CSID and SIBO: Is There a Link?

Congenital sucrase-isomaltase deficiency (CSID) and small intestinal bacterial overgrowth (SIBO) are digestive conditions that cause uncomfortable digestive symptoms.

Because these digestive symptoms tend to overlap, you may wonder whether one leads to the other and vice versa.

This article explains everything you need to know about the link between CSID and SIBO.


What is CSID?

CSID is a congenital (inherited) disorder caused by a mutation in the sucrase-isomaltase (SI) gene.

This mutation leads to a deficiency in the enzymes sucrase and isomaltase.

Sucrase is necessary to digest sucrose — or table sugar — while isomaltase is needed to digest isomaltose — a type of starch.

With low or no levels of these enzymes, sugar and starch travel through your small intestine undigested, causing various digestive symptoms.

CSID symptoms include (1):

  • stomach pain
  • excessive gas
  • reflux
  • bloating
  • diarrhea
  • nausea
  • constipation

A deficiency in sucrase, isomaltase, or both, can also be caused by inflammatory conditions that affect the small intestine like celiac disease and Crohn’s disease.

When this occurs, it’s known as secondary or acquired sucrase-isomaltase deficiency (SID), which is much more common than the congenital form.

The treatment for CSID and SID involves the life-long dietary restriction of sucrose and isomaltose.

But following a CSID diet can be challenging since so many foods contain sugar and starch.

People with CSID can take a prescription medication called Sucraid (sacrosidase) — an enzyme replacement for sucrase — to allow more diet flexibility but it doesn’t contain isomaltase.


CSID is an inherited condition characterized by the inability to digest sucrose (table sugar) and isomaltose (starch). The inability to digest sugar and starch can also occur in people with digestive inflammatory conditions.

What is SIBO?

SIBO is a condition in which excess bacteria inhabit the small intestine.

SIBO is believed to develop when bacteria pass from the large intestine into the small intestine, which normally contains few bacteria (2).

Low stomach acid levels, slow passage of food through the small intestine, and a weakened immune system may also lead to SIBO.

SIBO symptoms include:

  • abdominal pain
  • bloating
  • excessive gas
  • diarrhea
  • indigestion
  • brain fog

Antibiotics are commonly prescribed to treat SIBO, but they aren’t always effective and can promote the development of antibiotic-resistant organisms and infections (3).

A low-FODMAP diet has been shown to improve SIBO symptoms (3).

FODMAP stands for fermentable oligo-, di-, and monosaccharides and polyols.

These are carbohydrates that are poorly absorbed and easily fermented by gut bacteria.

An elemental diet — which consists of nutritionally complete formulas that contain pre-digested nutrients — has also shown some success in alleviating SIBO symptoms (4).


SIBO is a condition in which excess bacteria inhabit the small intestine, which normally contains very few bacteria. Antibiotics are commonly prescribed to treat SIBO but it can also be managed with a low-FODMAP or elemental diet.

SIBO may lead to sucrose intolerance

Anyone can experience SIBO, but it’s more common in people with (3):

People with CSID can also experience SIBO.

In one report, a 50-year-old woman was diagnosed with SIBO after she complained of intermittent bloating, non-bloody diarrhea, and excessive gas for six months, and after the doctors ruled out other potential conditions (4).

She was treated with an antibiotic for 14 days but only experienced partial relief.

After further testing, the doctors determined she had CSID. They referred her to a dietitian and prescribed her Sucraid, causing a complete resolution of her symptoms.

While this is just a case report, it suggests that SIBO and CSID can occur simultaneously.

SIBO is less likely to cause CSID since CSID is inherited but it’s possible that acquired forms of sucrose intolerance that develop due to other digestive conditions like H. pylori infection, celiac disease, and Crohn’s disease can lead to SIBO.

Sucrase intolerance and CSID also commonly coexist with irritable bowel syndrome (IBS).

Two large observational studies found that people with CSID are more likely to develop IBS (5, 6).

These are important findings since research suggests that nearly 40% of people but up to 84% with IBS have SIBO (7).


SIBO likely doesn’t cause CSID but SIBO may cause sucrase intolerance that occurs due to inflammatory digestive conditions like H. pylori infection, celiac disease, and Crohn’s disease.

Identifying sucrose intolerance with SIBO or IBS

Sucrose intolerance — whether congenital or acquired — is commonly underdiagnosed since it causes digestive symptoms that are confused with IBS and SIBO (4).

A low-FODMAP diet can improve digestive symptoms if you have IBS, SIBO, or both.

However, a low-FODMAP diet does not restrict sucrose, so if you don’t experience symptom improvement on a low-FODMAP diet, consider getting tested for sucrose intolerance (8).

The disaccharidase assay is the gold standard for diagnosing a sucrase deficiency (8).

The assay or test measures levels of five digestive enzymes obtained from a sample of your small intestine.

But due to its invasiveness, a sucrose breath test — which you can do at home — is an acceptable alternative.

If you are sucrose intolerant, you will need to restrict it from your diet.

The prescription medication Sucraid replaces what your body doesn’t naturally make — allowing more diet flexibility — but it has only been tested in people with acquired sucrase deficiency.


The symptoms of sucrose intolerance — whether congenital or acquired — overlap with IBS, leaving sucrose intolerance to be commonly underdiagnosed. Consider testing for sucrose intolerance if your SIBO or IBS symptoms don’t improve on a low-FODMAP diet.

The bottom line

CSID is an acquired condition characterized by the inability to digest sucrose and isomaltose.

More common is sucrose intolerance which occurs due to the presence of an inflammatory digestive condition like H. Pylori, celiac disease, or Crohn’s disease.

Although CSID symptoms overlap with SIBO — which occurs when excess bacteria inhabit the small intestine — it’s unlikely that SIBO leads to CSID.

However, people with CSID are more likely to develop IBS, which commonly occurs alongside SIBO.

Following a low-FODMAP diet can improve IBS and SIBO symptoms but it does not restrict sucrose.

Therefore, if you have IBS or SIBO but are not experiencing symptom relief on a low-FODMAP diet, consider getting tested for sucrose intolerance.

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