Obesity’s new spin: is it time to say ‘bye BMI’?

The new definition of obesity takes into account not just the weight, but actual body fat and health of an individual.  (Pexels/Moe Magners)
The new definition of obesity takes into account not just the weight, but actual body fat and health of an individual. (Pexels/Moe Magners)

Summary

Obesity, a new report recommends, should be diagnosed by an individual’s body fat percentage, not weight, which was the norm

Obesity has a brand new definition now. This new description of the lifestyle disease—which goes beyond the currently accepted BMI (body-mass index) norms— has been proposed in a new report published in the The Lancet Diabetes & Endocrinology journal in early January. A multi-nation commission of doctors and experts, which included Dr Anoop Misra, executive chairman and director of diabetes and endocrinology at Fortis C-DOC Hospital in Delhi, in the report, titled Definition and Diagnostic Criteria of Clinical Obesity, noted that clinical obesity should be treated as an “illness that, akin to the notion of chronic disease in other medical specialties, directly results from the effect of excess adiposity on the function of organs and tissues."

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The understanding of obesity has evolved significantly over the past few decades, with particular attention to ethnic differences, says Misra. “In 2009, India introduced revised definitions of obesity specifically for Asian Indians. This revision acknowledged that Asian Indians typically have higher body fat percentages than Western populations and develop diabetes at lower BMI levels." Those new guidelines, Misra notes, set lower thresholds and established waist circumference thresholds. “Men with a waistline larger than 90 cm and women with waists greater than 80 cm, lower than Western standards of 102 cm and 88 cm respectively, were considered obese," says Misra, noting that contemporary approaches to obesity have moved beyond simple BMI measurements. 

In essence, the new definition of obesity goes beyond just weight and takes into account actual body fat and health of an individual. “We recommend that BMI should be used only as a surrogate measure of health risk… or for screening purposes, rather than as an individual measure of health," the commission members write, as the current BMI-based criterion can both underestimate and overestimate obesity. 

TWO STAGES OF OBESITY

The new classification system divides obesity into two distinct stages. Stage 1 is “innocuous obesity," which is characterised by increased body fat without any organ or metabolic dysfunction while Stage 2 is “obesity with consequences," which is marked by impact on physical functions and presence of obesity-related diseases. “This framework places special emphasis on abdominal fat distribution, which has a particularly adverse impact on Asian Indian populations," adds Misra. 

The relationship between elevated BMI or excess body fat and health complications varies significantly among individuals and the new definition of obesity takes this into account. “The Lancet Commission has introduced a more nuanced framework distinguishing between clinical obesity (accompanied by mechanical and organ dysfunction) and pre-clinical obesity (indicating increased health risk) without current illness. It emphasises that these guidelines will lead to more rational diagnoses and treatment," says Misra. 

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Since the turn of the century, obesity in India has doubled, with abdominal obesity becoming prevalent, and childhood obesity rates are also rising significantly, says experts. There have been concurrent increases in obesity-related conditions such as diabetes, lipid disorders, fatty liver disease, and cardiovascular disease. In this context, this evolution of the definition and classification of obesity carries significant implications as the new framework enables more precise and personalised treatment strategies that consider individual metabolic profiles and risk factors, adds Misra. 

The concept for BMI was first developed by Belgian sociologist, astronomer and mathematician Lambert Adolphe Jacques Quetelet in the 1830s. He created a metric based on height and weight of samples that exclusively included Western Europe white men. In 1972, American physiologist Ancel Keys, who studied the influence of diet on health, built on Quetelet’s work in his study that analysed a dozen samples of 7,426 men and formally coined the term, Body Mass Index. BMI is the ratio of weight in kilograms and square of height in meters. 

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WHY BMI IS NOT PERFECT

“BMI doesn’t account for factors like age, sex, race, ethnicity, bone density, overall body composition and muscle mass. It tends to overestimate obesity in shorter people and underestimate it in taller people. Also, a person who has significant muscle mass and less fat can have the same BMI as someone who has more fat and less muscle mass," says Dr Rinkesh Kumar Bansal, additional director for gastroenterology and hepatobiliary sciences, Fortis Memorial Research Institute, Gurugram. BMI also errs when it comes to people with physical disabilities who are unable to walk due to muscle wasting, Bansal points out. 

“Today, doctors and fitness professionals opt to use other metrics that present a truer estimate of health and fitness including body fat percentage, waist-to-hip ratio, blood pressure, physical fitness, cholesterol levels, and other similar metrics, which are considered good markers of health and fitness," shares Spoorthi S, Cult.fit fitness expert. 

A metric that’s getting popular is the Body Roundness Index (BRI), developed by New York-based mathematician Diana Thomas in 2013. BRI calculates the roundness of body shape using height and circumference of the waist and it ranges between 1 to 20 (1 being narrow and 20 being more round). “It’s considered a more accurate measure than BMI because it places greater emphasis on fat distribution, particularly belly fat, which is strongly linked to increased health risks," explains Spoorthi. 

Bansal cites a large retrospective study involving nearly 33,000 US adults in which researchers found that a higher BRI was associated with an increased risk of death from all causes. Overall, BRI offers a more accurate assessment of body composition and health risks in comparison than BMI, notes Bansal, adding that further validation is needed in India before fully adopting it. For now, however, one can presume that the new definition of obesity might finish off BMI for good. 

Shrenik Avlani is a writer and editor and the co-author of The Shivfit Way, a book on functional fitness.

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