydrogen, methane, and CO2 (for correction) using a MicroLyzer Model SC (QuinTron Instrument Company, Milwaukee, WI). Questionnaires were used to assess Rome III IBS criteria, compliance with carbohydrate dietary modifications, and changes in symptoms.

Results: One hundred and twenty-one of the 181 (67%) study subjects were able to be contacted 8 months to 4 years after carbohydrate testing. LM (21) and FM (2) were seen in 33% of the 66 IBS subjects. LM (12) and FM (9) were seen in 33% of the 55 subjects without IBS. Seventy-seven percent of IBS and 72% of those without IBS reported compliance with dietary advice. Of the subjects who reported compliance, 47% of IBS and 77% of those without IBS reported that, after identifying LM or FM, their symptoms resolved or improved.

Conclusions: Carbohydrate maldigestion has a similar incidence in patients with and without IBS and both populations have similar compliance with therapeutic diets. However, patients without IBS are more likely to have improvement in symptoms when dietary changes are instituted when compared to IBS patients.

MeSH terms

  • Breath Tests
  • Female
  • Follow-Up Studies
  • Fructose / pharmacokinetics*
  • Humans
  • Intestinal Absorption / physiology*
  • Irritable Bowel Syndrome / diet therapy
  • Irritable Bowel Syndrome / physiopathology*
  • Lactose
  • Lactose Intolerance / physiopathology*
  • Male
  • Patient Compliance
  • Sweetening Agents
  • Treatment Outcome


  • Sweetening Agents
  • Fructose
  • Lactose