What Are the Symptoms of CSID?

In general terms, when someone with CSID eats sucrose, he/she is unable to digest the sucrose and the person develops gastrointestinal (GI) symptoms. Most patients with CSID have very little or absent sucrase, which is the enzyme needed for sucrose digestion. Patients with CSID also have varying amounts of the enzymes required for starch digestion (isomaltase, palatinase, maltase), so these patients may also experience gastrointestinal symptoms from starch consumption.


Gastrointestinal symptoms for patients with CSID can vary from mild to severe. Gastrointestinal symptoms occur because dietary sucrose moves through the small intestine undigested. The undigested sugar load enters the colon and bacteria feed off the increased amount of sugar that causes fermentation, which results in diarrhea and an increase in gas production. Diarrhea occurs when substances are not absorbed in the colon and retain water. This is referred to as osmotic diarrhea. Presenting symptoms may differ between infants, children, and adults.



Infants and Children

Infants do not manifest symptoms of CSID until they begin to ingest sucrose- and starch-containing foods (e.g., juices, solid foods, formula, and medications sweetened with sucrose). Infants who are exclusively breastfed may not show symptoms until the introduction of solid foods or until weaning. Common symptoms are chronic, watery diarrhea with or without failure to thrive (poor physical growth) and abdominal pain. Pediatric patients may also present with abdominal swelling (distension), gassiness, colic, irritability, excoriated buttocks (abrasions and irritations), diaper rash, and vomiting. A minority of patients may require hospitalization due to dehydration, malnutrition, muscle wasting, and weakness. Because children have shorter GI tracts, their symptoms may be more severe than adults.

Some children with CSID are not diagnosed as infants and are presumed to have chronic, nonspecific diarrhea (toddler’s diarrhea). In older children, symptoms include abdominal pain, cramps, gas, and intermittent diarrhea. They may be diagnosed with irritable bowel syndrome (IBS). In older children, a prolonged period of misdiagnosis may occur where patients learn to live with their symptoms. The potential reasons for a delay in the diagnosis of CSID could be mistaken diagnoses of milk protein intolerance, food allergies, and chronic, nonspecific diarrhea. CSID is a genetic disease that patients will not “outgrow.”




Adult symptoms are similar to infants and children, but may be less severe due to their longer GI tract. In adults, a prolonged period of misdiagnosis may occur when the patient “learns to live with” their uncomfortable gastrointestinal symptoms, or assumes their ongoing GI problems to be “normal.” Recurrent symptoms similar to those caused by CSID, such as frequent bowel movements, chronic diarrhea, unexplained abdominal pain, gassiness, bloating, weight loss, abdominal distention, and vomiting should not be ignored. In some adults, symptoms may be limited to an increase in bowel frequency, abdominal distention, and flatulence, even though episodic watery diarrhea upon ingestion of high levels of sucrose may occur. In some patients, diarrhea may alternate with constipation, leading to a misdiagnosis of irritable bowel syndrome (IBS). Consultation with a gastroenterologist is recommended to discuss any recurring, persistent gastrointestinal symptoms.


Failure to absorb dietary sucrose and starch may impact the absorption of other nutrients and the hormonal regulation of gastrointestinal function. Unabsorbed carbohydrates slow down gastric emptying and accelerate small-intestinal transit time which contributes to malabsorption of starch, fat, and monosaccharides. Severity of symptoms is affected by the quantity of sucrose and starch consumed, colonic bacterial activity, the absorptive capacity of the colon, the rate of gastric emptying, and small bowel transit time.