Glucose-galactose malabsorption (GGM) is a rare metabolic condition. It occurs when a genetic variation makes the body unable to properly absorb the simple sugars glucose and galactose.

Sugars are the primary source of energy for every cell in the body. As such, consuming and using a suitable amount of sugar is necessary for many bodily functions. Typically, most people receive sugars from food their body absorbs.

Monosaccharides are the simplest form of carbohydrates and are often known as simple sugars. Examples of monosaccharides include glucose and galactose. However, people living with GGM are unable to absorb these sugars. This can cause them to experience gastrointestinal problems and other health issues.

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GGM is a genetic metabolic condition where a person is unable to absorb simple sugars, such as glucose and galactose. Glucose is the most abundant simple sugar and the main energy source for the body. Galactose is another simple sugar that is often in dairy products. When glucose and galactose combine, they form the disaccharide lactose.

Read on to learn more about simple and complex carbohydrates.

The condition occurs when the small intestine cannot absorb these simple sugars. This can result in severe diarrhea and dehydration, which can cause severe health complications if a person does not modify their dietary pattern to remove these sugars.

Other names for this condition include:

  • monosaccharide malabsorption
  • carbohydrate intolerance
  • complex carbohydrate intolerance
  • SGLT1 deficiency

GGM occurs due to a genetic variation in the SLC5A1 gene. This gene is responsible for producing a protein known as sodium-glucose cotransporter protein 1 (SGLT1).

GGM is a rare condition, and researchers have only identified a few hundred people with this condition worldwide. However, up to 10% of the population may have a lower capacity for glucose absorption. People typically inherit the gene variation for GGM in an autosomal recessive pattern. This means a person must inherit a copy of the gene alteration from each parent.

The SGLT1 protein is present in the intestinal tract and kidneys. It plays an important role in the functioning of the intestines’ epithelial cells. These are the cells that line the walls of the intestine. The SGLT1 protein helps move glucose and galactose across the cell membrane, so the intestines can absorb these simple sugars.

The alteration in the SLC5A1 gene affects the function of the SGLT1 protein and prevents it from working properly. This means the body cannot absorb these simple sugars in the intestines, which results in an accumulation of glucose and galactose. This also impacts sodium and water absorption, which is why GGM can lead to dehydration and severe diarrhea.

In the kidneys, the SGLT1 protein helps transport glucose into special kidney cells. This helps prevent the body from releasing sugar in urine, allowing it to return to the blood. As such, people with GGM may have sugars present in their urine.

Symptoms of GGM are usually present in the first few days of life after an infant consumes breast milk or infant formula containing lactose. The most common symptoms of GGM in infants include:

Without treatment, these symptoms can become fatal.

In adults, symptoms of GGM may include:

  • bloating
  • nausea
  • diarrhea
  • abdominal cramps
  • rumbling sounds
  • excessive urination

As the SGLT1 protein is also present in the kidneys, people may also experience renal symptoms. These can include mild amounts of sugar in the urine, known as glucosuria, which can be a warning sign that kidney stones are developing.

A doctor may suspect GGM if an infant develops severe diarrhea early in life. There are a few approaches a doctor may use to help them diagnose GGM.

Initially, a medical professional may suggest restricting glucose and galactose to see if this improves symptoms.

Although it is now less common, a doctor may also suggest a hydrogen breath test. This involves drinking a sugary solution and then measuring the amount of hydrogen present in the breath. Higher levels of hydrogen can indicate difficulty breaking down and absorbing sugars in food.

For many people, a medical professional will likely suggest genetic testing to help confirm a diagnosis of GGM. This test will check whether an individual has harmful changes in their SLC5A1 gene.

These tests can also help distinguish GGM from other conditions with similar symptoms, such as:

Treatment and management of GGM will typically involve a specialized diet. This will involve working closely with a dietitian and avoiding glucose, galactose, and foods containing them. Typically, a person can replace these sugars with fructose-based nutrients, as the body absorbs fructose differently than the other sugars.

For infants, a 2019 case study found that an effective treatment may include using glucose and galactose-free milk powders. As they age, a healthcare professional may recommend they follow a high fat, high protein, low carbohydrate diet. This dietary pattern will be rich in fruits and vegetables containing fructose, but low in dairy products and foods containing added sugars.

As the individual ages, they may be able to slowly introduce these sugars. However, a person should only do so with a dietitian’s guidance.

Glucose-galactose malabsorption describes a condition where a person cannot absorb these simple sugars. Due to a genetic alteration, a person does not produce the SGLT1 protein, which helps the intestines absorb these sugars. This can result in symptoms, such as diarrhea and dehydration, which can be severe in infants.

Diagnosis will likely involve excluding these sugars from a person’s diet to see if their symptoms improve. Genetic testing can identify changes in the SLC5A1 gene to confirm a diagnosis. Treatment will involve dietary restrictions on foods containing glucose and galactose.