Sugar intolerance is a digestive condition where the body cannot properly break down and absorb certain carbohydrates, specifically sugars, leading to uncomfortable gastrointestinal symptoms. These sugars (typically disaccharides or monosaccharides) require specific enzymes or transport proteins within the small intestine for absorption. When these mechanisms are insufficient, the sugar passes undigested into the large intestine. There, resident gut bacteria ferment the unabsorbed sugar, producing gases and byproducts that cause physical discomfort. This inability to process specific carbohydrates is common.
Intolerance Versus Allergy
A sugar intolerance and a sugar allergy involve entirely separate systems in the body. Intolerance is a non-immune response based on the digestive system’s inability to process a substance. The reaction is dose-dependent, meaning a small amount of the problematic sugar may be tolerated without symptoms.
A sugar allergy, however, is an immune system response where the body mistakenly identifies a sugar or associated protein as a threat. This triggers the release of Immunoglobulin E (IgE) antibodies and other chemicals, which can cause severe, immediate, and potentially life-threatening reactions like anaphylaxis. True sugar allergies are extremely rare, and the vast majority of adverse reactions to sugar are due to an intolerance.
Common Types and Underlying Causes
Sugar intolerance is most often caused by a deficiency in the specific enzymes required to cleave disaccharides into absorbable monosaccharides. The most recognized type is lactose intolerance, the inability to digest lactose found in milk and dairy products. This condition results from reduced or absent production of the enzyme lactase in the small intestine.
Another common issue is fructose malabsorption, where the body struggles to absorb the simple sugar fructose, found in fruits, honey, and high-fructose corn syrup. This malabsorption is caused by a deficiency or dysfunction in the transport proteins responsible for moving fructose across the intestinal lining.
A less common condition is sucrose intolerance, which affects the digestion of sucrose (table sugar) and maltose (grain sugar). This is caused by a deficiency in the sucrase-isomaltase enzyme, which breaks down sucrose into glucose and fructose, and maltose into two glucose molecules. When these sugars reach the large intestine intact, the resident bacteria rapidly ferment them, causing discomfort.
Recognizable Symptoms and Diagnosis Methods
The physical manifestations of sugar intolerance are primarily gastrointestinal. Common signs include abdominal pain, bloating, flatulence, and changes in bowel habits, most notably diarrhea. These symptoms typically appear 30 minutes to a few hours after consuming the offending sugar.
Diagnosis often begins with a detailed food diary and an elimination diet to establish a link between the sugar and the symptoms. The most common medical confirmation method is the hydrogen breath test (HBT), which is non-invasive and highly effective for diagnosing lactose and fructose intolerance.
During this test, a patient ingests a measured amount of the suspected sugar, and the hydrogen gas levels in their breath are measured at intervals over several hours. An elevated level of hydrogen indicates that the sugar was not properly absorbed in the small intestine and was fermented by bacteria in the colon. For sucrose intolerance, a similar test using a specialized sucrose solution or an intestinal biopsy to measure the sucrase-isomaltase enzyme activity can be performed.
Managing the Condition Through Dietary Changes
Managing sugar intolerance involves dietary adjustments and the use of enzyme replacement supplements. The most direct approach is the restriction or complete avoidance of the specific sugar causing the reaction. For example, individuals with lactose intolerance may switch to lactose-free dairy products or utilize plant-based milk alternatives.
For those with fructose or sucrose intolerance, management involves carefully reading food labels and limiting high-sugar fruits, processed foods, and table sugar. Enzyme supplements can also be used to aid digestion, providing the necessary enzymes the body lacks. A common example is taking a lactase enzyme pill immediately before consuming dairy products. Similarly, prescription enzyme replacements are available for those with a sucrase deficiency.