New research shows that three in four people are unaware they have a weight problem as obesity is 'seen as the norm'.
According to a poll from Slimming World and YouGov, only seven per cent of people believe their weight problem is significant enough for them to be classified as obese.
Despite this, 27 per cent fell into the obese category.
Experts believe the results are due to a rapid rise in obesity, leaving ten million people unaware that their health is at risk.
The research has been released to coincide with Slimming World's 40th birthday and also found that over half of people who are obese believe they eat a healthy diet.
Dr Jacquie Lavin, Slimming World head of nutrition, said: 'People in the UK are getting heavier and that is likely to be having an effect on their perceptions of what qualifies as obese.
'For years experts have agreed that losing just ten per cent body weight can lead to significant improvements in health - but if people don't even realise they have a serious weight problem it can be difficult to address.'
Across the nation, the factors making people obese tend to vary depending on where people live. People in the north cited alcohol; Londoners said eating out; and Welsh people claimed that chocolate made them put on weight.
'While the general rise in obesity is causing people to underestimate the severity of their own weight problem, it's clear that many people do want to slim down and more than half of respondents say they would consider at least one weight loss option,' Dr Lavin added.