Malabsorptive bariatric surgery is a weight-loss procedure for severe obesity. These surgeries reduce weight by limiting the absorption of calories and nutrients within the digestive system. This method physically reroutes a portion of the small intestine, reducing the time and surface area available for food absorption. This surgical intervention is considered for individuals who have not achieved sustainable weight loss through other means.
The Mechanism of Malabsorptive Surgery
Malabsorptive bariatric surgeries modify the gastrointestinal tract to reduce nutrient absorption by bypassing a segment of the small intestine, where most nutrient absorption occurs. When surgeons reroute the small intestine, they shorten the pathway food travels, limiting its exposure to digestive enzymes and absorptive surfaces. This reduction in absorptive surface area decreases the calories, fats, and other macronutrients the body absorbs. Additionally, these procedures can alter the flow of digestive juices, like bile and pancreatic enzymes, diverting them to a more distal part of the small intestine, which further limits the digestion and absorption of nutrients. Unlike purely restrictive surgeries that only reduce stomach size, malabsorptive procedures primarily drive weight loss through altered absorption, often with a restrictive component.
Types of Malabsorptive Procedures
Among malabsorptive procedures, Biliopancreatic Diversion with Duodenal Switch (BPD/DS) is an effective option. It involves two main components. First, a large portion of the stomach is removed, creating a smaller, tube-shaped stomach pouch, similar to a sleeve gastrectomy. This restrictive element limits the amount of food that can be consumed at one time.
The second component involves rerouting the small intestine to induce malabsorption. The duodenum is divided just beyond the stomach’s outlet. The ileum is then connected directly to this newly divided duodenum, bypassing approximately 75% of the small intestine where much nutrient absorption normally takes place. The bypassed segment, carrying bile and pancreatic enzymes, is reconnected further down the intestine, allowing these fluids to mix with food in a shorter “common channel” for final absorption. This extensive bypass significantly reduces calorie and fat absorption.
Historically, the Jejunoileal Bypass (JIB) was an earlier malabsorptive procedure. It involved bypassing most of the small bowel, creating extreme malabsorption. JIB was abandoned by the mid-1980s due to severe complications, including chronic diarrhea, electrolyte imbalances, and liver disease, sometimes leading to liver failure. Complications were linked to bacterial overgrowth in the bypassed “blind loop” of the intestine. The outcomes of JIB highlighted the need for safer malabsorptive approaches, leading to procedures like BPD/DS.
Expected Health and Weight Loss Results
Malabsorptive bariatric procedures lead to significant and sustained weight loss. Patients undergoing procedures like BPD/DS can experience an average excess weight loss of 60-70% or greater at five-year follow-up. This weight reduction impacts various obesity-related health conditions.
The effect on type 2 diabetes is notable, with BPD/DS achieving high remission rates. Type 2 diabetes remission rates can reach 90% at one to two years post-surgery, with 68% of patients in complete remission even at ten years. Improvements are also observed in other comorbidities, including hypertension, high cholesterol, and obstructive sleep apnea, with resolution rates often exceeding 90% within one year of BPD/DS.
Nutritional Deficiencies and Long-Term Care
Malabsorptive bariatric surgery creates a risk for specific nutritional deficiencies, as bypassed small intestine segments are where many nutrients are absorbed. Managing these risks requires lifelong commitment. Patients commonly experience deficiencies in protein, iron, calcium, and fat-soluble vitamins (A, D, E, and K). Other deficiencies include vitamin B12, folate, and thiamine.
Protein deficiency can lead to hair loss or anemia. Iron deficiency is a common cause of anemia. Calcium and vitamin D deficiencies impact bone health, requiring monitoring and supplementation to prevent osteoporosis. Fat-soluble vitamin deficiencies, particularly vitamin A, can occur.
Managing these risks requires a structured, lifelong approach. Patients must adhere to a high-protein diet to counter malabsorption. A lifelong regimen of specialized vitamin and mineral supplements is also required, often in chewable, liquid, or powder forms. Regular, lifelong follow-up with a medical team is also necessary, including routine blood work to monitor nutrient levels.