Up to eight million more adults in the UK could be classed as obese under a radical shake-up of the body-mass-index (BMI) system, experts have warned.
Under the current rules, a BMI score of 18.5 to 25 is healthy, 25 to 29 is overweight, and 30 or above counts as obese – the point at which the risk of serious illness soars.
But 58 international specialists have proposed an overhaul of how obesity is diagnosed, arguing BMI alone is too blunt a tool.
They suggest adding waist size and weight-to-height ratio to give a fuller picture of unhealthy body fat.
Now researchers from Harvard University and Massachusetts General Hospital, who examined data from more than 300,000 American adults, have found that adopting the new definition would expand the number of people classed as obese by almost 60 per cent.
In Britain, where around 13 million adults are currently obese, the same calculation could see that figure soar to nearly 21 million.
Experts called the findings ‘important’ and warned the ‘substantial rise in obesity prevalence’ could have ‘profound financial and public-health implications’.
Under the new rules, obesity would be defined as a BMI above 30 plus at least one raised measure, such as an increased waist circumference or waist-to-height ratio, or a BMI over 40.
Researchers labelled these subtypes of obesity as BMI-plus-anthropometric obesity.
People could also be deemed obese under the new rules if they had a BMI below 30 but at least two raised measures, which they called anthropometric-only obesity.
In the US study, 206,361 adults met the new criteria for obesity. Only 678 participants (0.2 per cent) who were previously obese by BMI no longer qualified because their other measures were normal.
Writing in JAMA Network Open, the Harvard and Massachusetts General Hospital researchers said: ‘The prevalence of obesity increased by 60 per cent when using the new definition compared with the traditional BMI-based one.
‘This rise was entirely driven by inclusion of individuals with “anthropometric-only obesity”,’ they added.
Around a quarter of all those classed as obese under the new definition fell into this group.
Although their BMI appeared healthy, these individuals had a significantly higher risk of organ dysfunction and diabetes than people without obesity – and were more than three times as likely to suffer organ damage, the scientists found.
The researchers also discovered that nearly 80 per cent of participants aged 70 or over were classed as obese under the new criteria – double the current rate.
‘Our findings support inclusion of anthropometric-only obesity within the new obesity definition,’ they concluded.
The definition was first proposed in January in a report by 58 global experts published in the prestigious Lancet Diabetes & Endocrinology journal.
They argued that BMI alone is not a sufficiently ‘nuanced’ way to assess obesity.
At the time, their recommendations were endorsed by numerous organisations, including the Royal College of Physicians.
It comes as a raft of long-awaited anti-obesity measures came into force earlier this month.
Under new Government laws, buy one, get one free deals on sweets, crisps, sugary drinks and other snacks have been outlawed in England, along with free refills of fizzy drinks in restaurants and cafés.
The crackdown will be followed in January by a ban on online adverts for unhealthy food and drink, and restrictions on TV advertising before 9 pm.
Ministers say the policies are designed to curb Britain’s growing obesity crisis.
A sobering report last year warned that Britain’s spiralling weight problem has fuelled a 39 per cent rise in type 2 diabetes among under-40s, with around 168,000 young adults now living with the disease.
Excess weight has also been linked to at least 13 types of cancer and is the second-biggest preventable cause of the disease in the UK, according to Cancer Research UK.
