Weight loss surgery, also called bariatric surgery, is used to treat people who are dangerously obese.

This type of surgery is only available on the NHS to treat people with potentially life-threatening obesity when other treatments, such as lifestyle changes, haven't worked.

Potentially life-threatening obesity is defined as:

  • having a body mass index (BMI) of 40 or above
  • having a BMI of 35 or above and having another serious health condition that could be improved if you lose weight, such as type 2 diabetes or high blood pressure

Adults who have recently been diagnosed with type 2 diabetes may also be considered for an assessment for weight loss surgery if they have a BMI of 30-34.9. 

For people who meet the above criteria, weight loss surgery has proved to be effective in significantly and quickly reducing excess body fat. 

However, it's always recommended that you try to lose weight through a healthy, calorie-controlled diet and increased amounts of exercise before you consider weight loss surgery, as surgery carries a risk of complications and requires a significant change in lifestyle afterwards.

Because of these associated risks, most surgeons, whether they're working privately or for the NHS, would only consider someone for surgery if there was a clinical need, and not for cosmetic reasons.

Read more about who can have weight loss surgery.

Availability of weight loss surgery

Even if you're eligible for weight loss surgery, the demand on the NHS is currently higher than supply in many areas of the country. Therefore, there may be a considerable waiting list.

Weight loss surgery is also available privately. Prices are around: 

  • £5,000-8,000 for gastric banding
  • £9,500-15,000 for gastric bypass surgery

An increasing number of people are seeking treatment abroad, as costs for private treatment are often cheaper in other countries, but this should be considered carefully. For more information, see planned treatment abroad.

Types of weight loss surgery

The three most widely used types of weight loss surgery are:

  • gastric band – where a band is used to reduce the stomach's size, so a smaller amount of food is required to make you feel full
  • gastric bypass – where your digestive system is re-routed past most of your stomach, so you digest less food and it takes much less to make you feel full
  • sleeve gastrectomy – where some of the stomach is removed to reduce the amount of food that's required to make you feel full

Several other surgical techniques may be recommended in certain circumstances.

Read more about how weight loss surgery is performed.

Life after weight loss surgery

Weight loss surgery can achieve impressive results in terms of the amount of weight lost, but it shouldn't be seen as a magic cure for obesity.

People who have had weight loss surgery need to stick to a rigorous and lifelong plan afterwards to avoid putting weight back on or long-term complications.

This plan will include:

  • a carefully controlled diet
  • regular exercise

The rapid weight loss may cause relationship problems – for example, with a partner who is also obese – and it may lead to unwanted loose folds of skin, which may need further surgery to correct.

Many people with mental health problems, such as depression or anxiety, find that these problems do not automatically improve because they have lost weight.

It's important to have realistic expectations about what life after weight loss surgery will be like.

Read more about life after weight loss surgery.


As with all types of surgery, weight loss surgery carries the risk of complications, some of which are serious and potentially fatal, such as:

The overall risk of death in hospital after having any kind of weight loss surgery is around 1 in 1,000. Certain risk factors, such as high blood pressure or a BMI of 50 or above, also increase the risk of complications.

Read more about the risks of weight loss surgery.


As long as a person is willing and able to stick to their agreed plan afterwards, surgery can effectively reduce their weight and treat conditions associated with obesity, such as diabetes.

Recent research carried out in America found that, on average:

  • people with a gastric band will lose around half their excess body weight
  • people with a gastric bypass will lose around two-thirds of their excess body weight

Both techniques also lead to a considerable improvement (and sometimes a complete cure) of obesity-related conditions, such as diabetes or high blood pressure.

Read more about the results of weight loss surgery.

BMI and obesity

The most widely used method of seeing if you're a healthy weight is to calculate your BMI. This is your weight in kilograms divided by your height in metres squared:

  • If your BMI is 25-29.9, you're over the ideal weight for your height (overweight).
  • If your BMI is 30-39.9, you're obese.
  • If your BMI is over 40, you're very obese (known as morbidly obese).

BMI doesn't provide an accurate assessment of weight in all circumstances, such as in people who are very muscular or children going through a sudden growth spurt.

Page last reviewed: 26/03/2015

Next review due: 26/03/2017