One in four overweight women think they are thin because obesity has become so common that the image of what is a healthy weight has been lost, researchers have warned.
An American study questioned over 2,000 women about their size, diet and exercise habits and took measurements. It found that many women were often unaware about whether they were a healthy weight or not.
Co-author Dr Mahbubur Rahman, of University of Texas, said: "As obesity numbers climb, many women identify overweight as normal, not based on the scale but on how they view themselves."
It was found that 25pc of overweight women misjudged their body weight along with 16pc of normal weight women.
The research was published in the journal Obstetrics and Gynaecology.
The findings have serious consequences for obesity prevention, the researchers said, as many women do not recognise they are overweight and so will not join programmes.
The study found that Hispanic and African American women who were overweight thought they were healthy compared with 15 pc of white women.
The trend was reversed for normal weight women who thought they were overweight with fewer Hispanics and African Americans falling into this category than white women.
Healthy weight women who thought they were too fat were twice as likely to skip meals, diet and smoke more cigarettes than the overweight women who thought they were slim.
Lead author Prof Abbey Berenson, said: "Weight misperception is a threat to the success of obesity prevention programs.
"Overweight individuals who do not recognise that they are overweight are far less likely to eat healthfully and exercise.
"These patients are at risk for cardiovascular disease, type 2 diabetes and other serious problems.
"This is especially important for reproductive-age women because they are more likely to be obese than similarly aged men, often because they've had at least one child and have not lost pregnancy weight and find that their schedules make it difficult to exercise and eat healthfully."