Is Sucrase-Isomaltase Deficiency the cause of your IBS?

Carbohydrates make up about half of an average person's diet, and come in the form of both simple and complex sugars. Monosaccharides (such as glucose and fructose) and disaccharides (such as sucrose, maltose, and lactose) are simple sugars, while complex sugars include starches, glycogen, and fibres, which are made up of multiple glucose molecules arranged in different structures.

Normal digestion

For the body to absorb carbohydrates, they must be broken down into tiny units. Disaccharides and polysaccharides (like starches) need to be hydrolyzed (digested) into monosaccharides. Starch digestion begins in the mouth with the help of salivary amylase, and then continues with pancreatic amylase, which eventually breaks down starch into smaller sugar units, maltose and sucrose.

In the final stage of starch digestion, digestive enzymes called disaccharidases in the brush border of the small intestine hydrolyze disaccharides (such as maltose and sucrose) into monosaccharides (such as glucose and fructose), which are then absorbed into the bloodstream for metabolism.

Disaccharidase enzymes and their actions

Sucrase-Isomaltase: This enzyme digests most of the sucrose and about 60-80% of the maltose.

What is Sucrase-Isomaltase Deficiency?

Sucrase-Isomaltase Deficiency (SID) is a condition characterised by absent or reduced activity of the sucrase-isomaltase disaccharide enzyme. It can either be congenital, meaning it's present at birth due to gene defects, or it can develop later in life, known as a secondary disaccharidase deficiency (SDD).

Secondary disaccharidase deficiency

SDD can develop from generalised intestinal damage related to a number of causes involving villous atrophy, infection, and/or rapid G.I. transit.

It is important to note that SDD can be transient, with enzyme activity returning to normal as the underlying disorder resolves.

Potential causes of SDD include:

• Coeliac disease

• Nontropical sprue

• Inflammatory bowel disease

• Chemotherapy

• Acute gastroenteritis

• Giardiasis

• Tropical sprue

• SIBO or Dysbiosis

• Rapid gastric emptying

• Dumping syndrome

• Medications

Maldigestion = digestive symptoms

Because there is a lack or absence of disaccharidase enzymes, carbohydrate maldigestion occurs, resulting in non-absorbed carbohydrates entering the distal small intestine and colon. In turn, these undigested carbs are fermented by gut bacteria, leading to both excess gas production and short-chain fatty acid production. This can then cause:

• Bloating / abdominal distention

• Abdominal discomfort/pain/cramps

• Excessive flatulence

• Diarrhoea / loose stools

• Less common: Nausea; dyspepsia

• Inadequate growth

• Involuntary weight loss

Symptoms vary depending on the amount of sugar and starches being consumed and individual tolerance levels.

Differential Diagnosis

Sucrase-Isomaltase Deficiency should be considered in patients with diarrhoea-predominant IBS, particularly those not responding to the low FODMAP diet.

Testing for Sucrase Isomaltase Deficiency

The gold standard for testing and diagnosing intestinal disorders associated with SID is endoscopic small intestine biopsies assayed for disaccharidase activity.

Normal Disaccharidase values

The dietary management of Sucrase Isomaltase deficiency

1. Dietitian - It is essential that you work with a dietitian or gastroenterologist who is experienced in managing this condition. Your Dietitian will help you manage your gut symptoms via navigating your dietary intolerances and triggers, as well as provide guidance on how to meet your nutrient requirements. They may also recommend supplements if required.

2. Food-symptom Diary - Your dietitian will get you to keep a food-symptom diary to help you identify trigger foods.

3. Dietary restriction/elimination of sucrose - You will be educated and guided to follow a Sucrose-free diet. This is generally followed for 2-4 weeks, or until symptoms have ceased or you have had an overall improvement in G.I symptoms.

4. If your symptoms persist after following a sucrose-free diet, you will be guided to also reduce/limit your starch intake - This means you will be instructed to follow a Sucrose-free + limited/completely starch-free diet.

5. Challenge Phase: If symptoms have improved after 4 weeks, restricted foods will slowly be reintroduced to test tolerance levels.

Usually, the intestinal cells are producing a limited amount of disaccharidase enzyme, and small doses of foods containing disaccharides can be processed.

Symptoms will be triggered when the dose of disaccharide-containing food exceeds your enzyme's capacity to digest it.

The goal is to determine your own personal limits, remain symptom-free, and liberalize your diet as much as possible.

Other Considerations

• Strategies for improving starch tolerance include: Chewing foods slowly to maximise salivary amylase exposure + eating starches with greater fibre content (such as rolled oats, barley, brown rice, and whole-grain flour) to prolong exposure to amylase throughout the GI tract.

• Nutritional adequacy / substitute foods to continue to meet your nutrient needs

• Understanding food labels: Starch can be calculated by: Starches = Total carbohydrates – sugars - fibre

• Enzyme replacement therapy – Sacrosidase = allows liberalisation of the sucrose-restrictive diet. This enzyme is derived from baker's yeast (saccharomyces cerevisiae). This supplement is usually taken with each meal/snack.

• Nutritional supplements to consider: calcium, vitamin D, vitamin C, B complex

In summary

Sucrase-isomaltase deficiency is a condition that affects the ability to digest certain carbohydrates leading to IBS symptoms. The dietary management of SID involves eliminating sucrose from the diet and limiting starch intake. Chewing food slowly and consuming starches with more fibre can improve starch tolerance. Enzyme replacement therapy and nutritional supplements may also be considered. Reintroducing restricted foods in small doses can help determine personal limits and liberalise the diet.

References

doi: 10.1007/s11136-021-02819-z; Congenital Sucrase-Isomaltase Deficiency: What, When, and How?: Gastroenterology & Hepatology Volume 16, Issue 10, Supplement 5 October 2020