Disaccharidase deficiency

Your small bowel produces a group of enzymes called disaccharidases — lactase, sucrase-isomaltase, maltase, and others — that break down disaccharide sugars (lactose from milk, sucrose from regular table sugar, maltose from grains) into smaller monosaccharide sugars that your body can absorb. When one or more of these enzymes are missing or working poorly, the undigested sugar passes into the large bowel, where bacteria ferment it. This produces gas, draws water into the bowel, and causes the classic symptoms of bloating, abdominal pain, excess wind, and diarrhoea — usually within a few hours of eating the trigger food.

If you have been told you have IBS but the standard advice has not really helped, a disaccharidase deficiency is one of the conditions worth considering. It is more common than people realise — and unlike IBS, it is a specific, measurable diagnosis with a clear treatment.

Disaccharidase deficiencies fall into three broad categories:

• Primary (congenital) disaccharidase deficiencies — present from birth, due to an inherited fault in the gene that codes for the enzyme. The most common is congenital sucrase-isomaltase deficiency (CSID), which is increasingly recognised in adults whose symptoms have long been put down to IBS. Congenital lactase deficiency is rare.
• Adult-onset lactase deficiency — by far the most common disaccharidase issue worldwide. The enzyme lactase, which breaks down the sugar in milk (lactose), naturally declines from late childhood onwards in most of the world's population. This is the normal biological pattern for the majority of adults — not a 'disease' as such — but it can cause real symptoms with dairy.
• Secondary (acquired) disaccharidase deficiencies — temporarily reduced enzyme activity due to damage to the small bowel lining. Common causes are coeliac disease, Crohn's disease, gastroenteritis, and bacterial overgrowth. The deficiency usually improves once the underlying condition is treated, but it can persist.

Symptoms tend to be similar regardless of which enzyme is affected — what differs is the trigger food. Common patterns include:

• Bloating that develops within 1–3 hours of eating
• Excessive wind
• Abdominal cramping or pain
• Diarrhoea, sometimes urgent
• A 'gurgling' or 'rumbling' abdomen
• Often a clear pattern with specific foods — milk and dairy (lactose), sugary or starchy foods (sucrose, maltose), or both

For many patients, the symptoms have been long-standing and variously attributed to IBS, food sensitivities, or a generally 'sensitive stomach'. The clue is the temporal link to specific foods — and the fact that standard IBS advice has not really helped.

Diagnosis is best made by directly measuring enzyme activity in a small biopsy of the small bowel lining, taken during a routine gastroscopy. The biopsy is sent to a specialised laboratory where the activity of each disaccharidase enzyme is measured. This is called a disaccharidase assay, and it is the gold-standard test for these conditions.

Breath tests (for example, hydrogen breath testing for lactose intolerance) are an alternative for some specific deficiencies and can be done first if only one enzyme is suspected — but the duodenal biopsy is the most comprehensive option, particularly when the picture is not clear-cut.

The gastroscopy itself is a short, well-tolerated day procedure under sedation. The biopsies cause no discomfort and add no extra time to the procedure.

Treatment depends on which enzyme is affected, and on whether the cause is primary (lifelong) or secondary (linked to another condition). For most patients the approach is straightforward:

• Dietary modification — limiting or avoiding the relevant sugar. For lactase deficiency, this means reducing dairy or switching to lactose-free options. For sucrase-isomaltase deficiency, it means moderating sucrose and starch intake. A dietitian with experience in this area is invaluable for getting the balance right and avoiding unnecessarily restrictive eating.
• Enzyme replacement — for some deficiencies, the missing enzyme can be taken as a supplement with meals. Lactase tablets (widely available without prescription) work well for lactose intolerance. Sacrosidase is available for sucrase-isomaltase deficiency.
• Treating any underlying cause — for acquired (secondary) deficiencies, managing the bowel condition that caused the enzyme damage often allows the enzyme activity to recover.

The improvement once the right approach is found is often dramatic. Many patients describe feeling like a different person.

Mr Nguyen performs gastroscopy with duodenal biopsies for disaccharidase assay at Warringal Private Hospital and Epworth Eastern. The biopsies are sent to a specialist laboratory and the results are usually back within 2–4 weeks. He will discuss the results with you at a follow-up appointment, and where a deficiency is identified, refer you to a dietitian experienced in this area for tailored advice. Where the deficiency is secondary to another bowel condition (such as coeliac disease or Crohn's), management is coordinated with your gastroenterologist or GP.

Consider asking your GP for a referral if you have ongoing bloating, gas, abdominal pain, or diarrhoea — particularly if there is a clear food trigger, the symptoms started after a bout of gastroenteritis or another bowel illness, or standard 'IBS' management has not made a meaningful difference. These conditions are commonly missed, and the relief that comes from identifying them is significant.

Your GP will send a referral and most patients are seen within one to two weeks. At the consultation a careful history is taken — particularly about food triggers and symptom patterns — and whether a gastroscopy with disaccharidase biopsy is the right next step will be discussed with you. The procedure itself is straightforward and is described in detail on the Gastroscopy procedure page. A follow-up appointment is arranged once results are back to discuss the findings and the next steps in management.