BMI has never been the most accurate marker for Indians to measure obesity, as abdominal fat is the primary concern. Many Indians appear lean but still carry significant belly fat. Because of this, waist circumference serves as a better indicator.
Published Jan 22, 2026 | 7:00 AM ⚊ Updated Jan 22, 2026 | 7:00 AM
Waist circumference. (iStock)
Synopsis: A study revealed that the BMI, the standard tool physicians use to assess obesity, gives a misleading picture as people grow older. Obesity, measured by waist circumference, increases steadily with age until people reach their seventies or eighties. BMI, however, follows a different path. It climbs through adolescence and middle age, peaks around 50, then descends in older adults.
A man stands before his mirror each morning, tightening his belt one notch further than last year. His bathroom scale shows the same number it did a decade ago. His doctor nods approvingly at his stable BMI (Body Mass Index). Yet beneath this surface of reassurance, fat accumulates around his organs, invisible and unmeasured.
This scenario plays out in clinics across the world, where doctors rely on a measurement that fails to capture what happens inside ageing bodies.
A study tracking over 120,000 people for 16 years has revealed that the BMI, the standard tool physicians use to assess obesity, gives a misleading picture as people grow older.
Researchers from the Health Survey for England examined data collected between 2005 and 2021 from individuals ranging from 11 to 89 years old. They compared BMI against three measurements of waist size: waist circumference, waist-to-hip ratio, and waist-to-height ratio.
The findings, published in the International Journal of Obesity, expose a pattern that contradicts what clinicians observe in their practices. Obesity, measured by waist circumference, increases steadily with age until people reach their seventies or eighties. BMI, however, follows a different path. It climbs through adolescence and middle age, peaks around 50, then descends in older adults.
“When it comes to measuring obesity, body mass index or BMI has never been the most accurate marker for Indians. In our population, abdominal fat is the primary concern. Many Indians appear lean but still carry significant belly fat. Because of this, waist circumference serves as a better indicator,” said Dr Vidya Tickoo, consultant endocrinologist and diabetologist at Yashoda Hospitals, Hyderabad.
“BMI gives the impression that obesity risk reduces in later life, which contradicts clinical evidence,” the researchers wrote. “Central fat accumulation, especially visceral fat, continues to increase with age even when body weight stabilises or falls.”
Picture a woman in her sixties who has maintained the same weight since her forties. Her BMI suggests she faces a lower risk than she did 20 years earlier. Yet fat has shifted inward, wrapping around her liver, her kidneys, her heart. This visceral fat drives diabetes, cardiovascular disease and metabolic disorders. The scale cannot see it. BMI cannot measure it.
Dr Ravula Phani Krishna, senior consultant surgical gastroenterologist, explained the clinical pattern. “In Asians, particularly Indians, obesity largely presents as central obesity. This form is driven by visceral fat and is closely linked to metabolic syndrome. Many patients appear thin but have low skeletal muscle mass and a small abdominal bulge. These individuals may look lean, but they carry significant visceral fat.”
The study tracked not just individuals but generations. People born between 1919 and 2008 passed through the survey years, creating a tapestry of data across birth cohorts. The analysis revealed something striking: Ageing itself drives obesity trends far more than generational differences. People born more recently show little protection from obesity once researchers account for age.
Between 2005 and 2021, the proportion of people classified as high risk using the waist-to-height ratio climbed from around 24 percent to over 33 percent. Waist circumference and waist-to-hip ratio identified even more people at risk than BMI did.
Consider two men, both 65 years old, both with BMI readings that place them in the overweight category. One carries his weight in his chest and arms, built from years of manual labour. The other carries it in his belly, accumulated through decades of desk work. BMI treats them identically. Waist measurements reveal the difference.
Among the measurements examined, the waist-to-height ratio emerged as the most reliable indicator across all ages. Unlike BMI and other waist measures, it uses a single threshold regardless of age or sex. A person simply divides their waist circumference by their height. If the ratio exceeds 0.5, they face an elevated risk.
“The waist circumference cut-offs for Indians are lower than those for Caucasians. For women, a waist circumference above 80 centimetres indicates obesity. For men, the cut-off is 90 centimetres. This is a simple measurement that anyone can do at home,” Dr Tickoo said.
Dr Krishna added specific thresholds for severe cases. “In the Indian context, newer methods focus on central obesity and visceral fat rather than BMI alone. A waist circumference greater than 100 centimetres indicates severe obesity, regardless of body weight. A waist-to-height ratio above 0.5 signals high metabolic risk.”
“This study highlights that WHtR is a more universal measure of obesity and can provide consistent trends across men, women and children, as well as into older age,” the authors stated.
The researchers used a technique called age-period-cohort analysis, which separates three influences on obesity: Getting older, living through particular time periods, and belonging to specific generations. They found that age effects dwarfed the others.
The odds of having a high-risk waist-to-height ratio increased steadily from adolescence through old age. For females reaching 85 to 89 years, the odds stood nearly five times higher than for those aged 18 to 19. For males in the same age bracket, the odds climbed more than six times higher.
BMI showed a different trajectory. The odds peaked in middle age, then declined. For males, the highest odds appeared at ages 50 to 54. For females, they peaked between 65 and 69, then dropped.
This divergence matters because obesity brings diseases that accumulate with age. Diabetes does not retreat after 65. Heart disease does not reverse in the seventies. Yet BMI suggests risk diminishes precisely when these conditions proliferate.
The study also tracked changes over time. Between 2005 and 2021, obesity increased across all measurements, but the rise remained modest once researchers accounted for ageing. This suggests populations face rising obesity not primarily because recent generations live differently, but because more people survive into ages where fat accumulates around organs.
The findings also support recent updates to UK obesity guidelines, which now recommend using the waist-to-height ratio alongside BMI rather than relying on BMI alone. The authors warned that continued dependence on BMI could lead to underdiagnosis in older adults, delaying preventive care when people need it most.
“Given the superiority of WHtR over BMI, the implementation of WHtR as a standard measure for obesity should be encouraged both by clinicians when assessing overall health risk of obesity as well as in the wider community,” the authors wrote.
The study had limitations. Measurements of waist circumference began only in 2005, restricting the comparison period. More data went missing for waist measurements than for BMI, possibly because people find waist measurements more invasive. The 2021 data relied on self-reported BMI rather than physical measurements, though research suggests adjusted self-reports match measured values closely.
The sample reflected England’s demographics, with 90 percent identifying as white, preventing analysis by ethnicity. This matters because fat distribution varies across ethnic groups, affecting risk thresholds.
The researchers emphasised that obesity constitutes a disease in itself, not merely a marker for other conditions. Recent definitions from the European Association for the Study of Obesity and the Lancet Diabetes and Endocrinology Commission recognise obesity as a distinct disease caused by excess fat tissue.
“Our results also show that, between age, period and birth cohort, age plays a significant role in analysing long-term trends in obesity,” the authors stated. “While there is a slight but consistent increase in obesity over time, the similar odds across birth cohorts suggest that the substantial rise in obesity throughout an individual’s life could hinder the population’s capacity for healthy ageing.”
As populations age, the study concludes, obesity and related disease burden will likely rise further unless health systems shift focus from weight alone to where fat is distributed in the body. The man before his mirror needs more than his scale can tell him. He needs a tape measure.
(Edited by Muhammed Fazil.)
