Review question

What are the long-term benefits and risks of different types of weight loss surgery (also called metabolic and bariatric surgery) to treat obesity and type 2 diabetes in adults?

Key messages

• In people with obesity and type 2 diabetes, gastric (stomach) bypass (i.e. Roux-en-Y gastric bypass and one-anastomosis gastric bypass) may be most beneficial for improving body weight, waist circumference, type 2 diabetes status and long-term blood sugar levels at least five years after surgery, but for one-anastomosis gastric bypass, we are very uncertain about the results.

• It is unclear whether the different surgical procedures have an effect on risks such as serious unwanted health effects and death from any cause at least five years after surgery.

• Larger and well-designed studies may help reduce the existing uncertainties and increase our confidence in the findings.

What are obesity and type 2 diabetes?
Obesity is a condition with too many fat deposits that can damage health. In type 2 diabetes, the body has difficulty controlling blood sugar levels because the hormone insulin does not work properly. Type 2 diabetes often occurs in people with obesity, and both conditions increase the risk of premature death and other health problems, such as cardiovascular disease.

How are obesity and type 2 diabetes treated?

Lifestyle interventions such as nutrition, exercise, and behavioural programmes, along with medicines, are often used first for weight loss and improvement of diabetes status. When these do not work well, metabolic and bariatric surgery may be considered as an additional treatment option. There are a number of different types of bariatric surgery:

• gastric (stomach) banding;

• gastric sleeve (removal of a part of the stomach);

• Roux-en-Y gastric bypass (RYGB);

• one-anastomosis gastric bypass, or mini-gastric bypass;

• gastric plication (folding to make the stomach smaller);

• biliopancreatic diversion with duodenal switch.

What did we want to find out?

• Which of the different types of surgery are the safest and most beneficial ones by comparing them with each other and with lifestyle and medication therapy regarding their long-term (at least 5 years follow-up) benefits and risks.

• Whether these surgical procedures improve body weight, waist circumference, type 2 diabetes status, long-term blood sugar levels, and quality of life at least five years after surgery.

• Whether surgery affects serious unwanted health effects, death from any cause, and type 2 diabetes complications over this period.

What did we do?
We searched for studies involving people with obesity and type 2 diabetes. We included studies that compared at least two different surgical procedures, or surgery with lifestyle and medication treatment. We summarised and compared all treatments using a method called network meta-analysis, and we rated our confidence in the results based on factors such as study methods and sample size.

What did we find?
We found 18 studies, including 15,282 people with obesity and type 2 diabetes. In 13 of these studies (including 911 people), participants were assigned randomly to two or more treatment groups. This is the best way to ensure that groups of people are similar. Five studies (with 14,371 people) used ‘real-life’ observational data. The studies investigated surgical procedures such as gastric band, gastric sleeve, Roux-en-Y gastric bypass, one-anastomosis gastric bypass, and gastric plication. We found that:

• Roux-en-Y gastric bypass, may improve body weight and likely reduce waist circumference compared with lifestyle and medication treatment in the long term.

• One-anastomosis gastric bypass and, to a lesser extent, gastric sleeve, may also improve body weight and waist circumference, but we are very uncertain about the results.

• Roux-en-Y gastric bypass, one-anastomosis gastric bypass, gastric sleeve, and gastric band may improve type 2 diabetes status, but we are very uncertain about the results.

• It is unclear whether the types of surgery have an effect on serious unwanted health effects or death from any cause.

• Roux-en-Y gastric bypass may reduce type 2 diabetes complications in the long term compared to non-surgical treatments, but we are very uncertain about the results.

• Roux-en-Y gastric bypass may improve blood sugar levels compared to non-surgical treatments.

• One-anastomosis gastric bypass and gastric sleeve may also improve blood sugar levels, but we are very uncertain about the results.

• RYGB and SG may lead to a greater increase in health-related quality of life than non-surgical treatments, but again, we are very uncertain about the results.

What are the limitations of the evidence?
Our confidence in the evidence is often low to very low because the studies included only small numbers of people, and the results for some outcomes, especially serious unwanted health effects, death from any cause, and type 2 diabetes complications, were based on very few events. Moreover, for several surgical procedures, there were not enough studies to be certain about the outcomes. It is important to note that rating our confidence in findings was based only on studies in which participants were randomly assigned to groups and did not include observational studies.

How up to date is this evidence?
This evidence is up to date as of June 2024.