Surgical intervention has proven to be the most effective method for achieving persistent weight loss and reversing obesity-related metabolic abnormalities. The outcome of surgical treatment for morbid obesity varies according to their weight loss mechanisms.
Although Roux-en-Y gastric bypass (RYGB) is generally considered a mixed, restrictive–malabsorptive procedure, the mechanisms underlying the effects of this operation are incompletely understood. Growing evidence now suggests that diverse physiological changes also contribute to the impact of RYGB on body weight and amelioration of obesity-related comorbidities.1,2
Elucidating the actual mechanism of action of RYGB has become a priority because such knowledge may help devise new surgical procedures as well as identify targets for novel antiobesity and antidiabetic medications. This chapter reviews available data and the hypothesized mechanisms mediating the effects of RYGB.
There are several variations in the technique for the RYGB operation (antegastric, antecolic Roux-limb vs retrogastric, retrocolic; one layer vs two layers anastomosis; stapled vs hand-sewn-please see section IV); however, the commonly performed steps involve the creation of a 15–30 mL divided gastric pouch, a jejunojejunostomy with a 75–150 cm Roux limb, and an end-to-side gastrojejunostomy. The RYGB reduces gastric capacity by 90%–95%. The biliopancreatic limb includes the excluded stomach, duodenum, and proximal jejunum and drains bile, digestive enzymes, and gastric secretions. The mid-jejunum is anastomosed to the gastric pouch (Roux or alimentary limb) and carries ingested food. Food and digestive enzymes mix at the level of the jejunojejunostomy, and absorption takes place in this common channel that may vary in length depending on the patient's BMI.3,4 Our current technique includes four main steps: (1) division of the jejunum 30–50 cm from the ligament of Treitz and measurement of a 75- or 150-cm (for patient with BMI > 50) Roux limb, (2) side-to-side stapled jejunojejunostomy between the Roux and biliopancreatic limb with closure of the mesenteric defect, (3) creation of a 15-mL divided gastric pouch, and (4) creation of a linear stapled end-to-side gastrojejunostomy with hand-sewn closure of the common opening over an endoscope.
The 75–100 cm Roux limb constitutes a short bypass; therefore the technique most commonly used for RYBG is not primarily a malabsorptive procedure. In an attempt to provide a more powerful malabsorptive element to the operation, the long limb or “distal gastric bypass” has been developed. The “distal” RYGB usually consists of an extended Roux limb (150–200 cm) and a 75–150-cm common channel.5,6 Studies have shown that increasing the Roux limb in RYGB effectively increases the excess weight loss in super obese patients (BMI > 50 kg/m2).5,7–9 This increase in weight loss is attributed to the lengthened bypass of the foregut and induction of a state of increase malabsorption. However, a randomized prospective trial demonstrated that lengthening of the Roux limb did not increase weight loss for patients with a BMI lower than 50 kg/m2.10