Why BMI alone cannot be used to measure obesity

BMI cutoff values lack sensitivity

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Is obesity related to body mass index (BMI) alone? No. Experts believe this might not be the right approach. BMI is just a quick way to determine whether you are in a healthy weight bracket, but it does not provide the complete picture of a person’s health. By feeding in your height and weight, the numerous free BMI calculators available online tell you whether you are underweight, normal, overweight or obese.

Because of our genetics, even at a lower BMI, Indians carry excess fat, says noted endocrinologist Dr Shashank Shah.

Last August, the American Medical Association (AMA) discouraged doctors from relying on BMI alone to diagnose obesity. Researchers at Yale Medicine argue that BMI was developed based on the bodies of non-Hispanic white men; it may not provide accurate results for those who fall in other categories of sex, ethnicity, and race. This is why doctors insist that BMI should be used as a key factor, along with other parameters like blood pressure, cholesterol, and glucose level, to understand a person's overall health.

Obesity in India has reached a state where almost one in three people have some amount of excess fat in the body. Especially around the waist, which is often a precursor for chronic conditions like diabetes, heart and kidney disease, sleep apnea, and liver cirrhosis. Because of our genetics, even at a lower BMI, Indians carry excess fat, says noted endocrinologist Dr Shashank Shah.

BMI is essentially a number calculated by dividing your weight in kilograms with the square of your height in meters. As per the Centers for Disease Control and Prevention (CDC), BMI "is not intended to diagnose excess body fat or weight-related illnesses, such as high blood pressure, elevated cholesterol, and type 2 diabetes," all of which play a crucial role in weight management.

Recently, a paper by researchers at JAPI (Journal of the Association of Physicians of India) argued that “body mass index and waist circumference were both recommended for better identification of people at risk of obesity-related comorbidities than either of them alone.” The researchers added that the diagnosis and management of obesity should also consider a patient's psychology. The Edmonton Obesity Staging System (EOSS) was suggested as being most suitable for the assessment of obesity. A multidisciplinary team was considered invaluable for treating patients with obesity. The use of once-a-week semaglutide (2.4 mg) via the subcutaneous route was suggested as the first-choice anti-obesity treatment when pharmacotherapy is deemed necessary.

“An algorithm considering all these aspects was proposed,” stated the paper. “BMI assessment is one of the most common measures of obesity. However, it does not exactly measure/correlate with the total content of body fat; this is because the total content of body fat in two individuals having the same BMI could differ by a factor of two. Also, BMI cutoff values lack sensitivity in identifying adiposity (percentage body fat) and BMI evaluation is insufficient for identifying individuals with excess body fat percentage in 50 per cent of the cases.”

The paper noted that the BMI is between 25 and 32 in those who are otherwise not graded as severely obese, but the impact of obesity on the body in the form of joint disease, spine and body pain, inability to move, breathlessness, and inter-personal relationship problems are so severe that they deserve more aggressive treatment before they progress into obesity. This is not measured by BMI. EOSS acknowledges all three (metabolic, functional, and mental) aspects of obesity, and thereby offers a more well-rounded diagnostic and management system for it.

"Cardiologists and practitioners do approve this new system of grading obesity, which will help in its treatment,” says Shah. “It will initiate preventive action and timely therapy, and give scope for newer drugs to treat obesity in time.”