Gastric Bypass or Roux en-Y

Proximal gastric banding is the most commonly employed gastric bypass technique for weight reduction surgery, and is the most commonly performed bariatric procedure in the United States. It's popularity is due to the fact that it is least likely to result in nutritional difficulties. The small bowel is divided about 45 cm (18 in) below the lower stomach outlet, and is re-arranged into a Y-configuration, to enable outflow of food from the small upper stomach pouch, via a "Roux limb". In the proximal version, the Y-intersection is formed near the upper (proximal) end of the small bowel. The Roux limb is constructed with a length of 80 to 150 cm (30 to 60 inches), preserving most of the small bowel for absorption of nutrients. The patient experiences very rapid onset of a sense of stomach-fullness, followed by a feeling of growing satiety, or "indifference" to food, shortly after the start of a meal.  The "distal" variant of this procedure basically attaches the Y-intersection more distally on the small intestine, almost near the end.  This, as one might guess,  has a higher incidence of nutritional deficiencies.

Graphic of a Gastric Bypass, Roux en-Y