Demystifying Carbohydrate Maldigestion: A Clinical Review

Carbohydrate intolerance is a poorly understood and potentially overlooked cause of unexplained gastrointestinal symptoms, particularly among patients with disorders of gut-brain interaction. Symptoms related to carbohydrate intolerance arise from bacterial fermentation of unabsorbed carbohydrates leading to increased gases and osmotic load within the gastrointestinal tract. This mechanism is shared across various carbohydrates, including lactose, sucrose, maltose, fructose, and fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. Primary forms of carbohydrate maldigestion typically affect one specific type of carbohydrate and result from inherited defects in specific brush-border enzymes or transport mechanisms, whereas secondary, or acquired, forms of carbohydrate maldigestion can arise from conditions that affect the structural integrity or function of the pancreas and small intestine. Although confirmation of a disaccharidase deficiency does not imply clinical relevance, obtaining a careful patient history with appropriate use of breath testing, duodenal disaccharidase assay, and response to dietary modification can help identify patients whose symptoms are associated with carbohydrate maldigestion and who may benefit from treatment. Dietary modification remains the cornerstone of therapy for patients with carbohydrate intolerance and should focus on determining the most liberal diet for patients that allows symptom control. Given the complexity and time-consuming nature of this process, clinicians are encouraged to engage the help of dietitians with expertise in the treatment of disorders of gut-brain interaction where available. Enzyme replacement therapy can also be an important adjunct to dietary management, with sacrosidase improving symptoms in sucrase-isomaltase deficiency and helping patients to liberalize their diet.