csid 101

What you should know about congenital sucrase-isomaltase deficiency (CSID)

CSID is clinically known as Congenital Sucrase-Isomaltase Deficiency. Diagnosed in infancy, the deficiency was thought to be extremely rare. The affected child would have to receive a mutated recessive gene from both parents for it to be expressed. Thanks to advances in genetics, we now know that symptomatic carriers exist and that there are many different mutations.

This disease resembles unresolved IBS (irritable bowel syndrome), and some patients may even think they have a sugar allergy. This condition is not an allergy; no immune response is mounted in the presence of sucrose. It is truly an intolerance and is sometimes called sugar or sucrose intolerance.

This genetic disorder results in a deficiency of the enzyme sucrase-isomaltase. The disaccharidase sucrase is required to cleave sucrose into glucose and fructose for absorption into the bloodstream. In the absence of sucrase, the intact sugar (sucrose) cannot be absorbed and passes into the large intestine where it is fermented and produces gastrointestinal (GI) symptoms.

Symptoms of CSID include gas, bloating, abdominal pain, or chronic watery diarrhea after meals and snacks containing sugar (sucrose) and starch. Symptoms can range from mild to severe depending on the type of mutation and the amount of enzyme activity. Also, because of the inconsistency in the type and amount of sugar and starch consumed in the diet, symptoms may vary from day to day.

Since the symptoms are so similar to other digestive diseases, CSID is often misdiagnosed. But multiple testing methods aid in the diagnosis of CSID. The disaccharidase assay (tissue biopsy), which is the gold standard, the free sucrose breath test, or the 4-4-4 sugar challenge can all assist health care providers in making the diagnosis.

Treatment consists of pharmaceutical therapy, as well as a low-sucrose, low-starch diet. A dietitian is critical in helping the patient navigate the diet to maximize the benefits of pharmaceutical therapy and help alleviate symptoms.

Do you have sugar intolerance?

If you think you may be suffering from Sugar Intolerance (Sucrose Intolerance, Congenital Sucrase-Isomaltase Deficiency, or CSID), you can try a simple food challenge. It is called the 4-4-4 Sugar Challenge. Follow these three simple steps:

Step 1

Stir 4 tablespoons of ordinary table sugar into a 4-ounce glass of water. Mix until sugar is completely dissolved.

Step 2

Drink it on an empty stomach.

Step 3

See if symptoms, such as bloating, gas, and diarrhea, occur during the next 4 to 8 hours. If so, this suggests sugar intolerance is possible.


1. You may have relatively  SEVERE SYMPTOMS. If you do have sucrose intolerance, this challenge may cause relatively severe gas, bloating, and diarrhea. Please plan to take the challenge on a weekend or other day when GI symptoms will not cause you to miss work or other important events.

2. THIS CHALLENGE SHOULD NOT BE GIVEN TO INFANTS, VERY YOUNG CHILDREN, TO PEOPLE WITH SEVERE SYMPTOMS, OR THOSE WHO ARE DIABETIC. You and your doctor should take into account personal health considerations.

3. THIS IS NOT A DIAGNOSTIC TEST and cannot be used to confirm sucrose intolerance. Only a doctor can tell you if your symptoms are caused by CSID.