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The body mass index (BMI) has been a ubiquitous measure of excess weight and obesity for the past several decades. By comparing a person’s height to their weight, a simple calculation yields their BMI. This number is often used as a preliminary screening criterion for most weight-loss surgery procedures. A BMI of 30 or over suggests obesity, while a BMI of 40 is the threshold for morbid obesity.
Most practices will pre-qualify a patient by checking their BMI. According to National Institutes of Health and FDA guidelines, or guidelines from major international societies like ASMBS and IFSO, patients with a BMI of 30 or higher and obesity-related diseases (comorbidities) may qualify for specific procedures. Those with a BMI of 35 or over with obesity related diseases, or 40 or over regardless of comorbidities, may be eligible for any bariatric procedure, including gastric bypass, sleeve gastrectomy, Duodenal Switch and SADI. Qualification and suitability for bariatric surgery do not end with the BMI, however. In fact, a patient’s medical history and comprehensive pre-op testing will determine whether they are a good fit for the procedure. The goal of any surgical procedure is safety and effectiveness, and that is why pre-operative testing is taken so seriously.
BMI Limitations
It is important to note that the body mass index should be used only as a rough guide to calculate your eligibility for bariatric surgery. It can also be used as a weight loss success benchmark both before and after surgery. Importantly, the BMI is also somewhat inaccurate because it does not account for several factors, including gender, body composition (fat vs. muscle), and age. In addition, specific patient demographics, including those of Asian descent, may experience comorbidities at a lower BMI than others, and this must be considered when qualifying them for bariatric surgery. Each of these factors, if integrated into the calculation, would independently vary the BMI reading.
In fact, there is a significant movement to use other metabolic markers as ways to determine eligibility for intervention. For example, waist size is considered by many as a more accurate measure of risk of comorbidities due to obesity. Or recently, we’ve seen a push to change the definition of obesity entirely, which would so classify most Americans.
Testing Beyond the BMI
While the BMI is used as an initial qualification factor for GLP-1 therapy or bariatric surgery, ultimately, patients’ candidacy for surgery and surgical intervention will rely on several tests performed before their procedure. Depending on a patient’s general health, this may include pulmonary and cardiovascular testing, psychological testing, and more. Ultimately, while bariatric surgery is extremely safe, the risks of the procedure itself, as well as risks under anesthesia, increase with a higher BMI.
How To Use the BMI
By and large, the BMI is a good indication of your preliminary eligibility for weight loss surgery. Most people also benefit from the BMI as a tracking tool to gauge a starting point, and to help them see how far they’ve come after a weight loss intervention. However, it is only one of many criteria used to ensure that a bariatric procedure is right for you.
