Nonalcoholic Fatty Liver Disease and Bariatric Surgery

Sindu Stephen; Ancha Baranova; Zobair M Younossi

Disclosures

Expert Rev Gastroenterol Hepatol. 2012;6(2):163-171. 

In This Article

Bariatric Surgery

According to the guidelines for appropriate clinical selection of patients for bariatric surgery established by the NIH, bariatric surgery can be considered for individuals with a BMI greater than 40 or with a BMI of 35 who have obesity-related comorbidities and have previously attempted weight loss with diet and exercise.[41] Bariatric surgery has been shown to result in sustained weight loss, resulting in an improvement of obesity-related comorbidities, with relative risk of death decreasing by 89% postsurgery.[42] The bariatric surgery-associated reduction in visceral fat has also been shown to improve insulin resistance. Both durable weight loss and improved sensitivity to insulin could potentially contribute to histological improvement of concomitant NAFLD.[43] With an exception of cirrhosis, NAFLD does not increase the risk of postoperative complications among patients undergoing bariatric surgery.[44]

The first bariatric procedure was the jejunocolic bypass, which was followed by the jejunoileal bypass introduced in 1954. These types of surgeries were fraught with complications and were abandoned. In the late 1970s, gastric bypass surgery was further modified to RYGB.[42] An introduction of laparoscopic techniques resulted in shorter hospital stays and a reduction in hospital mortality from 0.89% in 1998 to 0.19% in 2004.[45]

In recent decades, the number of bariatric procedures has steadily risen owing to the obesity epidemic and an increase in obesity-related chronic diseases. Importantly, current systematic reviews have underlined that randomized controlled trials comparing one type of bariatric surgery to another type or a nonsurgical treatment are lacking when it comes to mortality and obesity-related comorbidity end points.[46] According to available data, gastric banding reduces weight to a lower extent than gastric bypass and sleeve gastrectomy (SG); however, it results in shorter operating times and fewer serious complications. As compared with gastric bypass, gastric banding is more often associated with reoperations. SG and gastric bypass reduced weight to a similar extent. Based on findings of 14 observational studies, higher volume centers and surgeons had lower mortality and complication rates.[46]

Bariatric surgery produces weight loss by either malabsorption of nutrients or restriction of calories. Some procedures produce a combination of malabsorption and restriction. The most common surgeries in the USA are RYGB, adjustable gastric banding, biliopancreatic diversion with duodenal switch, and SG (Figure 1).[42] The type of the surgery is influenced by surgical expertise, potential cause of obesity and patient preference.

Figure 1.

Common types of bariatric surgeries.

Restrictive surgical procedures reduce the size of the stomach's reservoir by either bypass or resection, thereby reducing the caloric intake. These procedures produce a more gradual weight loss than malabsorptive procedures.

Vertical banded gastroplasty was predominately used in the 1980s. In this procedure, a stapling device placed four rows of staples in the upper stomach. This was followed by placement of a band on the external gastric surface between the upper gastric pouch and the body of the stomach.[42] In this procedure, caloric intake is limited owing to diminished filling capacity of the gastric pouch for solid food while liquids continue to traverse it. It was mentioned that many patients adapt to liquid preferences by increasing caloric intake from liquid sweets, such as milkshakes or ice cream.[47] Owing to difficulties with maintaining the weight loss and high complication rate, vertical banded gastroplasty has been replaced by laparoscopic-adjustable gastric banding (LAGB).

In LAGB, a band is placed around the upper stomach below the gastroesophageal junction, creating a small gastric pouch. The band is connected to a subcutaneous infusion port, which can adjust the degree of constriction.[48] LAGB-induced weight loss is gradual, the procedure is less invasive and the band can be adjusted postoperatively. In 2011, the FDA approved the use of LAGB in patients with a BMI greater than 30 and obesity-related comorbidities. Currently, LAGB is the most common bariatric procedure performed in the USA.

SG was initially utilized as a bridge procedure in high-risk patients prior to a definitive bariatric surgery. However, many surgeons are now using it as standalone surgery. SG is a laparoscopic partial gastrectomy, whereby the greater curvature of the stomach is resected vertically, creating a long tubular stomach. Owing to removal of the fundus, the resultant stomach structure is resistant to stretching. Moreover, fundic reduction removes most of the ghrelin (satiety hormone)-producing cells, thereby abating hunger.[49] Randomized studies have documented improved weight loss and hunger control at 1 and 3 years after SG compared with LAGB.[50] Studies have also revealed fewer postoperative complications as compared with gastric banding, gastric bypass and duodenal switch operations. Although further studies are needed, SG may be emerging as a preferred bariatric surgery in the future.

Until recently, RYGB remained the most common bariatric procedure performed in the USA. In the past 40 years, this procedure has evolved substantially, and now is primarily performed as laparoscopic surgery. The RYGB procedure divides the upper stomach to create a 20–30-ml capacity gastric pouch, while gastrointestinal continuity is established through a Roux-en-Y small bowel reconstruction. The small intestine is divided distal to the ligament of Treitz and a proximal biliopancreatic limb, 30–60 cm in length, transports pancreatic and biliary secretions to the jejunojejunostomy. The Roux or alimentary limb, 75–150 cm in length, extends from the gastric pouch to the jejunojejunostomy, transmitting ingested nutrients. Major digestion and absorption occurs in the common channel, which extends from the jejunojejunostomy to the ileocecal valve.[51] Numerous studies have revealed sustained weight loss after RYGB.[52]

The biliopancreatic diversion with duodenal switch involves a partial SG with preservation of the pylorus to prevent dumping syndrome. An ileoduodenostoma is created distal to the pylorus. The alimentary and biliopancreatic limbs are usually equal in length, with a short common channel. Biliopancreatic diversion with duodenal switch has been shown to be superior to RYGB in promoting weight loss and resolution of metabolic comorbidities in patients with a BMI >50.[53,54] However, owing to risks of long-term malabsorption, this procedure is not widely used.

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