Intestinal malabsorption

Intestinal malabsorption is when the body absorbs nutrients poorly, meaning it has trouble moving them from the intestine into the body. Absorption can go wrong at any point where nutrients are absorbed, and the problem often lies in a stretch of the small intestine, the long tube that follows the stomach.

Absorbing a nutrient is not one step but three, and malabsorption is classified by which of the three fails. It works like a package that has to be opened, brought through the door and delivered around the house, and that can get stuck at any of those steps. The luminal phase happens inside the tube of the intestine: food is mixed and digestive enzymes break it down. The mucosal phase needs the mucosa, the layer that lines the inside of the intestine, to work properly. And the postabsorptive phase needs the blood supply and the lymphatic system, the network of channels through which lymph flows, to be intact.

Three diseases serve as examples. In exocrine pancreatic insufficiency, the pancreas produces too little lipase, a digestive enzyme. In celiac disease, what fails is the mucosa. And in intestinal lymphangiectasia, the flow of lymph fails.