Practically everyone who has gone to a doctor for a check-up has had their BMI or Body Mass Index measured. BMI calculators abound online and it has become a modern go-to quick check for one’s health — financial services company Zerodha even announced, in 2022, an extra bonus for employees with a BMI of less than 25.
But how accurate is BMI in deciding how healthy you are now, or how healthy you will remain in the future? Increasingly, experts have arrived at the realisation that BMI is an imperfect calculation that has several limitations.
The new buzz word now, is BRI or the Body Roundness Index. Devised by U.S. mathematician Diana Thomas, and first published in a 2013 paper, this index measures how round you are. “BMI is grounded by the assumption that bodies are like cylinders. But when I looked at myself in the mirror, I thought — ‘I’m more of an egg than a cylinder.’ And this is what led to devising the BRI” she says.
The mathematical formula for BRI is associated with body fat levels, and takes into account height and waist circumference. The scores usually range from 1 to 15, with those having very high scores or very low scores (of over 6.9 or under 3.41) considered at the most risk for illnesses.
How is BRI different from BMI?
BMI is your weight in kilograms divided by your height in metres squared. A BMI of 18 to 24.9 is considered normal; 25 to 29.9 is termed overweight and 30 and above is classified as obese.
The problem, says Jaichitra Suresh, chief medical officer, SIMS Hospital, Chennai, is that BMI does not help a doctor understand the composition of the weight: how much of it is fat, muscles or water for instance, and where the fat is distributed in the body. “Athletic people and those who do weight training may have high BMIs, as muscles are denser than fat, but will still be healthy. It cannot be assumed that a high BMI always means high fat,” she points out.
BMI also has limitations with different ethnic groups — it was created using data from 19th century Europeans. For instance, Dr. Jaichitra says, an Indian and a Caucasian may have the exact same BMI, but in an Indian the fat percentage may be higher than that of the Caucasian.
How is BRI different? The BRI score takes the waist circumference into account, and calculates percent body fat: the calculator shows you an egg-like outline, with a green region, which is considered healthy. Scores outside this region are considered to be at risk. “The more round you are, the higher percent body fat you have, the higher your visceral adipose and therefore your risk of diabetes, cadiovascular problems etc. Metabolic illnesses can manifest without the body looking like it is obese. But even at the lower end, having a small body size for height, weight and gender, is a risk. The green zone shows you the sweet spot,” says Dr. Thomas, who is a full professor in the Department of Mathematical Sciences at the United States Military Academy, West Point.
Where does the fat lie?
When BMI was first proposed to be used as an indicator for mortality risk, experts pointed out that its scores may not be applicable for the Asian population — and at this stage, in 2002, it was suggested that 23 be considered an action point for concern for Asian populations, and not 25.
“But this,” says Anura Kurpad, professor of physiology at St. John’s Medical College who was part of the WHO expert consultation on BMI in Asian populations, which met in Singapore in 2002, “did not address the problem. It is not the amount of fat that is the issue but where the fat is — as fat in the abdomen, particularly when it accumulates around the internal organs, is what leads to metabolic syndrome and a host of medical issues. BMI can be misleading. You could be skinny but with a paunch and this would put you at risk of non-communicable diseases,” he says.
High levels of visceral fat (belly fat stored deep within the abdomen, around the internal organs) can contribute to developing type 2 diabetes, hypertension, cardiac diseases and other health conditions. Indians are genetically predisposed to putting on weight around the abdomen making them more susceptible to insulin resistance, and therefore, diabetes. The guidelines released this year by the National Institute of Nutrition reflect this: they state that BMIs ranging from 23 to 27.5 are to be considered overweight for Asians, since they tend to have a higher percentage of body fat compared to some other populations.
Alternatives were proposed then, says Dr. Kurpad, who is also senior advisor, Tata Trusts, including waist-height ratios. This is a simple index: if your waist circumference is less than half of your height, you are in good shape, but if it is more, then that indicates you are beginning to get spherical.
The problem of obesity is rising in India: according to the National Family Health Survey-5 (NFHS-5), the number of overweight/obese Indian men is now 22.9%, while the figure for women is 24%.
But Dr. Kurpad points to another issue as well: “BMI gives the impression that it is only physically overweight or obese people who are at risk of chronic diseases. But this is not true — thin people are also at risk, as are children. In fact a national nutrition survey in children aged 5 to 19 found that one in two children studied had higher than normal blood glucose levels, high BP and higher than normal cholesterol,” he says.
Even if adults or children are of normal weight, explains A.J. Hemamalini, professor and head of the department of clinical nutrition at the Sri Ramachandra Faculty of Allied Health Sciences, Chennai, often, their fat mass is high and their muscle mass is low, and this is why BMI is not always an accurate indicator. “We look at different components including biochemical profile, waist circumference, waist to height ratio and correlate this with dietary intake and physical activity, to arrive at an idea of their nutritional status,” she says.
More reliable alternative
Many studies have now shown that BRI may be better at predicting health risks than BMI.
In a paper published in Diabetology International in July 2021, researchers from JIPMER Puducherry noted that BMI’s clinical utility is challenged by its “inability to discriminate between fat and lean mass and failure to report the fat distribution.” The paper, ‘Cut-off values and clinical efficacy of body roundness index and other novel anthropometric indices in identifying metabolic syndrome and its components among Southern-Indian adults,’ by Chiranjeevi Kumar Endukuru et al, which studied 202 individuals, found that BRI, among other novel measures, had a “significantly higher predictive capacity to identify MetS (metabolic syndrome). Among traditional and novel anthropometric indices, the paper said, BMI and ABSI (a-body shape index) “exhibited the weakest predictive power to identify MetS in both genders.”
A recent cohort study of over 32,000 U.S. adults, ‘Body Roundness Index and All-Cause Mortality Among US Adults’ published in JAMA Network Open, found that the “association between BRI and all-cause mortality followed a U-shape, with both lowest and highest BRI groups experiencing significantly increased risk of all-cause mortality,” indicating that “BRI may be promising as a newer anthropometric measure associated with all-cause mortality.”
But how reliable is BRI? It may be subject to human error. Writing for The Conversation last year, Alice Bullas, Senior Research Fellow, Sports Engineering Research Group, Sheffield Hallam University, said one study had found that eight out of 10 trained health professionals demonstrated such high levels of human error when manually measuring the abdomen that they failed to notice an increase of 3 cm the second time they took the measurement. “This margin of error will probably be even higher in people taking their own measurements at home,” she wrote, adding that as a new metric, BRI also does not yet have the kind of extensive data backing up its use that exists for BMI.
While BMI, BRI and other indices to measure health risks may continue to be debated for some time to come, it’s a good idea, says Dr Kurpad, for everybody to use the simple waist to height calculation to keep track of their health.
Published – September 25, 2024 08:30 am IST