Self-reported milk intolerance in irritable bowel syndrome: what should we believe?

The real importance of lactose malabsorption in irritable bowel syndrome (IBS) is still controversial. The aim is to define the relationship between patient perception of milk tolerance/intolerance, lactose malabsorption and abdominal symptoms in IBS.

A hydrogen breath test (HBT) after an oral load of lactose was carried out in 475 consecutive IBS patients, diagnosed according to the Rome criteria. Data were analyzed in 201 age- and sex-matched pairs of IBS patients, classified according to self-reported milk tolerance/intolerance. Hydrogen peak and excretion, predominant presenting symptom and the occurrence of symptoms during the test, were evaluated.

The prevalence of positive HBT and the occurrence of symptoms during the test was similar in milk "tolerant" (68.6%, 40.7% respectively) and "intolerant" patients (75.6%, 42.7% respectively), as well as peak (76.4 vs 75.2 ppm) and amount of H2 excreted (57.8 vs. 53.2 ppm/h). The positive predictive value for self-reported milk intolerance was 0.75, and the negative predictive value in regular milk users was 0.31, reflecting the prevalence of lactose malabsorption in the general population more than the awareness of milk tolerance.

In IBS patients, self-reported milk intolerance does not help in identifying lactose malabsorbers. The opposite does not rule out the occurrence of symptoms after a lactose load. Lactose is, indeed, responsible for symptoms in some IBS patients, however, these patients can only be identified by the occurrence of symptoms during the test, and not on the individual perception of milk intolerance.