What Is Sucrose Intolerance?

Discovering CSID

Congenital Sucrase-Isomaltase Deficiency (CSID) is a rare disorder that is equally prevalent in males and females. It may also be referred to as Sucrose Intolerance, sucrase-isomaltase (SI) deficiency, disaccharide intolerance, and Genetic Sucrase-Isomaltase Deficiency (GSID).

CSID is a disorder that causes a reduction in the activity of the enzymes sucrase and isomaltase, which are responsible for the breakdown and absorption of table sugar (sucrose) and other sugars found in dietary starches. The figure below shows the difference between a normal intestine, where digestive enzymes are present, and a CSID intestine that lacks the sucrase-isomaltase enzymes.

CSID Intestine vs. Normal Intestine

What Causes Sucrose Intolerance?

The digestive enzymes sucrase and isomaltase are responsible for the breakdown of certain sugars. These two enzymes are part of the normal digestive process that occurs in the small intestine when consuming sugar-containing foods. When these enzymes are not functioning optimally due to CSID, sugar and starch are digested, but cannot subsequently be absorbed in the small intestine. The sugar and starch end up in the large intestine, resulting in watery diarrhea, pain, gas, and bloating.

A diminished level of sucrase activity can also occur as a result of other disorders, including those that cause irritation or inflammation of the intestinal lining, such as celiac disease or a gastrointestinal infection. In these cases, the level of sucrase activity should return to normal once the primary cause is resolved. However, in patients who have congenital Sucrose Intolerance (CSID), the deficiency is caused by a genetic variation and symptoms will likely persist without diet and/or therapy.

Sucrose (table sugar) is a sugar molecule made in plants by combining two smaller sugars called glucose and fructose. The body cannot absorb sucrose because it is too large to pass into your cells. The sucrase enzyme breaks down sucrose into individual molecules of glucose and fructose, which can then be absorbed. The isomaltase enzyme helps the body break down starches. Both enzymes are produced in the lining of the small intestine. Sucrose and starches must be broken down into their smaller parts so they can be absorbed and used by the body as fuel.

The inability to break down and absorb dietary sucrose and starches may impact the absorption of other nutrients, as well as disrupt normal hormonal regulation of gastrointestinal function. Unabsorbed carbohydrates affect the rate of stomach emptying, accelerate the rate consumed foods move through the small intestine, and contribute to the malabsorption of starches, fats, and monosaccharides.

What Are the Symptoms of Sucrose Intolerance?

Symptoms of Sucrose Intolerance are chronic and frequent, including:

  • watery diarrhea
  • gassiness
  • bloating
  • abdominal pain

Symptoms can vary from mild to severe. Infants, children, and adults can experience symptoms caused by CSID. In addition to the symptoms listed above, individuals affected by Sucrose Intolerance are at risk of chronic malnutrition and, in infants, a failure to thrive.

Sucrose Intolerance Is More Common Than You Think