Body mass index (BMI) forms the basis for selecting suitable patients for bariatric surgery.

It is generally accepted that surgery is restricted to candidates with BMI greater than 35 kg/m2, or greater than 30 kg/m2with serious comorbidities such as type 2 diabetes.

This is based on the recently published joint statement by ASMBS and IFSO that replaces the long held 1991 NIH guidelines. The new guidelines now recommend metabolic and bariatric surgery for individuals with a BMI of 35 or more “regardless of presence, absence, or severity of obesity-related conditions” and that it be considered for people with a BMI 30-34.9 and metabolic disease and in “appropriately selected children and adolescents.”

But even without metabolic disease, the guidelines say weight-loss surgery should be considered starting at BMI 30 for people who do not achieve substantial or durable weight loss or obesity disease-related improvement using nonsurgical methods. It was also recommended that obesity definitions using standard BMI thresholds be adjusted by population and that Asian individuals consider weight-loss surgery beginning at BMI 27.5

BMI is just the start and there are many other important factors to consider in the assessment for suitability for bariatric surgery. You should have an appropriate level of general health and fitness and not have any mental or intellectual limitations that would make poor understanding of gravity of surgery and adherence to proposed dietary or lifestyle modifications a challenge. If you are currently an active smoker and have an alcohol or substance dependence, we recommend that, those issues be dealt with before considering bariatric surgery.

In our practice we accept anyone with a BMI over 35 kg/m2 or greater than 30 kg/m2 if there is an associated obesity related illness, such as diabetes, as suitable candidates for initial assessment.

Ethnicity and BMI

A WHO expert consultation reviewed scientific evidence that suggests that Asian populations have different associations between BMI, percentage of body fat, and health risks than do European populations. The consultation concluded that the proportion of Asian people with a high risk of type 2 diabetes and cardiovascular disease is substantial at BMIs lower than the existing WHO cut-off point for overweight. This raises the question, is it time to dichotomise classification of obesity by BMI to at least two categories; existing cut-offs for Caucasians, and different, lower cut-offs for Asian population?