The criteria for weight-loss surgery need to be changed, according to health experts at the University of Gothenburg in Sweden. In particular, a reduction in the body mass index (BMI) that obese patients must exceed in order to qualify for weight-loss – or bariatric – surgery could result in improvements to the health of many more people, reducing the prevalence of conditions such as type 2 diabetes.

The recommendations are based on the findings of the Swedish Obese Subjects (SOS) study carried out at the university's Sahlgrenska Academy, involving 104 patients who were operated on despite their BMI being 'too low'. As a result, the risk of developing diabetes was reduced by 67%.

In both the UK and Sweden, bariatric surgery is currently only offered to patients whose BMI exceeds 40 for healthy patients, or 35 in combination with other risk factors such as type 2 diabetes; however, according to the researchers the selection criteria have not been devised in a scientific manner and need to be improved.

Researcher Kajsa Sjöholm from the Sahlgrenska Academy explained: "There is no proof that weight-loss surgery has a greater preventive effect against diabetes for patients who exceed today's BMI limit than for those who don't."

The study also showed that the surgery reduces the risk factors for cardiovascular disease among patients who are not currently eligible.

According to the researchers, strict BMI limits can lead to patients with a high risk of future disease who would benefit from treatment being denied surgery. Previous research findings show that the selection can be improved by analysing patients' insulin and glucose values.

Commenting on the arbitrary nature of the BMI limit, Professor Lena Carlsson from the academy's Institute of Medicine told European public sector science journal ScienceOmega.com: "These figures are based solely on the opinions of experts. No long-term studies have evaluated different cut-offs in terms of their treatment benefits: their capacity to prevent serious obesity-related problems. To supplement BMI, I think that we need to find additional criteria in order to direct resources to those who will benefit most from bariatric surgery."

The article, Evaluation of Current Eligibility Criteria for Bariatric Surgery: Diabetes prevention and risk factor changes in the Swedish Obese Subjects (SOS) study, was published in the journal Diabetes Care on 28 January.