One of the first questions I am often asked by patients considering weight loss surgery is: “Is my BMI high enough for surgery?”
The answer is not quite as simple as it used to be.
In Australia, bariatric surgery is generally considered for adults with a BMI of 40 or above, or a BMI of 35 or above together with a significant obesity-related health condition. However, international guidelines have changed in recent years, and metabolic surgery is now being considered at lower BMI levels in selected patients.
After almost 2 decades of assessing patients for weight loss surgery, I see BMI as an important starting point, but not the whole decision. Your health, weight history and previous treatment all matter.
What BMI is generally used in Australia?
As a general guide:
| BMI | When surgery may be considered |
| 40 or above | Surgery may be considered even without another obesity-related health condition |
| 35 or above | Surgery may be considered when there is a significant obesity-related health condition |
| 30–34.9 | Metabolic surgery may be considered in selected patients, particularly those with type 2 diabetes or other significant metabolic problems |
For Medicare purposes, the MBS defines clinically severe obesity generally as a BMI of 40 or more, or a BMI of 35 or more with major medical comorbidities. The MBS also recognises that health risks can occur at different BMI levels in different population groups.
These figures are a guide to when surgery may be considered. They do not mean that everyone above a particular BMI should have surgery.
Wondering where you fit in? Check Your BMI
The guidelines have changed
For many years, the commonly quoted criteria for bariatric surgery were a BMI of 40 or more, or 35 or more with an obesity-related condition.
In 2022, the American Society for Metabolic and Bariatric Surgery (ASMBS) and the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) published updated international recommendations. These guidelines recognised the growing evidence supporting metabolic surgery and moved away from relying solely on the older BMI thresholds.
The updated recommendations state that metabolic and bariatric surgery is recommended for people with a BMI of 35 or more, regardless of whether they have an obesity-related health condition. They also recommend surgery for people with type 2 diabetes and a BMI of 30 or more, and say that surgery should be considered for selected people with a BMI of 30–34.9 who have not achieved substantial or lasting improvement with non-surgical treatment.
Further evidence published by ASMBS and IFSO in 2024 supported these updated recommendations, including consideration of surgery for selected patients with BMI 30–34.9 and obesity-associated medical problems.
This is an important distinction for Australian patients: international clinical guidelines and Medicare eligibility are not necessarily the same thing.
What BMI do I need for a gastric sleeve or gastric bypass?
Meeting a BMI criterion means you can be assessed, not that surgery is automatically the right choice. Surgery is considered as part of a broader plan for your health and is decided by a surgeon working with a wider team. Age, previous weight loss attempts, current medications, other health conditions and readiness for long-term follow-up are all taken into account, and not everyone who could have surgery will be suitable for it. This kind of individual assessment is what a consultation at MBSA is designed to provide.
The BMI criteria for gastric sleeve surgery, gastric bypass and mini gastric bypass (one-anastomosis gastric bypass) are broadly based on the same principles.
A procedure may be considered at a BMI of 40 or above, or from 35 when significant obesity-related health conditions are present. In selected circumstances, metabolic surgery may also be considered at a lower BMI.
The BMI itself does not determine which operation is best. Different procedures have different effects, risks and considerations, so the choice needs to take into account your health, eating patterns, reflux symptoms, diabetes and other medical factors.
Why isn’t BMI the only thing we look at?
BMI is useful because it gives us a simple way of describing the severity of obesity. But it does not tell us everything about an individual patient’s health.
When I assess someone for bariatric surgery, I also want to know how long they have struggled with their weight, what they have already tried, whether they have conditions such as diabetes or sleep apnoea, what medications they are taking and how their weight has changed over time.
We also need to consider whether surgery is appropriate for that particular person and whether they understand the lifestyle changes and ongoing follow-up involved.
In other words, the number on the scales is important, but it is only part of the picture.
What if my BMI is 40 or higher but I don’t have diabetes?
You may still be suitable for surgery.
A BMI of 40 or above can meet the usual criteria for consideration of bariatric surgery even if you do not currently have diabetes, high blood pressure or another diagnosed obesity-related condition.
The absence of these conditions does not mean that obesity carries no health risk. It is also important to consider the longer-term risk of developing obesity-related disease.
What if my BMI is below 35?
This is where the newer recommendations are particularly relevant.
A BMI below 35 does not automatically rule out metabolic surgery.
For example, a patient with type 2 diabetes and a BMI of 30–34.9 may be considered for metabolic surgery, particularly when diabetes remains inadequately controlled despite appropriate medical treatment. The ASMBS/IFSO recommendations also support consideration of surgery in selected patients in this BMI range when non-surgical treatment has not produced substantial or lasting improvement.
The appropriate threshold can also vary between population groups. BMI does not have exactly the same relationship with body fat and metabolic risk in every population, and the international guidelines specifically recognise this issue, particularly in Asian populations.
What if I lose weight before surgery?
This is another common concern.
Some patients worry that if they lose weight through diet, exercise or medication and their BMI falls, they will no longer be considered for surgery.
That is not necessarily the case.
Your current BMI is considered together with your previous weight, weight history, medical conditions and response to other treatments. Losing some weight before surgery is often encouraged and may be beneficial for your health and preparation for surgery.
If your weight has changed significantly, this is something we can discuss during your assessment rather than making a decision based on one measurement alone.
Does Medicare cover weight loss surgery?
Medicare may provide a rebate for eligible bariatric procedures when the relevant MBS criteria are met. However, Medicare does not cover the entire cost of private bariatric surgery.
Your out-of-pocket costs depend on factors including your private health insurance, hospital, surgeon, anaesthetist and other fees involved in your care.
Some patients may also be eligible for bariatric surgery through the public hospital system, although access and waiting times vary between hospitals and health services.
If you are considering private surgery, it is important to check your level of cover and any waiting periods directly with your health insurer.
So, am I eligible for weight loss surgery?
If you are wondering whether your BMI is high enough, the best way to find out is to have your individual circumstances assessed.
Your GP can discuss your weight and related health conditions with you and provide a referral where appropriate. A bariatric surgeon can then look at your medical history, weight history, previous treatments and overall health before discussing whether surgery is a suitable option.
At Metabolic & Bariatric Surgery Australia (MBSA), Dr Mani Niazi and Dr Ramin Mehdipour assess patients considering bariatric and metabolic surgery and provide surgical care at Knox Private Hospital in Wantirna.
If you are unsure whether you may meet the criteria, MBSA also offers a 15-minute eligibility call before a formal consultation.
The important thing to remember is that there is no single BMI number that determines whether surgery is right for you. The decision should be based on your health, your circumstances and the potential benefits and risks of treatment.
Frequently Asked Questions
What BMI do I need for weight loss surgery in Australia?
Generally, surgery is considered from a BMI of 40, or from 35 when significant obesity-related health conditions are present. Selected patients with a BMI of 30–34.9 may also be considered for metabolic surgery, particularly in the presence of type 2 diabetes.
What BMI do I need for a gastric sleeve?
The BMI criteria for gastric sleeve surgery are broadly the same as for other bariatric procedures. A sleeve may be considered from a BMI of 40, or from 35 when significant obesity-related health conditions are present. Lower BMI surgery may be appropriate in selected circumstances.
Can I have gastric bypass with a BMI below 35?
Potentially. BMI is only one part of the assessment, and metabolic surgery can be considered at lower BMI levels in selected patients, particularly those with type 2 diabetes or other significant metabolic disease.
Does Medicare cover gastric sleeve or gastric bypass?
Medicare may provide a rebate for eligible surgical services when the relevant MBS criteria are met. The amount you pay yourself depends on your health insurance and the fees charged by the hospital and treating doctors.
What if I have lost weight and my BMI is now lower?
Losing weight before surgery does not necessarily mean you are no longer suitable. Your surgeon can consider your current BMI alongside your previous weight, weight history, health conditions and response to other treatments.
