Georgia Guldan, a nutritionist from Chinese University's biochemistry department, said this would be the most comprehensive study of its kind to be conducted in the city.

'Right now, if we find that certain kinds of fish, for example, are carrying toxins, we don't know who is eating them and how much, and whether that level of consumption is dangerous or not. We need to know who is at risk,' she said.

Professor Guldan, who is leading the survey, said at least three similar studies had been carried out on the mainland.

The Hong Kong study will be launched early next year and take a year to complete. She said common problems in the average Hong Kong diet were excessive amounts of fat and salt.

'Hong Kong is a modern city but people's knowledge about nutrition and health is still not up to date,' Professor Guldan said.

Philip Ho Yuk-yin, a consultant for community medicine at the department, said Hong Kong had been lagging behind the mainland and many overseas countries in this area of research.

'Much research into food has been conducted overseas, but there is limited information about the risk of various foods in a Chinese population,' Dr Ho said.

He said the Hong Kong study was also a response to an appeal by the World Health Organisation for more information on nutrition and food risks around the world.

The WHO has reported that dietary factors are responsible for about 30 per cent of cancers in industrialised countries. Diet-related factors such as poor nutrition, obesity and high blood pressure are also culprits in cardiovascular diseases.

The department regularly releases findings of its food research. In July, it released the results of a study into barbecued meat and found that many contain cancer-causing agents known as polycyclic aromatic hydrocarbons.