Surgical techniques can grossly be categorized by their underlying mechanisms. The two main mechanisms resulting in weight loss are restriction and malabsorption.
Restriction means that the possible food intake is limited due to surgical alterations of the anatomy. This can be achieved by diminishing the volume of the stomach. Typically this mechanism is found in the Gastric Banding or when implanting other devices (Gastric balloon, Bari-Clip etc). Malabsorption means that not all nutrients can be absorbed. Our nutrition consists from macronutrients (proteins, carbohydrates, fat) and micronutrients (vitamins, minerals). Malabsorptive procedures reduce the body's capability of absorbing nutrients by shortening the length of the small bowel that participates in the process of absorption. In recent years more mechanisms have been discovered. Especially changes in the microbiome and in the humoral response to food intake seem to be very important factors, especially regarding the remission of obesity related comorbidities. It has been shown, that the microbiome changes its composition after surgery, resulting in a normal composition, identical to healthy peers within the first months. The restitution of a normal humoral response is occurring even faster after surgery. These changes can be measured a few hours after the intervention. The humoral effects of bariatric surgery might be the most important factor leading to resolution of comorbidities after surgery. Especially the impressive remission rates of Type 2 Diabetes seems to be linked to these effects. These very important mechanisms however are not found in all bariatric procedures! Purely restrictive procedures have a very limited long term success rate. The intra gastric balloon can only achieve a temporary weight loss while in place. Immediate rebound effects are observed after removal of the device. The Gastric Band shows better results in term of long term weight loss (approximately 30% excessive BMI loss). There are many potential problems associated with the Gastric Band, especially esophageal dismotility, band migration or band slippage. Due to the overall unfavorable results, the Gastric Band has been mainly abandoned.The Roux-en-Y Gastric Bypass represents the golden standard in bariatric surgery. It has been described first in the 1960s and has since gained popularity worldwide. It combines the mechanisms of restriction (formation of a small gastric pouch) and malabsorption (partial bypassing of small intestine and complete bypassing of the residual stomach) without putting the patient at a risk for severe malabsorption. Furthermore the humoral effects are very strong in this procedure. Overall the Roux-en-Y Gastric bypass results in long term weight loss (approximately 70% excessive BMI loss) and resolution of comorbidities. The Sleeve Gastrectomy is the second well established standard bariatric procedure today. In this procedure the largest part of the stomach is resected, resulting in restriction. Due to the partial resection of the stomach, effects on the humoral system are present as well. These effects are almost identical to these found after Roux-en-Y Gastric Bypass. Accordingly the long term weight loss is comparable to a Roux-en-Y Gastric Bypass (approximately 65-70% excessive BMI loss).The Omega-Loop Bypass is a newly developed procedure that is similar to the Roux-en-Y Gastric Bypass. The main differences are the lack of a second anastomosis and a longer biliopancreatic limb. The longer biliopancreatic limb of this bypass results in a higher grade of malabsorption, but might also benefit an even stronger humoral effect. As this procedure is still under evaluation, it can't be considered a standard procedure yet.The biliopancreatic diversion represents a very distal gastric bypass. By excluding most of the small intestine from absorption it results in severe malabsorption. This procedure shows excellent results in terms of long term weight loss (Excessive BMI loss of approximately 85%) and resolution of comorbidities. However important side effects must be taken into account. Therefore this operation is considered for highly selected patients only. In most cases it is performed as a second line therapy after initial Sleeve Gastrectomy in super-obese patients (BMI above 60).
Gastric banding, gastric balloon: Pure restriction, no malabsorption, no humoral effects
Sleeve Gastrectomy: Restriction, very limited malabsorption, important humoral effects
Roux-en-Y Gastric Bypass: Limited restriction, malabsorption and important humoral effects
Omega-Loop Bypass: Limited restriction, important malabsorption, important humoral effects Biliopancreatic Diversion: Limited restriction, very important malabsorption, very important humoral effects..