The city's ignorance of childhood obesity has been highlighted in a survey that has prompted doctors to call for people to wake up to the problem.
About half of the people questioned did not know that breast-feeding reduces the chances of children becoming overweight.
Around 40 per cent did not know that inadequate sleep led to childhood obesity.
And only one-third thought childhood obesity was a problem in Hong Kong.
Department of Health figures show that the obesity rate in the city's primary school children increased from 16 per cent in 1998 to 21 per cent last year.
The survey was carried out by doctors from the Federation of Medical Societies of Hong Kong, who called on parents to take the lead in having a balanced diet and doing regular exercise.
"Parents should set an example to prevent their children from being overweight," said Dr Raymond Lo See-kit, president of the federation, who announced the survey results yesterday.
Only 36 per cent of the 513 interviewees had children, but Lo said more people ought to be aware of such an important foundation of good health.
He said studies show breast-fed children are less likely to be overweight. More research was needed to find out why, but it is thought breast milk's lower sodium content compared to formula milk causes less stimulation of fat-making hormones.
He said it should also be well known by now that children needed 12 hours of sleep each day for protection from obesity.
A third of respondents were unaware that obesity may lead to emotional illness. Psychiatry specialist Dr Tony Lai Tai-sum said overweight children may have lower self esteem, and that some are teased or bullied.
Lo also warned of lesser-known complications caused by obesity, such as stomach acid reflux, obstructive sleep apnea and fatty liver disease.