Sugar Intolerance... do you have it?

Updated: Apr 5

A condition known as congenital suscrase-isomaltase deficiency (CSID) results in a person having the inability to digest certain sugars. This is a genetic disorder and people who suffer from it are unable to break down the sugars, sucrose and maltose, as well as other carbohydrates made from these simple sugar molecules.

Sucrose is a very common simple carbohydrate that is found in fruits and table sugar. Therefore any processed product containing table sugar (white, raw, brown, etc), will not be digested properly by people with CSID.

Maltose is another simple sugar that is found in grains. The same goes for this sugar, those with CSID cannot properly digest it.

Both sucrose and maltose are types of carbohydrates known as disaccharides (carbohydrates made of two simple sugars). During digestion, disaccharides are broken down into their simple (single) unit forms. This allows them to be small enough to be absorbed. For instance, sucrose is digested into glucose and fructose, and maltose is broken down into two glucose molecules.

Normal digestion

  • Sucrose -->  glucose + fructose

  • Maltose --> glucose + glucose


  • Sucrose -->  sucrose

  • Maltose -->  maltose

Signs & symptoms of CSID

CSID usually becomes apparent in infants after they start to transition from breastmilk/formula to foods/drinks; particularly fruits, juices and grains. In general, a diagnosis is made under the age of 18 months.

Typical symptoms after ingestion of sucrose or maltose:

  • Watery diarrhoea

  • Bloating

  • Excess gas production

  • Abdominal pain (stomach ache)

  • Malabsorption of other nutrients

  • Nausea, vomiting and reflux symptoms (sometimes)

  • Poor weight gain and growth (failure to thrive)

  • Malnutrition

Prevalence (how common is CSID)

  • Estimates for those of European descent: between 1 in 500 to 1 in 2000 people

  • Indigenous populations of Greenland, Alaska and Canada: between 1 in 10 to 1 in 30 people

  • Other areas: unknown (limited information)


CSID is caused by mutations in a gene known as the sucrose-isomaltase gene. The sucrose-isomaltase gene contains instructions for producing the enzyme sucrase-isomaltase. This is a digestive enzyme that is found in your small intestine and is involved in the digestion of sugar and starch. It is responsible for breaking down sucrose and maltose.

Your gut motility, diet, nutritional interactions and other genetic variations can also affect the severity of symptoms in CSID.


  • CSID is diagnosed via an endoscopic biopsy; a tissue sample taken from your small intestine.

  • A sucrose breath hydrogen test can also be used, however it is susceptible to error.

  • A carbon-13 breath test is a more recently developed test that is non-invasive and has a high degree of accuracy.

  • Genetic testing can also be used.

Treatment/management includes:

  • A strict sucrose-free diet, that is personalised to tolerance levels.

  • Individualised nutrient requirement recommendations to ensure proper nutrition and growth.

  • Modified starch intake. This may include restrictions on cereals, breads, pastas and potatoes (those high in a starch component known as amylopectin).

  • Starch tolerance is generally improved after the age of 3-4 years.

  • Rice and maize starch are often easier to digest.

  • Taking a small amount of baker’s yeast along with sucrose-containing foods has been found to reduce symptoms.


  • Most children are better able to tolerate sucrose and maltose as they get older.

  • Symptoms can sometimes be mistaken for IBS-D or dyspepsia.

  • Some people do not get common symptoms and can remain undiagnosed.

  • Sacrosidase (sucraid) is an enzyme replacement therapy that assists sucrose digestion. It is available by prescription.

  • It is essential to seek guidance from your Dietitian and Gastroenterologist for managing this condition.


  1. US National Library of Medicine. Congenital sucrase- isomaltase deficiency. Genetics Home Reference. July 2008; isomaltase-deficiency. Accessed 10/08.2014.

  2. NASPGHAN and NASPGHAN Foundation for Children’s Digestive Health and Nutrition. Recognition and management of dietary carbohydrate-induced diarrhea in pediatric patients. October 2011; resources/nutrition/Disaccharide Newsletter_11-17-11.pdf. Accessed 10/08/2014.

  3. Puntis JWL, Zamvar V. Congenital sucrose-isomaltase deficiency: diagnostic challenges and response to enzyme replacement therapy. Arch Dis Child 2015;100:869-871

  4. Treem WR. Clinical aspects and treatment of congenital sucrose-isomaltase deficiency. J Pediatr Gastroenterol Nutr. 2012 Nov;55 Suppl 2:S7-13