Whether gastric sleeve surgery (sleeve gastrectomy) is an option for you depends mainly on your body mass index (BMI) and any related health problems. The five criteria below help you assess yourself before making a decision. The final assessment is always made by a specialist.
1. Understanding your BMI
The internationally accepted threshold for a gastric sleeve is a BMI over 40 kg/m², or a BMI between 35 and 40 kg/m² with related conditions such as type 2 diabetes or high blood pressure. Surgery is also considered for a BMI above 30 with type 2 diabetes or severe metabolic problems. These limits are also found in the guidelines of the American Society for Metabolic and Bariatric Surgery (ASMBS).
BMI is calculated by dividing your weight (kg) by your height (m) squared. For example, a person who is 1.65 m tall and weighs 110 kg has a BMI of about 40.4 kg/m². But weight alone can be misleading: fat distribution, waist size and muscle mass are also part of the assessment. So numbers alone are not decisive.
| BMI (kg/m²) | Category | Possible treatment (guide only) |
|---|---|---|
| 30 to 34.9 | obesity class I | surgery may be considered with type 2 diabetes or severe metabolic problems |
| 35 to 39.9 | obesity class II | surgery may be considered if there are related conditions |
| 40 to 49.9 | severe (morbid) obesity | gastric sleeve, gastric bypass |
| 50 and above | extreme obesity (super obesity) | gastric bypass or a staged surgical approach |
2. Obesity-related conditions
Obesity-related conditions are among the most important factors in deciding on surgery. Type 2 diabetes, sleep apnoea, high blood pressure, high cholesterol, fatty liver and reflux disease can all be reasons for an operation. For example, after a gastric sleeve some people with type 2 diabetes need less medication; this effect is well described in the literature on diabetes surgery. What matters is a joint assessment by the bariatric surgery team and specialties such as internal medicine, endocrinology, cardiology and respiratory medicine.
| Condition | Role in the decision to operate | Possible change after surgery |
|---|---|---|
| Type 2 diabetes | strong reason | blood sugar control may improve, need for medication may fall |
| High blood pressure | supporting reason | blood pressure may fall |
| Sleep apnoea | - | symptoms may ease, need for CPAP may fall |
| Fatty liver | moderate reason | liver values may return to normal |
| Reflux disease (GORD) | needs careful weighing up | a gastric bypass may be preferable; a gastric sleeve can make reflux worse in some cases |
Related conditions give the decision a meaning beyond body weight: the benefit of surgery only becomes clear when weight loss and improvement in metabolism are looked at together.
3. Previous attempts with diet and exercise
To be assessed for surgery, you are expected to have followed a structured diet and exercise programme under medical supervision for at least six months without losing enough weight for good. This requirement is set out in the guidelines. Repeated diets without lasting results are not a personal failure; there are physical reasons: insulin resistance, hormonal imbalances and genetic factors can make weight loss much harder.
In a gastric sleeve, about 80% of the stomach is removed. This reduces its volume and lowers the level of the hunger hormone ghrelin, so appetite control changes at a physical level.
4. Psychological preparation and realistic expectations
The long-term course depends not only on the operation itself but also on your inner preparation. A psychological assessment is a standard part of bariatric treatment. Eating disorders (especially binge eating disorder), depression that is not adequately treated, or an addiction must be treated before surgery. It is also important to understand that the operation is not a "miracle cure": lifestyle changes matter as much as the procedure. Going into treatment with realistic expectations gives you a sound basis for managing your weight in the long term.
5. Knowing the contraindications and risk factors
A high BMI does not automatically mean an operation is needed; some conditions can delay it or make other methods more suitable. The main possible contraindications (reasons not to operate) are:
- uncontrolled blood clotting disorders,
- advanced heart failure,
- ongoing cancer treatment,
- marked high pressure in the portal vein of the liver (portal hypertension).
In such cases, non-surgical methods may be considered; which option fits depends on your overall health. The ASA score (classification of the American Society of Anesthesiologists) is one of the tools used to estimate surgical risk.
Surgical methods compared
Which method suits you depends on your health, your goals and your surgical risk. The overview below is only a guide.
| Method | BMI (guide, kg/m²) | Duration of effect |
|---|---|---|
| Gastric sleeve | 35 and above (above 30 with type 2 diabetes or severe metabolic problems) | permanent; done under general anaesthesia |
| Gastric bypass | 40 and above, or with reflux disease | permanent |
Questions for self-assessment
The questions below can be a starting point before your first appointment with a doctor. You do not need to answer yes to all of them, but your answers will make the conversation with your surgeon much more useful.
- Is your BMI 35 kg/m² or higher, or above 30 kg/m² with type 2 diabetes or severe metabolic problems?
- Do you have at least one obesity-related health problem, such as type 2 diabetes, high blood pressure, sleep apnoea or joint problems?
- Have you changed your diet and exercise under medical supervision for at least six months without lasting weight loss?
- Are you ready to adapt your lifestyle after surgery (regular eating, a routine blood test at 6 months, exercise)?
- Are you free of a mental health condition or addiction that is currently being treated?
These questions do not replace a medical consultation, but they help you understand what to expect and ask the right questions. You can find answers to more questions in our FAQ.
Frequently asked questions
What age do you need to be for a gastric sleeve?
Under general guidelines, gastric sleeve surgery can be done between the ages of 18 and 65. Under 18, some centres may consider it if growth and development are complete and certain conditions are met. Over 65, the decision takes into account the medical risk profile and the expected quality of life.
Is surgery ruled out with a BMI under 35 kg/m²?
Surgery can be considered for a BMI above 30 with type 2 diabetes or severe metabolic problems. Without these problems, non-surgical methods are chosen more often for a BMI between 30 and 35 kg/m².
What tests are done before the decision?
Standard tests include blood tests, lung and heart tests, a sleep apnoea assessment, and a psychiatric and dietary assessment. A gastroscopy (a camera test of the stomach) is done if needed. These tests show whether surgery is suitable for you and help with personal planning for the time afterwards.
Gastric sleeve or gastric bypass?
The choice between the two depends on BMI, any existing reflux disease, how severe type 2 diabetes is and your general health. With reflux, a gastric bypass is recommended more often. A gastric sleeve is technically simpler and may therefore have advantages for certain higher-risk groups. Only a thorough medical assessment can show which procedure is right for you.
