Dietary intake includes water, carbohydrates, protein, fat, minerals, as well as vitamins, and all these substances need to be effectively absorbed for healthy function. Mechanical and chemical digestion begins in the mouth and continues throughout the digestive tract via acid produced in the stomach and enzymes produced by salivary glands, stomach, intestines, pancreas, and liver.
Structural or functional disruption of this complex series of events can lead to malabsorption, which can vary in it's impact and severity depending on it's cause.
Susan is a 44 year old woman who has experienced slowly worsening symptoms over the past two years. These have included mild abdominal pain, bloating, loose, smelly stools, and 10 lb weight loss. She wonders what could be causing this.
Q: how do you approach Susan’s condition?
There are many causes of malabsorption, which vary with location. There are many infectious diseases common in tropical countries that make the differential diagnosis more difficult.
Parasitic infections include:
Bacterial infections include:
Viral infections include:
As described above, there are many causes of malabsorption. These all act at one or more sites of digestion.
In order to understand the abnormalities of digestive function that result in malabsorption, it is first important to understand that normal GI tract function can be divided into three distinct phases: premucosal (digestive), mucosal (absorptive), and postmucosal (postabsorptive). In the premucosal phase, which occurs in the intestinal lumen, proteins, fats, and carbohydrates are hydrolyzed and solubilized by the action of bile and digestive enzymes. This is followed by the mucosal phase, wherein the digested products are further broken down by brush border enzymes and are taken up from the intestinal lumen into the epithelial cells. Lastly, the nutrients are taken up by the lymphatic system and delivered to the bloodstream for transport throughout the body.These three phases are the major sites at which malabsorption may occur, though technically, interference at the intraluminal phase is more accurately known as maldigestion.
Premucosal disruptions typically occur due to insufficient pancreatic secretory activity and defective bile salt production. Pancreatic enzymes such as lipases break down long-chain triglycerides into fatty acids and monoglycerides; carbohydrates and disaccharides are broken down into their monosaccharide constituents by amylases; and proteins are hydrolyzed into amino acids by trypsins. Thus, as pancreatic secretions and bile salts are essential for digestion, a lack thereof greatly hinders the capacity of the small intestine to break down nutrients.
Disruptions in the absorptive phase tend to occur when there are conditions that affect the integrity of the epithelium and reduce the overall area for absorption of nutrients.
Finally, postabsorptive phase disruptions are related to issues with nutrient transport, such as obstructions in the lymphatic system.
The consequences of malabsorption can be specified to each of major nutrients. Unabsorbed fats trap and interfere with the absorption of fat-soluble vitamins- vitamins A, D, E, and K- and some minerals, leading to nutritive deficiencies. Carbohydrate malabsorption causes the fermentation of the unabsorbed carbohydrates into carbon dioxide and methane, and short-chain fatty acids by colonic bacteria. Gas retention results in abdominal distention and bloating, whilst the accumulation of fatty acids causes diarrhea.
Protein malabsorption can lead to edema, principally due to the role of the protein albumin in maintaining osmotic pressure in the serum. Protein deficiency can also lead to malnutrition, given it’s critical role in tissue synthesis.
Symptoms will depend on the cause, but commonly include the following.
Diarrhea may be extensive, with frequent watery stool, or may not be present. Steatorrhea occurs with impaired fat absorption. Stools are foul-smelling and often float.
Abdominal pain or cramping, bloating, and flatulence may accompany various malabsortive syndromes, especially if undigested carbohydrates pass into the large intestine. This leads to bacterial fermentation and gas production.
Weight loss can occur if intake (and/or absorption) is insufficient. However, patients will sometimes compensate by dramatically increasing intake, thus necessitating an effective dietary history.
Assess the person's diets, especially regarding elimination diets they may have attempted. Encourage the use of a food symptom journal.
Other symptoms caused by prolonged malnutrition include:
Assess the following:
weight, BMI, Waist Circumference
skin folds to help assess muscle mass loss
Ascites and peripheral edema can follow protein loss.
Skin findings can include:
Lab abnormalities can include:
The following imaging tests may be used to investigate potential causes of malabsorption, guided by clinical suspicion.
Barium small bowel follow through: detection of anatomical abnormalities
Endoscopy, with biopsy: analyze specific portions of the GI tract
Endoscopic retrograde cholangiopancreatogram (ECRP): examine bile ducts of liver and pancreatic ducts
Ultrasound and CT scan: evaluation of bowel, pancreas, and other intra-abdominal organs for conditions such as pancreatitis
While assessing malabsorption, it is important to evaluate the possibility of other diseases.
A common cause of chronic diarrhea is irritable bowel syndrome; however, weight loss is not normally seen with this condition
Weight loss should also prompt assessment for occult malignancy, systemic infection such as HIV or TB, or other causes of chronic inflammatory states.
The treatment of malabsorption focuses on two basic principles - treating underlying diseases and correcting nutritional deficiencies.
Malabsorption should prompt cause-specific treatment, especially regarding infections or other conditions that have a therapeutic target. Surgery may also be necessary to remove any obstructions.
Specific examples include:
main article: malnutrition
Supplementation should be offered to replace lost nutrients, including:
In severe cases, intravenous administration of nutrients may be necessary.
Long-term malabsorption may result in the following complications, among others:
Blaauw R. 2011. Malabsorption: Causes, consequences, diagnosis and treatment. S Afr J Clin Nutr. 24(3): 125-127.
Fagundes-Neto U. 2013. Persistent diarrhea: still a serious public health problem in developing countries. Curr Gastroenterol Rep. 2013 Sep;15(9):345.
Juckett G, Trivedi R. 2011. Evaluation of Chronic Diarrhea. Am Fam Physician. 84(10):1119-1126.