Is There Maltose Intolerance? Understanding CSID and Carbohydrate Malabsorption

December 8, 2025 •

4 min read

Maltose intolerance is not a stand-alone condition but is connected to the rare genetic disorder congenital sucrase-isomaltase deficiency (CSID), affecting a person’s ability to break down certain sugars and starches. Because the body has multiple enzymes that can break down maltose, a complete, isolated intolerance is extremely uncommon.

Quick Summary

Pure maltose intolerance is exceedingly rare; the condition is typically a feature of congenital sucrase-isomaltase deficiency (CSID), a genetic disorder impacting the digestion of sucrose and some starches along with maltose. The inability to properly break down these sugars leads to gastrointestinal symptoms that can be managed through diet.

Key Points

Maltose Intolerance is Rare: Isolated intolerance to maltose is extremely rare because multiple enzymes exist to digest it, making a total deficiency unlikely.
CSID is the Main Culprit: Most cases of maltose malabsorption are a symptom of the genetic disorder Congenital Sucrase-Isomaltase Deficiency (CSID), which also affects sucrose and starch digestion.
Enzyme Deficiency Causes Symptoms: The lack of a functional sucrase-isomaltase enzyme leads to fermentation of undigested sugars by gut bacteria, causing gas, bloating, and diarrhea.
Diagnosis Requires Specific Tests: Breath tests and endoscopic biopsy are key diagnostic tools, with a biopsy providing the definitive 'gold standard' confirmation.
Management Involves Diet: The primary treatment is to manage dietary intake of maltose, sucrose, and starch, often with the guidance of a dietitian.
Enzyme Therapy for Sucrose Only: While sacrosidase is available as an enzyme replacement for sucrose, it does not address the maltose or starch components of CSID.
Symptoms Can Mimic Other Conditions: Because symptoms overlap with conditions like IBS, a specific diagnosis is critical to avoid misattribution.

Understanding Maltose and the Digestive Process

Maltose, a disaccharide made of two glucose units, is a type of sugar found in grains, malted products, and some fruits. In a healthy digestive system, enzymes on the brush border of the small intestine, including sucrase-isomaltase and maltase-glucoamylase, break down maltose into glucose, which is then absorbed by the body. This process provides a quick source of energy. However, when these enzymes are deficient, maltose is not properly digested, leading to a condition known as carbohydrate malabsorption.

The Real Connection: Congenital Sucrase-Isomaltase Deficiency (CSID)

Most cases of reported maltose intolerance are actually symptoms of Congenital Sucrase-Isomaltase Deficiency (CSID). This is a genetic disorder where the sucrase-isomaltase enzyme, crucial for digesting both sucrose and some starches, is either missing or has low activity. While the deficiency primarily targets sucrose, the enzyme also has overlapping activity with maltase, causing reduced maltose digestion. The key reason that complete maltose intolerance is so rare is that humans possess at least four different maltase enzymes, so a defect in just one (sucrase-isomaltase) is typically not enough to completely halt maltose breakdown.

Causes and Inheritance

CSID is inherited in an autosomal recessive pattern, meaning an individual must inherit a mutated gene from both parents to develop the condition. The severity of the enzyme deficiency can vary widely among individuals based on the specific genetic mutations. This genetic basis means the condition is present from birth, though symptoms may only appear once solid foods containing sucrose or starch are introduced to an infant's diet.

Symptoms of Maltose and Carbohydrate Malabsorption

When malabsorption occurs, the undigested carbohydrates travel to the large intestine, where they are fermented by gut bacteria. This fermentation process produces gas and other byproducts, causing a range of uncomfortable gastrointestinal symptoms.

Abdominal pain and cramping
Excessive gas and bloating
Watery diarrhea
Nausea and, in some cases, vomiting
Poor weight gain or failure to thrive in infants and children
Chronic diarrhea that may lead to malnutrition

Diagnosing Maltose and Carbohydrate Intolerance

Because the symptoms of carbohydrate malabsorption, including those from maltose, can overlap with other digestive conditions like Irritable Bowel Syndrome (IBS), diagnosis requires careful medical assessment.

Diagnostic Procedures

Hydrogen Breath Test: A non-invasive test where the patient consumes a specific sugar solution (e.g., sucrose or maltose). If the sugar is malabsorbed, gut bacteria ferment it and produce hydrogen gas, which is measured in the patient's breath. A significant rise in hydrogen levels indicates malabsorption.
Endoscopic Biopsy: Considered the "gold standard" for diagnosis, this invasive procedure involves taking a tissue sample from the small intestine during an endoscopy. A disaccharidase assay is performed on the tissue to measure the actual activity levels of enzymes like sucrase-isomaltase and maltase.
Genetic Testing: Genetic analysis can identify specific mutations in the SI gene that cause CSID.
Dietary Challenge/Elimination: After a period of elimination, reintroducing the suspected carbohydrate can help identify the trigger for symptoms.

Management and Treatment

There is no cure for CSID, but the symptoms caused by maltose and sucrose malabsorption can be effectively managed through a combination of dietary modifications and, in some cases, enzyme replacement therapy.

Dietary Adjustments

Reduce Maltose and Sucrose: Limiting or avoiding foods high in maltose and sucrose is the primary approach. Foods to be cautious with include:
- Grains and cereals (especially processed ones)
- Beer and malted beverages
- Processed baked goods like bread, bagels, and cookies
- Some candies and sweet products
- Syrups, including corn and maple syrup
Adjust Starch Intake: Since some starches may also be poorly digested, limiting intake of potatoes, rice, and pasta may be necessary, depending on individual tolerance.
Consult a Dietitian: Working with a registered dietitian is crucial to ensure adequate nutrition is maintained while restricting certain carbohydrates.

Enzyme Replacement Therapy

Sacrosidase (Sucraid®) is an oral enzyme replacement therapy that can help with sucrose digestion. However, it does not aid in the digestion of maltose or starch. Therefore, dietary modifications for maltose and starch may still be required.

Comparison: Allergy vs. Intolerance vs. CSID


Feature	Food Allergy	Food Intolerance	Maltose Intolerance (CSID)
Mechanism	Immune system reaction to a food protein.	Inability to digest or process a food component; not immune-mediated.	Inadequate digestive enzymes (sucrase-isomaltase) due to a genetic defect.
Symptoms	Can affect multiple systems; can be life-threatening (anaphylaxis).	Primarily gastrointestinal, uncomfortable but not life-threatening.	Primarily gastrointestinal (bloating, diarrhea, gas), can cause poor growth in children.
Severity	Can be severe and rapid-onset, even with tiny amounts.	Dependent on the amount of food consumed; reactions are generally less severe.	Dependent on the amount of maltose/sucrose/starch consumed and individual enzyme levels.
Diagnosis	Skin prick tests, blood tests for IgE antibodies, oral food challenges.	Symptom history, elimination diets, hydrogen breath tests.	Endoscopic biopsy (gold standard), hydrogen breath tests, genetic testing.
Management	Strict avoidance of the allergen; emergency medication like epinephrine.	Limiting or avoiding the problematic food; small amounts may be tolerated.	Dietary restrictions of sucrose and maltose; sacrosidase enzyme therapy for sucrose.

Conclusion: Navigating a Diagnosis

While a true, isolated maltose intolerance is not recognized as a separate clinical entity due to the presence of multiple maltase enzymes, the malabsorption of maltose is a key feature of Congenital Sucrase-Isomaltase Deficiency (CSID). This rare but impactful genetic condition impairs the digestion of not only maltose but also sucrose and certain starches, leading to classic gastrointestinal symptoms. Accurate diagnosis through breath tests, endoscopic biopsy, and genetic analysis is essential for effective management. With proper dietary adjustments and, for sucrose, potential enzyme replacement therapy, individuals with CSID can effectively control their symptoms and lead healthy lives. For further information on living with CSID, consult resources such as the International Foundation for Functional Gastrointestinal Disorders (IFFGD).

Frequently Asked Questions

Maltose intolerance is not a distinct medical condition. The inability to properly digest maltose is typically a symptom of the genetic disorder Congenital Sucrase-Isomaltase Deficiency (CSID), which affects the digestion of multiple carbohydrates, including sucrose and some starches.

Maltose is found in malted products like beer and malted beverages, as well as starches. It is present in foods like processed baked goods, grains, certain cereals, corn syrup, and some candies.

The condition is diagnosed via tests for carbohydrate malabsorption, such as a hydrogen breath test, which measures gas produced by gut bacteria fermenting undigested sugar. A small intestinal biopsy is the most definitive method, directly measuring enzyme activity.

Symptoms include watery diarrhea, abdominal cramps, bloating, excessive gas, and nausea. In infants, it can manifest as poor weight gain and failure to thrive.

No, there is currently no cure for the underlying genetic defect causing CSID. However, symptoms can be managed effectively through dietary restrictions and, for sucrose, enzyme replacement therapy.

Tolerance varies greatly among individuals with CSID. Some may tolerate small amounts of maltose and starch, while others need strict restrictions. A personalized diet plan guided by a dietitian is recommended.

A food allergy is an immune system reaction, which can be life-threatening (anaphylaxis). CSID is a digestive enzyme deficiency that causes gastrointestinal distress but is not an allergic reaction and does not involve the immune system.