Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal (GI) tract. Impairment can be of single or multiple nutrients, depending on the abnormality. This may lead to malnutrition and a variety of anemias.
The main purpose of the gastrointestinal tract is to digest and absorb nutrients (fat, carbohydrate, protein, and fiber), micronutrients (vitamins and trace minerals), water, and electrolytes. Digestion involves both mechanical and enzymatic breakdown of food. Mechanical processes include chewing, gastric churning, and the to-and-fro mixing in the small intestine. Enzymatic hydrolysis is initiated by intraluminal processes requiring gastric, pancreatic, and biliary secretions. The final products of digestion are absorbed through the intestinal epithelial cells .
Malabsorption constitutes the pathological interference with the normal physiological sequence of digestion (intraluminal process), absorption (mucosal process), and transport (postmucosal events) of nutrients. Intestinal malabsorption may be due to mucosal damage (enteropathy); congenital or acquired reduction in absorptive surface; defects of specific hydrolysis; defects of ion transport; pancreatic insufficiency; or impaired enterohepatic circulation. Causes of malabsorption include infective agents, structural defects, mucosal abnormality, enzyme deficiencies, digestive failure, or other systemic diseases affecting the GI tract.
Infective agents that may cause malabsorption include: Whipple's disease , intestinal tuberculosis, HIV-related malabsorption, tropical sprue, traveler's diarrhea, and parasites (e.g. Giardia lamblia, fish tapeworm [B12 malabsorption], roundworm, or hookworm). Structural defects (e.g. blind loops, inflammatory bowel disease, among others) also may cause malabsorption. Mucosal abnormalities (e.g. celiac disease , cows' milk intolerance, soy milk intolerance, and fructose malabsorption) may lead to malabsorption. Lactase deficiency, which prevents the breakdown of lactose, is a common cause of malabsorption. In addition, a variety of diseases (e.g. cystic fibrosis, diabetes mellitus, etc. ) are associated with malabsorption.
Diarrhea (watery, diurnal and nocturnal, bulky, frequent stools) is the clinical hallmark of overt malabsorption. These symptoms are due to impaired water, carbohydrate, and electrolyte absorption; or irritation from unabsorbed fatty acids. The latter also results in bloating, flatulence, and abdominal discomfort. Cramping pain usually suggests obstructed intestinal segments (e.g. in Crohn's disease), especially if it persists after defecation. Weight loss can be significant despite increased oral intake of nutrients, as can growth retardation, failure to thrive, and/or delayed puberty in children. Many patients suffer from swelling or edema from loss of protein; anemia (commonly from vitamin B12); folic acid and iron deficiency presenting as fatigue and weakness; and muscle cramps from decreased vitamin D and calcium absorption. Malabsorption may also lead to osteomalacia and osteoporosis, or bleeding tendencies from vitamin K and other coagulation factor deficiencies.
There is no specific diagnostic test for malabsorption. As for most medical conditions, investigation is guided by symptoms and signs. A range of different conditions can produce malabsorption and it is necessary to look for each of these specifically. Microscopic analysis of stool samples, particularly useful with diarrhea, may show protozoa like Giardia, ova of hookworm, cysts, and other infective agents.
Treatment for malabsorption is directed largely towards management of underlying cause. For example, replacement of nutrients, electrolytes, and fluid may be necessary. In severe deficiency, hospital admission may be required for parenteral administration. People whose absorptive surfaces are severely limited from disease or surgery may need long term total parenteral nutrition. Pancreatic enzymes are supplemented orally in insufficiencies. Dietary modification is important in some conditions. For example, patients may be put on a gluten-free diet for celiac disease or taught lactose avoidance for lactose intolerance. Antibiotic therapy will treat small intestine bacterial overgrowth. Cholestyramine or other bile acid sequestrants help reduce diarrhea in bile acid malabsorption.