The fat truth was discovered in a joint test by the Consumer Council and Centre for Food Safety.

"Trans fat has been linked to increased risk of coronary heart disease," said Anne Fung Yu-kei of the Centre for Food Safety. "It is believed to be even worse than saturated fat because it not only raises the level of bad cholesterol but also lowers good cholesterol."

Eighty food products including cakes, pastries, butter products and Chinese and Western fried food were tested from May to September.

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A sample of McDonald's large french fries collected in May contained 2.64g of trans fat, 120 percent of the recommended maximum daily intake of 2.2g.

McDonald's agreed to reduce its use and in a September sample found its fries only contained 0.11g of trans fat.

Among the three cream-filled shredded-coconut buns tested, one stood out from the rest with a low trans fat level of 0.39g.

Six food products including waffles with no filling, classic Chinese-style cakes, white sliced bread and shredded pork-filled egg rolls contained no trans fat at all.

"This shows the industry has the means and ability to lower trans fat levels in their food products," said council spokesman Ambrose Ho Pui-him. The difference in trans fat levels between these products are due to the ingredients used, Ho said.

Vegetable shortening and margarine are the main sources of trans fat as they can prolong shelf lives of the food and lower costs.

The council said people should use vegetable oil such as corn oil in cooking and that they should watch out for food with low trans fat but high in saturated fat levels.

For example, the council said, a large bag of french fries and two pieces of fried chicken may contain 70 percent of the WHO's recommended daily intake for a person with a daily energy intake of 2,000 calories.

In urging manufacturers to voluntarily label trans fat content of packaged food products, the council said: "This will allow the public to make an informed and healthy choice."

Chief executive of the council Connie Lau Yin- hing said: "We believe manufacturers will be happy to change their practices to cater to public demand for healthier food."

The council will distribute to manufacturers guidelines on the harmful effects of trans fat, and how to minimize its content in food products.

The council and the Centre for Food Safety will next collaborate on testing cookies, potato chips and fried spring rolls.