Effect of a Fructose and Lactose Elimination Diet in Patients with Irritable Bowel Syndrome: A Randomized Double-Blind Placebo-Controlled Study

Katharina Moritz, Wolfgang Hemmer, Peter Jung, Gabriele Sesztak-Greinecker, Manfred Götz, Reinhart Jarisch, Felix Wantke


AIM: Current data on the impact of carbohydrate maldigestion on symptoms in patients with irritable bowel syndrome (IBS) are conflicting. The aim of the present study was to investigate in a randomized double-blind placebo controlled manner whether a lactose or fructose elimination diet can improve symptoms of IBS. METHODS: 320 patients with IBS were first randomized to a fructose or lactose-free diet for 3 weeks. Stool frequency and consistency and gastrointestinal complaints were recorded before and after the diet phase using a standardized questionnaire including visual analogue scales for severity of abdominal pain, number of days with abdominal pain, bloating and flatulence, contentment and impairment in quality of life. Subsequent to the diet phase, patients were examined for fructose or lactose malabsorption by H2 breath testing. RESULTS: Of 221 patients completing the study (40 males, 181 females), 111 had a positive breath test to fructose (group 1), 12 to lactose (group 2), 72 to both fructose and lactose (group 3), and 26 patients were negative in both tests (group 4). In group 1, the mean symptom score decreased from 313±69 before the diet to 178±100 after the diet (-135±100, p<0.0001) under fructose-free diet (verum), and from 326±65 to 197±104 (-129±111, p<0.0001) under lactosefree diet (placebo). Also in the other groups (including patients with a negative breath test to both carbohydrates), both diets lead to a comparable decrease in total symptom scores (mean drop -40±10%, p<0.05 to p<0.0001) without significant differences between fructoseand lactose-free diet. CONCLUSION: Although a great proportion of IBS patients show impaired absorption of fructose or lactose in H2 breath tests, the clinical effect of the corresponding verum diets was not superior to that of placebo diets. The results suggest that clinical improvement in IBS patients following elimination diets is largely due to placebo effects.


Irritable bowel syndrome; Fructose malabsorption; Lactose malabsorption; Placebo effect

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