In gastric bypass (GBP) surgery, most of the stomach is separated away from a small “pouch.” This pouch is about one ounce after surgery (the size of a golf ball). This is where your food will go after you swallow. The amount of food you can eat will be very small. Weight loss mostly occurs because portion sizes are limited. Also, levels of ghrelin (a “hunger” hormone) decrease, so your appetite is initially reduced.

After GBP, connection from your pouch to your intestines will be a fixed opening, similar to a small funnel.  You will have to avoid certain foods, such as simple sugars like honey, white sugar, or syrups because of this.

Along with your stomach, the top part of your intestines will also be bypassed, meaning that food will not pass through that area.  This causes some malabsorption of vitamins and minerals. 

Diagram of Gastric Bypass Surgery (Roux-en-Y Gastric Bypass)

Possible Advantages

  • Reduced hunger
  • Restricted portions
  • High sugar foods may cause dumping syndrome
  • High fat foods may cause steatorrhea (a type of diarrhea)
  • Durable weight loss
  • Improvement or complete resolution of more than 40 weight-related diseases

Possible Disadvantages

  • Ulcers from smoking or NSAID use
  • Stricture or narrowing of opening to intestines
  • Reactive hypoglycemia or low blood sugar between meals
  • Bypassing the intestines may lead to vitamin or mineral deficiency
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