Malabsorption is the term for impaired absorption of nutrients from food in the gut. Most absorption occurs within the intestines but the other parts of the gut (gastrointestinal tract) play important roles in digestion which prepares the food for absorption.
Malabsorption often results in deficiencies and the signs and symptoms that may arise are due to this lack of specific nutrients within the body. Other clinical features may not be related to deficiency but are a part of the causative disease or disorder that results in malabsorption.
How does a malabsorption disorder occur?
Pathophysiology of Malabsorption
There are a number of causes of malabsorption and this may be due to disorders affecting the gut itself or other diseases that contribute to impaired nutrient absorption. Malabsorption may occur due to one of the following processes :
Impaired Digestion (Maldigestion)
In this process, the food is not broken down sufficiently to allow for absorption within the small intestines Digestion is a combination of mechanical and chemical processes. Mechanical digestion involves the breaking of the food physically (example : action of teeth, churning in the stomach). Chemical digestion involves the digestive enzymes which are secreted in the mouth, stomach and small intestine.
Any impairment in the structures or compounds for mechanical and/or chemical digestion (digestive enzymes) affect the overall digestive process. The intestinal contents are therefore not sufficiently broken down to be absorbed into the bloodstream.
- Deficiency of pancreatic enzymes or bile may impair hydrolysis and solubilization (chemical digestion).
- Gastric bypass surgery can impair the stomach muscles and affect the churning of food (mechanical digestion).
Impaired Absorption (Malabsorption)
Most nutrients are absorbed in the small intestine. The anatomical characteristics (surface area and permeability) of the small intestine have developed to carry out of the process of absorption. If the surface area or permeability of the epithelium lining the inside of the intestine is affected then nutrients cannot enter the cells and be transported by the bloodstream.
- Surgical removal (resection) of the small intestine decreases the surface area for nutrient absorption.
- Inflammatory bowel disease causes swelling of the intestinal mucosa which reduces the surface area created by the villi and impairs nutrient transport into the bloodstream.
Lymphatic Obstruction (Blockage)
Any blockage affecting the lymphatic drainage will hamper the uptake of lipids (fats) by the lacteals and the subsequent transport of these nutrients. In addition, the lymphatic obstruction results in an increased pressure within the lacteals. This will cause it to “leak” proteins into the intestinal lumen which is known as protein-losing enteropathy secondary to lymphatic obstruction.
Signs and Symptoms of Malabsorption
- Chronic diarrhea (>3 stools per day, >200g/200ml of stool per day persisting for more than 30 days) although normal bowel movements and patterns may be present in some cases.
- The diarrhea is often watery and of a large volume typical of diarrhea due to small bowel disturbances.
- It may be pale with an offensive odor.
- ‘Floaters’ – stools float in the toilet water (steatorrhea).
- Undigested food may be seen in the stools.
- Borborygmi – loud gastrointestinal noises (rumbling, growling).
- Intestinal cramps.
- Abdominal distension.
- Unintentional weight loss – failure to thrive (FTT) in children.
The clinical features of malabsorption (signs and symptoms of deficiencies) may cause additional signs and symptoms that are not mentioned above.
Diarrhea is defined as passing more than 200 grams / 200 milliliters of stool in a day. This occurs within 3 or more bowel movements in a day. The stool is usually loose or watery in consistency. With malabsorption diarrhea, steatorrhea is almost always evident. The stool may appear yellow to pale, greasy and tends to float. Read more on fatty stool.
Excessive flatulence, borborygmi (stomach noises) and abdominal distension usually accompanies the diarrhea and intensifies significantly when consuming foods that cannot be digested or absorbed. Over time there will be loss of appetite, weight loss and muscle wasting. Various symptoms associated with nutrient deficiencies (macro- and micro) will become evident. Read more on vitamin deficiencies.
Diarrhea associated with nutrient malabsorption (malabsorptive diarrhea) is seen with almost all malabsorption syndromes. It is sometimes classified as a type of diarrhea, along with osmotic, secretory and exudative diarrhea, but malabsorption largely contributes to the development of osmotic diarrhea, secretory diarrhea to some extent, and leads to exudative diarrhea. Malabsorption is usually a sub-acute or chronic condition and therefore presents as chronic diarrhea.
The gastrointestinal tract is designed to carry out three main functions :
- Digest food – mechanical and chemical break down of food into simpler compounds
- Absorb nutrients – transport of compounds from the lumen of the gut into the blood stream
- Eliminate wastes – undigested and unabsorbed materials, waste products and water are evacuated through the anus
The process of digestion starts in the mouth but primarily occurs in the stomach and small intestine. Absorption may also start in the mouth and continues throughout the gut although the majority occurs in the small intestine. The lymphatic system is responsible for transporting absorbed fats from the lining of the gut to the blood stream.
How does malabsorption occur?
Malabsorption stems from either defective digestion, defective absorption or lymphatic obstruction. Maldigestion does not allow for foods to be broken down into simpler compounds which can then be absorbed into the blood stream from the gut lumen. With defective absorption, the transport of nutrients across the epithelial lining may be disturbed for various reasons like damage of the epithelium thereby allowing nutrients to remain in the gut. In terms of lymphatic obstruction, the transport of fats is disrupted thereby preventing any fat absorption from the gut.
The presence of these unabsorbed nutrients in the gut affects the osmotic gradient and therefore water absorption from the gut. This leads to osmotic diarrhea as described under runny bowel movements. The unabsorbed nutrients also serve as an additional source of food for intestinal and pathogenic bacteria. This disrupts the normal intestinal flora and can lead to exudative diarrhea.
Types of Malabsorption Disorders
Some of the more common types of disorders that affect digestion, absorption and/or lymphatic drainage.
- Celiac disease
- Tropical sprue
- Infectious gastroenteritis
- Disaccharidase deficienc
- Inflammatory bowel disease
- Lymphatic obstruction
- Whipple disease