Millions of people are being “overdiagnosed” as overweight or obese as scientists say there are problems with the main BMI measure.
Body mass index has long been used to categorise people but needs a “radical overhaul” according to 50 experts from around the world on a new Lancet Commission. BMI divides a person’s weight by the square of their height and currently shows around two thirds of adults in Britain are overweight or obese.
But some people with bigger frames may be very active and have no ill-effects of their weight but are still classified as obese while others may be suffering significant harm such as problems with their internal organs. Meanwhile other experts said around one in ten “lean” people may be “metabolically obese”.
Waist to height ratio could also be used to decide on obesity, experts say
(
Image:
Getty Images/iStockphoto)
Professor Francesco Rubino, chairman of the commission and chairman of metabolic and bariatric surgery at King’s College London, said: “Some people who are today classified as having obesity by BMI but they might play sports, they’re very active, they might have very strong bones – saying that those people have obesity and then classifying them as having a disease would obviously be an overdiagnosis.
“Everybody has been using the old classification for four decades but we are calling for a change, a radical change, because obviously, in the context of one billion people being classified as having obesity in the world today, and with a number that is projected to increase, no country is rich enough to be able to afford inaccuracy in the diagnosis of obesity.”
They said that “BMI is useful but we need to go beyond BMI to determine excess body fat” obesity should only be diagnosed using BMI when clinicians also take other measurements such as waist to hip ratio or waist to height ratio. They said that ideally obesity would be measured with body scans assessing total body fat, but the academics conceded this was not practical for the NHS to offer this widely.
Around two thirds of British adults are overweight or obese
(
Image:
Getty Images/iStockphoto)
Body mass index (BMI) categories are as follows:
- Underweight: BMI is less than 18.5 kg/m2
- Healthy weight: BMI is between 18.5 and 24.9 kg/m2
- Overweight: BMI is between 25 and 29.9 kg/m2
- Obese: BMI is between 30 and 39.9 kg/m2
- Severely obese: BMI is 40 kg/m2 or more
Prof Tom Sanders, expert in nutrition and dietetics at King’s College London, said the current BMI has been a useful indicator when looking at whole populations. The proportion of adults with a BMI greater than 30 has increased from around 15% in 1991 to around 29% now. Prof Sanders added: “BMI is currently used to define obesity and while it is useful for looking at groups of people it can be misleading in the range of BMI 25-34.9. For example there are a few individuals who are muscle bound and have low levels of body fat but have a BMI in the range 30-35.”
Big bones?
(
Image:
Getty Images)
Dr Adam Collins, Associate Professor of Nutrition, University of Surrey, said: “This paper is robustly laying bare the flawed assumption that body mass for size is, by itself, a marker of health. However it is also important to note that focusing solely on BMI as a marker of health, even with this suggested differential diagnosis, does miss other individuals who may be at risk despite a normal BMI.
“Those who can be described as ‘metabolically obese’, and who exhibit similar or greater metabolic risk than those who are obese. This may represent up to one in ten ‘lean’ individuals who would otherwise go undetected. This emphasises the need for more routine measures of risk, than simply BMI, to identify individuals at risk.”