Glucose & galactose intolerance

Glucose and galactose malabsorption / intolerance

Glucose & galactose intolerance


Glucose and galactose are two common sugars, which are present in many foods. They are found as free sugars, but also in combination with other sugars (e.g. sucrose – table sugar – is made up of glucose and fructose, lactose – milk sugar – is made up of glucose and galactose, maltose is made up of molecules of glucose).

The malabsorption and intolerance of glucose and galactose is due to an abnormality in the SLC5A1 gene on chromosome 22 regulating a sugar transporter protein (SGLT1), leading to a decreased ability to absorb the sugars across the lining (mucosa) of the small intestine and resulting in symptoms when these sugars are eaten.

The failure to absorb the sugars from the intestine leads to massive attraction of water into the intestines and a reversible change in gut function.

Frequency in population and natural history

Glucose-galactose malabsorption is rare, with only a few hundred cases identified worldwide, with an increased risk in cases of familial intermarriage. Up to 10% of the population may have a slightly reduced capacity for glucose absorption without significant associated health problems. This condition may be a milder variation of glucose-galactose malabsorption. Both parents of the affected individual will be carriers of the genetic defect, but generally without symptoms (autosomal recessive condition).

Symptoms begin at first exposure of infants to these sugars and avoidance will lead to subsidence of symptoms. The intolerance may become less severe or even disappear in older children.

Malabsorption and intolerance of galacto-oligosaccharides is a distinct condition and belongs to the so-called FODMAP intolerance spectrum common in functional bowel syndromes, such as Irritable Bowel Syndrome.


Glucose-galactose malabsorption commonly becomes apparent in the first weeks of a baby’s life.

Typical symptoms are severe diarrhea leading to life-threatening dehydration, destabilization of the acidity of the blood and tissues (acidosis), stomach cramps, bloating, excess gas production, vomiting, and weight loss when fed breast milk or regular infant formulas. They can, however, digest fructose-based formulas that do not contain glucose or galactose. As they get older, affected children or adults often tolerate glucose and galactose better. Glucose in the urine (glucosuria) can be observed. Kidney stones or calcium deposits in the kidneys are more frequent, as the genetic disorder can also affect the kidneys.

Testing and diagnosis

Genetic analysis is the most accurate test. Glucose breath testing can also be performed.

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Avoid ingestion of glucose and galactose, as well as sugars containing them (e.g. lactose, sucrose). This means avoiding table and milk sugar in all forms, such as sugar cane and sugar beets, sorghum, confectioners’ sugar or powdered sugar, rock candy, brown sugar (made of white sugar and molasses), cotton candy, maple syrup, Demerara and Barbados sugar, molasses, pancake syrup, gingerbreads, baked beans and pumpernickel breads, as well as dairy products. Expert dietary advice is required to implement this complicated dietary regime.

Foods that contain Glucose Foods that contain Galactose