Weight loss surgery

Weight loss surgery is a way of losing weight for people who are obese, committed to losing weight and have failed conventional weight loss approaches. After surgery, a healthy diet and exercise is important for maintaining weight loss.

What is weight loss surgery?

Weight loss surgery, also called bariatric or metabolic surgery, is sometimes used as a treatment for people who are obese. 

The surgery can lead to significant weight loss and can help improve many obesity-related conditions, such as type 2 diabetes or high blood pressure.

However, it's a major operation and generally should only be considered after trying to lose weight through a healthy diet and exercise.

Who can have weight loss surgery?

You may be eligible for the surgery if you meet certain criteria. This includes if:

  • you have a high body mass index (BMI) (over 40) or a BMI over 35 and an obesity-related condition that might improve if you lost weight, eg, type 2 diabetes or high blood pressure
  • you've tried all other weight loss methods, such as dieting and exercise, but have struggled to lose weight or keep it off
  • you agree to long-term follow-up after surgery – such as making healthy lifestyle changes, taking long term multivitamins and attending regular check-ups
  • you do not smoke, or you stopped smoking at least 3–6 months ago.

Your doctor will be able to talk to you about the criteria in more detail. They can also talk to you about whether weight loss surgery is the right option for you. Although the success rate for most weight loss surgery is high, make sure you understand the risks and what to expect before and afterwards.

What are the different types of weight loss operations?

There are several different types of weight loss surgery. These are the 3 most common types in Aotearoa New Zealand:

Sleeve gastrectomy. This surgery removes the outer three-quarters of your stomach so it’s much smaller than it was before. The rest of the stomach is shaped into a long gastric tube or ‘sleeve’. This means you cannot eat as much as you could before surgery and you'll feel full sooner.

Roux-en-Y gastric bypass
. A gastric bypass is where a small pouch is made at the top of your stomach. The pouch is then connected to your small intestine, missing out (bypassing) the rest of the stomach. This means it takes less food to make you feel full and you'll absorb fewer calories from the food you eat.

One anastomosis gastric bypass. This is similar to the Roux-en-Y bypass but requires only 1 not 2 joins of the bowel. This means you eat less and absorb fewer calories.

Image: Canva

What happens after the surgery?

Surgery on its own does not lead to long lasting weight loss. It is only an opportunity/tool for you to change eating habits, increase daily physical activity and commit to lifelong follow up. Read more about some keys to success after surgery.

There can be problems, even a long time after the operation. Problems may be related to:

  • The surgery itself, depending on the procedure, eg, leaking from a staple line/join, stricture, reflux or hernia. Another operation may be needed.
  • Missing vital vitamins and minerals. Supplements may need to be taken for the rest of your life to prevent this. Eating a good diet is also helpful.
  • The major change you’ve had. Your body image and the way other people relate to you can take quite a lot of adjusting to.

Learn more


Reviewed by

Dr Andrew MacCormick is Associate Professor at Waipapa Taumata Rau (University of Auckland) and Upper GI and Bariatric Surgeon at Counties Manukau DHB. He has private practice rooms at Ormiston Surgeons, 125 Ormiston Road, Flat Bush. 09 277 8249, info@ormistonsurgeons.co.nz
Credits: Health Navigator Editorial Team. Reviewed By: Dr Andrew MacCormick, Associate Professor/Upper GI and Bariatric Surgeon Waipapa Taumata Rau (University of Auckland)/Counties Manukau District Health Board Last reviewed: 21 Feb 2022