Oral xylose isomerase decreases breath hydrogen excretion and improves gastrointestinal symptoms in fructose malabsorption – a double-blind, placebo-controlled study


Correspondence to:

Prof. Dr P. Komericki, Department of Environmental Dermatology and Venereology, Medical University of Graz, Auenbruggerplatz 8, 8036 Graz, Austria.

E-mail: peter.komericki@medunigraz.at



Incomplete resorption of fructose results in increased colonic hydrogen production and is a frequent cause of abdominal symptoms. The only treatment available is diet.


To study whether orally administered xylose isomerase (XI), an enzyme that catalyses the reversible isomerisation of glucose and fructose, can decrease breath hydrogen excretion in patients with fructose malabsorption.


Patients received 25 g fructose in 100 mL water together with either placebo or XI capsules. Primary endpoint was the reduction in breath hydrogen excretion, as assessed by the area under the breath hydrogen curve over 4 h (AUC). A secondary endpoint was the reduction in abdominal pain, bloating and nausea assessed on a visual analogue scale (VAS, range: 0–10). A P value <0.05 was considered statistically significant.


Sixty-five patients in whom fructose malabsorption had been diagnosed by positive breath hydrogen test within the previous year, were included in the study [15 males, 50 females; mean age 43.3 (s.d. = 14.4), range: 21–73 years]. The median AUC was 885 ppm/240 min in the XI group compared to 2071 ppm/240 min in the placebo group (P = 0.00). Median scores for abdominal pain (0.7 vs. 1.3) and nausea (0.2 vs. 0.6), but not for bloating (P = 0.053), were significantly improved after XI (P = 0.009 and P = 0.005) as compared with placebo.


Oral administration of xylose isomerase significantly decreased breath hydrogen excretion after ingestion of a watery fructose solution. Nausea and abdominal pain were significantly improved by xylose isomerase.