Definition

Short bowel syndrome (SBS) is a digestive tract disorder characterized by severe malabsorption occurring after a significant resection of the small intestine. The small intestine is considered short when it measures less than 200 cm. Since the majority of nutrients (carbohydrates, fats, and proteins) are absorbed in the first 150 cm of the intestine, this explains the malabsorption associated with SBS. This malabsorption manifests as diarrhea and/or steatorrhea and can lead to malnutrition and metabolic changes that may be fatal. Finally, SBS generally requires the use of parenteral and/or enteral nutrition, as after surgery, the intestine often can no longer maintain adequate levels of various nutrients and hydration.

Etiology

The causes of SBS in adults can be numerous. Among these are surgical resection of a significant section of the small intestine, Crohn's disease, cancer, mesenteric ischemia (interruption of blood flow to the intestine), volvulus (twisting of the intestine on itself), and radiation enteritis (inflammation of the intestine caused by radiotherapy).

Symptoms

The main symptoms of SBS are diarrhea and nutritional deficiencies caused by malabsorption. However, SBS symptoms depend on the anatomy and function of the remaining small intestine.

Resection (surgical removal) of the small intestine and malabsorption

The small intestine is a section of the digestive tract comprising the duodenum, jejunum, and ileum. Depending on which part of the small intestine has been removed, the effects on absorption vary.

With jejunal resection, the number of disaccharidases, enzymes responsible for digesting disaccharides (certain sugars chemically composed of two types of sugars), decreases. The reduction of these enzymes leads to decreased breakdown of disaccharides, a type of carbohydrate that includes lactose. Since undigested disaccharides are not absorbed, this can cause lactose malabsorption and diarrhea.

With ileal resection, the movement of intestinal contents is accelerated and the absorption of vitamin B₁₂ and bile salts is reduced. Malabsorption of bile salts, which are involved in fat digestion, leads to decreased absorption of fats and fat-soluble vitamins (A, D, E, and K). Moreover, unabsorbed fats and bile salts increase in the large intestine and can be altered by intestinal bacteria. Alteration of bile salts can lead to fat malabsorption and may cause steatorrhea. Finally, removal of the ileum also results in decreased absorption of water and electrolytes by the large intestine, which can cause diarrhea and steatorrhea.

Intestinal adaptation

The intestines of people with SBS generally undergo adaptation following surgical resection. The degree of intestinal adaptation depends on various factors including the length of the intestinal resection, the section of the intestine removed, the condition of the remaining small intestine, intestinal continuity, underlying disease, malnutrition, and the patient's age. Usually, intestinal adaptation occurs when the ileum and large intestine are present, but there is little or no adaptation at the jejunum level. Intestinal adaptation includes various changes such as an increase in the number of intestinal cells, enlargement of the ileal villi, lengthening of the intestine, changes in motility, and hormonal changes. All these modifications increase nutrient absorption and thus limit malabsorption. Intestinal adaptation generally spans more than a year and is promoted by factors such as enteral nutrition.

The case of oxalates

Oxalates are compounds naturally present in certain foods and are normally eliminated by the body. However, when the ileum has been removed, oxalates are no longer eliminated and are absorbed by the large intestine. This increases the presence of these compounds in the urine and promotes urinary stones. Oxalates are found in foods such as beets, spinach, nuts, tea, chocolate, strawberries, rhubarb, and wheat bran. People who have undergone ileal resection generally need to follow a diet restricted in oxalates, ensure adequate hydration, and take calcium supplements, which bind to oxalates and allow their elimination.

Nutritional approach

The nutritional approach for SBS in adults consists of preventing water and electrolyte losses and initiating parenteral nutrition providing all necessary macronutrients and micronutrients (carbohydrates, fats, proteins, vitamins, and minerals). Indeed, immediately after surgery, diarrhea is often very severe and patients must receive their nutrition intravenously (parenteral nutrition) to replace losses. Then, fluids are gradually reintroduced orally as the patient stabilizes and stool volume decreases. Finally, people whose intestinal resection has left less than 100 cm of jejunum, as well as those who continue to have excessive losses of nutrients, water, and electrolytes, often require lifelong parenteral nutrition. For those with more than 100 cm of remaining jejunum, oral feeding may be resumed.

Nutritional recommendations

Nutritional recommendations for adults with SBS who can resume oral feeding include:

• Consume small, frequent meals. This helps reduce the risk of diarrhea.
• Drink fluids between meals.
• Have higher protein intake, which is generally well absorbed, and lower simple sugars, which promote diarrhea.
• Follow a low-oxalate diet when the ileum has been removed.
• Take multivitamins according to nutritional needs (e.g., magnesium, calcium, iron, vitamin B₁₂, etc.).

Short bowel syndrome is a digestive tract disorder that can have a significant impact on affected individuals. Moreover, these individuals can have very different profiles depending on the anatomy of the remaining small intestine and intestinal adaptation, which varies from person to person. Consequently, each individual has different needs, and management of short bowel syndrome by healthcare professionals is essential.

References 

1. Bouthillier, Lise. January 2019. "Digestive Tract Diseases." NUT 2047 – Clinical Nutrition 2. Montreal: University of Montreal.
2. D’Aoust, Louise. January 2019. "Short Bowel." NUT 2047 – Clinical Nutrition 2. Montreal: University of Montreal.
3. https://www.merckmanuals.com/en-ca/professional/gastrointestinal-disorders/malabsorption-syndromes/short-bowel-syndrome
4. https://www.merckmanuals.com/en-ca/home/digestive-disorders/malabsorption/short-bowel-syndrome

Article written by:

Marie-Noël Marsan, written in 2021.