Health bureau raises cancer warning for stir-fried greens
Hongkongers are being urged to eat fewer stir-fried greens after a study found they account for half the local intake of a potentially cancer-causing substance.
Processed at the high temperatures created in a wok, vegetables such as zucchinis and green peppers can produce the toxic contaminant acrylamide, the Department of Health warned.
In excessive amounts, acrylamide can damage the nervous system and has been identified as a probable cause of cancer in humans, the department said.
The department's food safety officer Dr Xiao Ying said the findings on acrylamide intake "indicate a health concern", despite Hongkongers intake of the substance being lower than that of mainlanders and consumers in seven Western countries.
"The public can avoid the substance by cooking the food in a healthier way such as boiling or steaming," Xiao said.
"More acrylamide is formed when frying at a higher temperature and for a longer time, but it was not detected in non-fried items, including uncooked fruits and boiled vegetables."
The contaminant is formed during the high-temperature processing of food containing the amino acid asparagine - so named because it was first discovered in asparagus.
Dr Philip Ho Yuk-yin, the department's consultant on community medicine, said that although the amount of acrylamide required to be a risk to health had not been established internationally, people should keep their intake "as low as possible".
The findings came after an analysis of 133 common food items in the Hong Kong diet.
Stir-fried zucchini, water spinach (kangkong), green pepper, onion and garlic contained the highest levels of acrylamide, with up to 360 milligrams of acrylamide present per kilogram. Bitter melon, Chinese lettuce and watercress had the lowest, all with less than 10 milligrams.
The stir-fried greens are still healthier than snacks such as potato chips, crisp bread and crackers, which contain up to 680 milligrams in each kilogram.
From the study, the department estimated that the average Hongkonger is exposed to 0.21 milligrams of acrylamide in each kilogram of food they eat, while those who consume a higher than average amount of food may take in 0.54 milligrams.
But consumers on the mainland, the UK, Canada, Europe, the US, France, Ireland and New Zealand all have higher intakes of the substance. Mainlanders take in between 0.28 and 0.49 milligrams, the second highest intake.
Half of all daily exposure to the contaminant in Hong Kong comes from vegetables and their products while about 15 per cent comes from cereals and 4.7 per cent from snacks. Meat contributes only 2 per cent.
The study did not find an obvious association between the use of oil and the amount of acrylamide released during cooking.
"The discrepancy in exposure between the East and the West may be a result of their diet habits," Ho said. "Westerners tend to consume more potato chips and fried potatoes, which have high levels of asparagine."
Ho advised the public to eat at least three servings of vegetables a day, using moderate-heat cooking, and to avoid eating fried foods altogether.
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