London: The scale of the British public’s denial about weight problems has been exposed in a new study that has revealed that more than a third of people who regard themselves as merely overweight are actually clinically obese, and at risk of major heath problems.

The study of more than 14,000 people across Europe found that more than a fifth of Britons who think their size is healthy or normal were in fact overweight.

The Association for the Study of Obesity [ASO], which commissioned the survey, said it underlined public ignorance about what represents a healthy weight.

Potential weight problems are indicated using the body mass index (BMI) a simple calculation of body fat based on height and weight.

Doctors define those with a BMI of more than 30 as obese, while those with a BMI of between 25 and 30 are considered overweight. A normal or healthy weight falls in a BMI range of between 18.5 and 25. Anything below that is considered underweight.

The study found that 36 per cent of adults in the UK with a BMI of 30 or more thought they were merely overweight. And, of those classed as overweight, 21 per cent thought their weight was normal.

Those in other countries displayed more awareness of their true weight. Only 10 per cent overweight Italians and 16 per cent of overweight French considered their weight healthy.

Of the Britons interviewed, 20 per cent were found to be obese, while a third were considered overweight. Only 5 per cent indicated they thought they were obese.

But Prof David Kerrigan, a bariatric surgeon who advises the NHS on obesity, said the study underreported the level of the problem because it was based on self-reported weight measurements. Clinical research suggests that about a quarter of people are clinically obese, he pointed out.

He said the research suggested there was a danger the public now thinks being overweight is normal.

Speaking to the Guardian, Kerrigan said: “We’ve almost become accustomed to people being bigger, because they don’t stand out. And that’s a problem because the true medical damage that obesity causes is internal and you don’t see it.”

He added: “It’s a silent killer: the narrowing of the arteries that cause stroke and heart disease, the impact of fat infiltrating glands like the pancreas and liver, resulting in type II diabetes, and the increasingly strong evidence linking obesity and common cancers.”

He urged the public to confront the reality of their weight and the potential health issues it can trigger. “Obesity isn’t a problem about how you look — that’s a side effect — it’s a problem about what it does to your insides.”

He also insisted the BMI was the best indicator of those carrying excess fat.

“There are weaknesses in using BMI as a measure of obesity, because there are exceptions such as the big beefy rugby players, where their BMI clearly doesn’t indicate an unhealthy level of obesity. But for the vast majority of the population it does work pretty well.”

The study comes a week after the World Health Organisation warned that almost three-quarters of men and two-thirds of women in the UK are risk of becoming overweight or obese in the next 15 years.

Prof Pinki Sahota, deputy chairwoman of the ASO, said the new government and health authorities should “greatly concerned” by the level of public denial about their true weight.

She said: “Obesity is one of the fastest-growing threats to the health and well-being of our society. And yet, this survey shows that many people still appear to have little understanding of what equals a healthy weight.

“It confirms much greater effort is needed to educate people about the fact obesity is a disease.”

The study, by Opinium, also revealed a gap between public perception about the causes of obesity and the medical consensus that it should be viewed as a medical condition requiring a range of treatments.

The 2,000 Britons interviewed were more likely than others in Europe to link rising levels of obesity to lifestyle choices such as overeating and lack of exercise, and failed to recognise other causes.

Sahota said: “It is clear the vast majority of people regard obesity as a problem purely of personal lifestyle, rather than recognising there are other underlying issues which society needs to address.”

Kerrigan agreed. He said: “You cannot separate the psychological component of obesity from the physical side. Simple gluttony is very unusual. For the majority of people it is in response to psychological or emotional stress.”