Malabsorption refers to impaired absorption of nutrients . It can result from congenital defects in the membrane transport systems of the small intestinal epithelium (primary malabsorption) or from acquired defects in the epithelial absorptive surface (secondary malabsorption). Another factor that can interfere with nutrient absorption is maldigestion, which is due to impaired digestion of nutrients within the intestinal lumen or at the terminal digestive site of the brush border membrane of mucosal epithelial cells.
Although malabsorption and maldigestion are pathophysiologically different, the processes underlying digestion and absorption are interdependent, so that in clinical practice, the term malabsorption has come to denote derangements in either process.
This topic review will provide an overview of the treatment of malabsorption. Issues that are relevant to specific diseases (eg, pancreatic insufficiency, celiac disease, and short bowel syndrome) are discussed in detail in the appropriate topic reviews. The clinical manifestations, diagnosis, and pathophysiology of malabsorption are discussed separately. (See "Clinical features and diagnosis of malabsorption" and "Mechanisms of nutrient absorption and malabsorption".)
Three steps are required for normal nutrient absorption :
- Luminal events (referred to as the "Luminal" phase)
- Processing at the brush border and absorption into the intestinal mucosa (referred to as the "Absorptive" or "Mucosal" phase)
- Processing within the enterocyte and transport into the circulation (referred to as the "Postabsorptive" or "Processing" phase)