Glucose-galactose malabsorption (GGM) is a rare inherited metabolic disorder that prevents the body from absorbing two simple sugars: glucose and galactose.

Glucose-galactose malabsorption (GGM) is a very rare inherited genetic condition, with only approximately 300 cases worldwide.

GGM is also sometimes known as SGLT1 deficiency. This is because a change to the SGLT1 protein impairs the body’s ability to absorb glucose and galactose.

People with GGM may experience severe, potentially life threatening diarrhea and gastric distress if they consume glucose or galactose.

This article takes a closer look at this rare health condition, including causes, symptoms, diagnosis, and treatment.

GGM is a metabolic disorder that prevents the small intestines from being able to absorb or use the simple sugars glucose and galactose.

Normally, the SCL5A1 gene produces a protein (SGLT1) that causes glucose and galactose to be absorbed into the cells that line the intestines as food is digested. This protein also helps to transport glucose into specialized kidney cells so that it’s not released into the urine.

However, in people with GGM, the SLC5A1 gene is mutated in such a way that it impairs or eliminates the SGLT1 protein’s abilities, and glucose and galactose accumulate in the intestines.

Not only do the glucose and galactose in food fail to be absorbed in those with GGM, but water that would’ve transferred with them is drawn into the intestinal tract. This causes severe osmotic diarrhea, one of the most common symptoms for those with GGM.

What’s the difference between glucose-galactose malabsorption and lactose intolerance?

Similar to GGM, lactose intolerance is a condition where insufficient enzyme is produced in the intestines. This interferes with the intestine’s ability to break down lactose or milk sugar.

People with lactose intolerance may experience digestive issues such as diarrhea, boating, and gas.

Unlike GGM, lactose intolerance is a common condition and potential causes can differ. Lactose intolerance may be related to aging, illness or injury, or a genetic mutation.

Read more about lactose intolerance.

GGM is caused by a harmful mutation to the SCL5A1 gene.

GGM is a recessive genetic condition that requires a person to inherit a mutated SCL5A1 gene from both parents. If they inherit one typically functioning gene and one harmfully mutated gene, they’re considered a carrier and will typically not show symptoms or only mild symptoms.

If two carrier parents have a child, their child will have a 25% chance of having the disease and a 50% chance of being a carrier like their parents. This same risk exists for each pregnancy.

Although the risk of inheriting a modified SCL5A1 gene is the same for males and females, it’s currently more commonly seen in females.

Severe diarrhea is a common symptom of GGM. It should be taken seriously as it can lead to dangerous dehydration. In infants, it can cause difficulty gaining weight and may be deadly.

Other symptoms of GGM can include:

  • bloating
  • nausea
  • abdominal cramps
  • rumbling sounds from extra gas in the intestines
  • frequent urination

GGM can be diagnosed by testing the SLC5A1 gene for harmful changes.

Doctors may also use a glucose hydrogen breath test to determine whether you’re having trouble digesting sugar. This test involves drinking a sugary solution and then breathing into a bag every 15 to 20 minutes as the drink is digested.

A GGM diagnosis may be confirmed by restricting dietary sugars to see whether symptoms stop.

Treatment for GGM involves avoiding foods with glucose or galactose. You’ll also need to refrain from consuming milk or milk products. However, you may be able to consume foods with fructose, another simple sugar, instead.

Infants who are diagnosed with GGM may be fed a special formula without glucose or galactose. As they age, low-carbohydrate vegetables and fruits can be introduced.

Gradually, proteins and a small amount of carbohydrates may be added, but a specialized carbohydrate-free plus fructose formula is still typically used to meet the majority of their nutritional needs.

For adults with GGM, your doctors may recommend a diet high in fat and protein but low in carbohydrates. A GGM diet will include plenty of fruits and vegetables, but dairy and added sugar will be limited.

Foods to eat on a GGM diet

Some foods that may be approved for a GGM diet include:

  • special formula without glucose or galactose
  • honey
  • fruits and vegetables
  • meat
  • fish
  • eggs
  • legumes

Foods to avoid on a GGM diet

On the other hand, foods to avoid on a GGM diet may include:

  • cheese
  • yogurt
  • butter
  • corn syrup
  • ice cream
  • candy
  • chocolate

The severe diarrhea associated with GGM can be fatal, especially in infants, so it’s important to diagnose and begin treatment for GGM as soon as possible.

Some people with GGM are able to slowly introduce glucose and galactose into their diet, but others may need to refrain from consuming glucose and galactose for the rest of their lives.

Your doctor and nutritional team can recommend an appropriate dietary plan to test gradual reintroduction.

GGM prevents your body from properly absorbing glucose and galactose. It’s caused by a rare inherited genetic change to the SLC5A1 gene.

One of the most common signs of GGM is severe diarrhea after consuming glucose or galactose.

Your doctor can use genetic testing to confirm GGM. Some people with GGM are able to slowly reintroduce glucose and galactose back into their diet, but you may have to avoid foods with these simple sugars for the rest of your life.