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Bariatric Surgery

Gastric Bypass

How is a gastric bypass done?


To do a gastric bypass, the surgeon uses surgical staples to make a small pouch in the upper part of the stomach. The pouch is about the size of an egg or golf ball, and holds 30 to 50 mL (2 to 3 tablespoons) of food or fluid.

The surgeon will then use more staples to separate the upper part of the small intestine from the middle part of the small intestine. The middle part of the small intestine is then attached to the gastric pouch. This directs food into the middle part of the small intestine, instead of the lower part of the stomach.

The upper part of the small intestine is then reattached to the middle part of the small intestine, so digestive juices from the stomach, pancreas, and gallbladder can mix with the food to help with digestion.​

How does a gastric bypass help you lose weight?

The stomach pouch is small so you’ll only be able to eat a small amount of food at a time. The pouch holds about a ½ cup to 1 cup (125 to 250 mL) of food. This will make you feel full much sooner than you did when your stomach was full size. The smaller opening in the gastric pouch also slows down the movement of food and drinks out of the pouch which may help you feel full longer.

When you eat less food, you may take in fewer calories. Taking in fewer calories will help you lose weight. You may gain weight back if you take in extra calories by:

  • often choosing higher calorie foods
  • eating too much or eating small amounts of food too often (called grazing)
  • often choosing very soft or liquid food and drinks that go through the gastric pouch easily

What are the risks or side effects of a gastric bypass?

The following are some of the risks and side effects of having a gastric bypass.

Feeling too full or sick after eating

If you eat more than the pouch can hold, you will feel uncomfortable. You may feel sick to your stomach and throw up.

Dumping syndrome

If you have food and drinks that are higher in sugar, you may develop dumping syndrome. This is a group of symptoms that happen when food moves too fast from the stomach to the small intestine. Symptoms include nausea, vomiting, diarrhea, stomach pain or cramping, weakness, dizziness, flushing, sweating, anxiety, and a fast heart rate.

Not getting enough vitamins and minerals

Your body will absorb fewer nutrients from the food you eat because food doesn’t go into the lower part of the stomach and the upper part of the intestine. You are at risk for low levels of many vitamins and minerals because you are eating less and your body can’t absorb as many nutrients. To help your body get enough vitamins and minerals after surgery:

  • eat healthy meals and snacks
  • take vitamin and mineral supplements each day

You should also go for regular blood tests to check your vitamin and mineral levels. This will help your healthcare team know how many extra vitamins and minerals ​your body needs.​​​​​

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