Before we had our surgery at Weight Loss Riga in March 2024, one of the first things we researched was whether we actually met the criteria. BMI thresholds come up quickly in any conversation about bariatric surgery eligibility. Here is what the guidelines say and what you actually need to know.
The standard NHS criteria
NICE guidelines set out the eligibility criteria for weight loss surgery in the UK. For bariatric surgery to be considered, the person must have a BMI of 40 or above, or a BMI between 35 and 40 with a significant obesity-related health condition such as type 2 diabetes, high blood pressure, or obstructive sleep apnoea. The guidelines also require that all appropriate non-surgical measures have been tried and failed to achieve or maintain clinically beneficial weight loss over a sustained period.
In 2022, NICE updated its guidance to lower the threshold for people from Black, Asian, and minority ethnic backgrounds, recognising that metabolic risk develops at lower BMI levels in these groups. For people from these backgrounds, surgery may be considered at a BMI of 35 or above, or between 27.5 and 35 with a significant comorbidity.
Private and overseas surgery
NHS criteria are designed for NHS commissioning decisions. Private providers and overseas centres apply their own criteria. Many private surgeons in the UK and abroad will consider patients with a BMI from 30 upward, with lower thresholds for people with metabolic disease. Weight Loss Riga, where we had our surgeries, assessed us as appropriate candidates based on our full clinical picture rather than BMI alone.
James was around 30 stone pre-operatively and well above the BMI threshold. Kirsten was around 18 stone. Both clearly met eligibility criteria. If you are close to the threshold and uncertain, the appropriate route is a consultation with a bariatric surgeon who can assess your full picture including health conditions, failed weight loss attempts, and risk factors.
Why BMI is an imperfect measure
BMI is a ratio of weight to height squared. It does not measure body fat percentage, distribution of fat, or the presence of metabolic dysfunction. Two people with the same BMI can have very different health profiles. Someone with a BMI of 38 who carries most of their weight as visceral abdominal fat, has pre-diabetic markers, elevated liver enzymes, and high blood pressure carries a very different risk profile from someone with the same BMI who carries weight more peripherally and has normal metabolic markers.
James had NAFLD approaching stage 3 liver failure, elevated liver enzymes, high blood pressure, and pre-diabetic markers. His BMI alone did not capture the full picture of what his weight was doing to his health. The surgical decision was driven by the clinical reality, not a number on a chart.
What happens if your BMI is below the threshold
If your BMI is below the standard threshold and you are seeking surgery on the NHS, you are unlikely to be offered it unless there are exceptional clinical circumstances. For private surgery, a frank conversation with a bariatric surgeon is the right starting point. Some surgeons will operate at lower BMIs, particularly where there is clear metabolic disease. Others will not. There is no single answer.
What the evidence does not support is surgery purely for cosmetic weight loss at low BMI without metabolic justification. The risks of any operation need to be proportionate to the benefits, and below certain weight thresholds the risk-benefit calculation shifts.
BMI at the upper end
Very high BMI, above 50 to 60, introduces additional surgical challenges and risks. Anaesthesia is more complex, positioning is more difficult, and the liver is often more significantly enlarged. Some surgeons will recommend a preliminary period of medically supervised weight loss before proceeding with surgery, both to reduce surgical risk and to test compliance and commitment. In some very high BMI cases, a more powerful procedure such as the duodenal switch may be recommended rather than sleeve alone.
Sources
NICE: Obesity: identification, assessment and management (NG238, 2022 update). NHS: Weight loss surgery eligibility. BOMSS: Commissioning guide for bariatric surgery.
About this content
This blog is written by James and Kirsten, a couple from the UK who had gastric sleeve surgery together in March 2024.
We started this blog because we couldn't find any sources of content that details before surgery, the surgery and then life post surgery - so we decided to write one ourselves.
Everything on this site is based on our own experience and the research we have done along the way. It is not medical advice. Gastric sleeve surgery is a serious procedure and every patient's journey is different. Please always consult your own bariatric team or GP before making any decisions about your health or treatment.
Some posts on this site may contain featured or sponsored content, or affiliate links. Where this is the case, it will always be clearly stated at the top of the article. Our opinions are always our own.
Publish Date: 29 May 2026 | Last Reviewed: 7 June 2026 | Next Planned Review: 7 December 2027