gut health

Could Your IBS Symptoms Be Caused by an Enzyme Deficiency? (SI)

Written by Jasmine Foster, BSc, BEd on March 19th, 2020

Sucrase-isomaltase is a digestive enzyme responsible for breaking down sucrose, maltose, and starch in the small intestine. If this enzyme doesn’t work right, it may contribute to symptoms of IBS. What do your genes have to do with it?

What is Sucrase-Isomaltase?

Sucrase-isomaltase is a digestive enzyme responsible for digesting sucrose (otherwise known as table sugar), starch, and maltose (a sugar found in grains). In the human body, it is found in the small intestine, where it breaks down sugars before they are absorbed into the bloodstream [R, R].

Sucrase-isomaltase (or SI) is essential for the digestion of most of our staple foods, but most people will never hear of it. Like so many other building blocks of our bodies, it only becomes medically relevant when it isn’t working right: people who have defective SI are said to have congenital sucrase-isomaltase deficiency, or CSID [R, R].

What is Congenital Sucrase-Isomaltase Deficiency?

People with CSID do not have functional SI enzymes and cannot digest sucrose, maltose, and starch. When they eat food containing these nutrients, they experience stomach cramps, bloating, gas production, and diarrhea. These problems can in turn cause malnutrition and impaired growth in children [R, R].

As far as we know, CSID is an autosomal recessive disorder, meaning that both copies of a person’s SI gene must be defective in order for them to suffer from CSID. There are currently four known variants that can cause CSID: Val577Gly (rs121912615), Gly1073Asp (rs121912616), Phe1745Cys (rs79717168), and Arg1124X (no RSID; this mutation causes the protein sequence to be shorter than normal). Any combination of these four mutations, as long as they are present on both copies of the SI gene, causes CSID [R, R, R].

Sucrase-isomaltase (SI) is a digestive enzyme that breaks down sucrase, maltose, and starch. When this enzyme doesn’t work correctly due to genetic mutations, it causes congenital sucrase-isomaltase deficiency, or CSID.

SI Variants and IBS

While defective SI is best known for causing CSID, it is possible that smaller reductions in SI activity could be responsible for some cases of IBS. In fact, one study of 1887 people found that SI variants were significantly more common in IBS patients than in matched controls [R].

The most significant mutation was rs9290264, which may reduce enzymatic activity by up to 35% compared to the SI enzyme without detrimental variants. This variant has been rated in the top 1% most deleterious changes in the human genome [R].

There are a number of other SI variants which may reduce enzyme activity; however, rs9290264 is the only one that has been confirmed in a lab setting so far [R].

Your SI Results for IBS

SNP Table

variant	genotype	frequency	risk allele
rs9290264
rs121912615
rs79717168

SNP Summary and Table

SI rs9290264

‘C’ = Normal sucrase-isomaltase; not associated with IBS
‘A’ = Possibly disrupted sucrase-isomaltase activity; associated with IBS

SI rs121912615

‘A’ = Normal sucrase-isomaltase
‘C’ = Defective sucrase-isomaltase; two copies cause CSID

SI rs79717168

‘A’ = Normal sucrase-isomaltase
‘C’ = Defective sucrase-isomaltase; two copies cause CSID

Recommendations

Hydration

It’s very important to make sure you are drinking enough water: dehydration has been found to significantly worsen the symptoms of IBS. Regardless of your symptoms, many experts recommend drinking 8 glasses of water per day, but a lot of research suggests that actual water requirements fluctuate hugely from day to day [R, R].

People who have difficulty digesting sucrose often have diarrhea after ingesting food that contains sugar, and dehydration is among the most common emergencies in CSID. If you have potentially detrimental SI variants and IBS, make sure you drink plenty of water every day [R].

Diet

People with CSID are typically advised to start an elimination diet that cuts sucrose out to as great a degree as possible. People with IBS and potentially detrimental SI variants may also want to try cutting down on their intake of sucrose [R, R, R].

In a low sucrose diet or a sucrose elimination diet, any food or drink sweetened with table sugar is eliminated. CSID patients are also advised to be very careful about their intake of starches and of certain fruits and vegetables. Eliminated foods include [R, R]:

Processed cheese (which may be sweetened with sugar)
Breads & cereals (which contain maltose)
Potatoes and sweet potatoes
Deli meats, gravies, and sausages
Sweetened drinks
Many fruits (apples, apricots, bananas, mangos, pineapples, etc.)
Many vegetables (beets, corn, carrots, onions, beans)

Among the foods always allowed on a low sucrose diet are [R, R]:

Unprocessed meat
Most nuts & seeds
Tofu
Dietary fats (butter, olive oil)
Milk
Diet beverages
Some fruits (avocado, cherries, figs, grapes, kiwis, pomegranate, etc.) [R]
Some vegetables (sprouts, asparagus, cauliflower, broccoli, mushrooms, etc.) [R]

While some foods may be added back into the diet after the elimination phase, this is a very challenging diet. To avoid nutritional deficiencies, it should be carefully supervised by a doctor or trained dietitian. Talk to your doctor before attempting this diet.

People with dysfunctional SI may have more difficulty digesting sucrose, maltose, and starch. A doctor or trained dietitian should supervise any attempt to eliminate these nutrients in the diet.

Supplements

One of the most likely causes of IBS is dysregulation of the gut flora. In fact, individuals with IBS often appear to have decreased diversity and numbers of beneficial microbiota and protective strains such as L. reuteri [R].

Saccharomyces boulardii is a type of yeast sometimes added to probiotic supplements. This yeast produces a highly efficient sucrase enzyme, and it may be included in the treatment plan of people (especially children) with diarrhea due to CSID. S. boulardii may be a promising probiotic for people with IBS and potentially detrimental SI variants [R].

Drugs

Sacrosidase (Sucraid) is a prescription drug that contains the sucrase enzyme. People with CSID take the enzyme with their meals so that they can safely consume some foods with sugar [R, R].

IBS-D is considered a possible misdiagnosis for some people who actually have CSID. There has also been some research into whether sacrosidase could be helpful for people who really do have IBS and not CSID [R].

If you have IBS that improves when you avoid sucrose and you have one or more potentially detrimental SI variants, you may want to talk to your doctor about whether sacrosidase could be appropriate for you. Do not start any new medication without your doctor’s instructions.

Jasmine Foster

BSc, BEd

Jasmine received her BS from McGill University and her BEd from Vancouver Island University.

Jasmine loves helping people understand their brains and bodies, a passion that grew out of her dual background in biology and education. From the chem lab to the classroom, everyone has the right to learn and make informed decisions about their health.

Disclaimer

The information on this website has not been evaluated by the Food & Drug Administration or any other official medical body. This information is presented for educational purposes only, and may not be used to diagnose or treat any illness or disease.

Also keep in mind that the “Risk Score” presented in this post is based only on a select number of SNPs, and therefore only represents a small portion of your total risk as an individual. Furthermore, these analyses are based primarily on associational studies, which do not necessarily imply causation. Finally, many other (non-genetic) factors can also play a significant role in the development of a disease or health condition — therefore, carrying any of the risk-associated genotypes discussed in this post does not necessarily mean you are at increased risk of developing a major health condition.

Always consult your doctor before acting on any information or recommendations discussed in this post — especially if you are pregnant, nursing, taking medication, or have been officially diagnosed with a medical condition.

More gut health blogs

Could This Gene Be Linked To Gut Inflammation? (ATG16L1) Could This Gene Play A Role In Inflammatory Bowel Disease? (STAT3) How Do Your Genes Respond to Dietary Fat? (TCF7L2) Do Your Genes Favor the Mediterranean Diet? (TCF7L2) How Does this Serotonin Receptor Affect Gut Inflammation? (HTR3E) The Impact of a Serotonin Receptor on IBS-D (HTR3A) How Can Neurotrophins Affect Gut Inflammation? (BDNF) Could Your IBS Symptoms Be Caused by an Enzyme Deficiency? (SI) What is the Connection Between β-Klotho and Gut Inflammation? (KLB) Can This Gene Worsen Gut Inflammation? (NOS2)

Content

What is Sucrase-Isomaltase? SI Variants and IBS Your SI Results for IBS

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