Members of the public are oblivious to the health dangers posed by being overweight, according to a poll conducted by the Co-operative Pharmacy.
One in five people were unaware that excess weight could lead to heart disease or attacks, the poll found.
Those in their fifties or older were the least likely to be aware of their body mass index, though they were most likely to be at risk of heart disease, the chain warned.
When asked, two out of five people said they were obese or overweight while almost 10 per cent said they were underweight.
Around half of people concerned about their weight were unwilling to discuss the issue with a health expert, the poll found.
Co-operative Pharmacy clinical services manager Fiona Caplan-Dean said the company had highlighted a worrying trend of people who had weight problems but were unwilling to seek professional help.
"A wealth of health information and weight loss options are readily available but people clearly still feel embarrassed about discussing the issue with health experts," she said.
"It is of great concern that people don't know their ideal weight and that they are blissfully unaware of the serious health risks posed by being overweight," she explained.