Digestive enzymes (alpha-galactosidase, lactase)

Digestive enzyme supplements come in two kinds. Targeted enzymes do one job: alpha-galactosidase (sold under names like Beano) splits the galacto-oligosaccharides in beans, lentils, and some vegetables before they reach the colon, and lactase splits the lactose in milk. Broad “digestive enzyme blends” containing proteases, lipases, and amylases are marketed for general digestion; they have not been tested in IBS trials, and the evidence below concerns the targeted enzymes only.

Alpha-galactosidase has one trial in IBS, from the Monash University group that developed the low FODMAP diet. Thirty-one patients who produced hydrogen on breath testing went through a double-blind crossover in which, after a three-day low FODMAP run-in, they ate provided meals high in GOS for three days with a full-dose enzyme (300 GALU), a half-dose, or placebo. The high-GOS meals raised symptoms in 21 of the 31, and in those GOS-sensitive patients the full dose reduced the rise in overall symptoms (median 24.5 mm on placebo versus 5.5 mm with enzyme on a 100 mm scale) and in bloating (20.5 versus 6.5 mm), while breath hydrogen did not differ PMID 28809383. An earlier Italian study gave eight healthy volunteers a 420 g bean meal with 300 or 1,200 GalU of enzyme or placebo; the higher dose reduced breath hydrogen and flatulence severity, and both doses lowered the total symptom score, but these were volunteers without IBS PMID 17151807.

Lactase is different because the underlying condition, lactose malabsorption, is common and well understood. A 2019 review in Gut explains that symptoms after lactose depend on the dose, how much lactase the gut makes, and the microbiome, and that people with visceral hypersensitivity or IBS are more likely to get symptoms from lactose regardless of how well they digest it. The review lists a low-lactose diet, lactase supplements, and prebiotic-driven colonic adaptation as management options, and describes their clinical outcome as modest because lactose is only one of several poorly absorbed carbohydrates that cause symptoms by the same mechanism PMID 31427404. Both NICE and the BSG say hydrogen breath testing for lactose intolerance is not needed to confirm IBS, the BSG adding that rapid transit in IBS can make the test falsely positive PMID 33903147.

Points clinicians commonly raise: an enzyme can only help with the carbohydrate it targets, so alpha-galactosidase does nothing for lactose, fructans, or polyols, and lactase does nothing for beans; the practical use is to make a specific food tolerable rather than to change IBS overall; in the Monash trial the enzyme only mattered in the two-thirds of patients who were sensitive to GOS in the first place; and these products are cheap and low-risk, which is a reason to test one against a known trigger meal rather than to take it daily.

Talk to a clinician before starting or stopping anything.