Thirty per cent of men who described themselves as fit in a survey were actually overweight or obese. Doctors behind the study said the findings showed that Hongkongers had a misconception about body shapes because they tended to compare themselves with people around them who were equally unfit. At the other extreme, about 20 per cent of women who regarded themselves as fit were actually underweight, according to body mass index readings. For Asian people, a BMI reading of 23 to 24.9 is classified as overweight, while 25 and above is obese. The survey of 500 men and women aged 18 to 60 was conducted by the public opinion programme of the University of Hong Kong and commissioned by the Obesity Awareness Alliance, a new group founded by four doctors. Co-convenor Dr Yeung Yat-wah said people lacked awareness of the health risks of obesity. "Fatter people are at greater risk of suffering from chronic diseases such as coronary heart disease and cancer," he said, adding that colorectal cancer was a particular hazard. People with abdominal obesity have a 60 per cent greater chance of developing colorectal cancer. Fellow co-convenor Dr Peter Tong Chun-yip said there was a simple measure to determine if you were overweight. "The waistline is a very good measurement to define whether people are fat or not," he said. A member of the alliance's committee, Dr Tony Lee Chun-kit, said obese people should focus on diet control and exercise to reduce their weight. He suggested they eat less salt, sugar and oil, and avoid late-night meals before sleeping. Another member, Dr Roman Chiu Chun-wai, said: "I recommend people have a body check every year. If your body is fine this year, it does not mean it will be the same next year." Tong gave one example to encourage obese people of any age to get fit - a 40-year-old man who lost over 13kg in three months through exercise and diet. Young people are also a cause for concern. In January, an HKU study of 100,000 school pupils and university students revealed that a quarter were overweight or obese.