New Zealanders' consumption of a harmful type of fat has declined sharply in two years, following the voluntary efforts of food manufacturers.

But these improvements in the food supply are threatened by the economic downturn because reducing the amount of trans fatty acids increases food industry costs.

Some fast-food outlets which switched to dearer frying oils containing less trans fat are considering switching back, says the regulatory agency Food Standards Australia New Zealand.

It believes the industry may need further encouragement to stay on track.

Trans fat is a small but particularly harmful part of the diet. It occurs in foods from cows and other ruminant animals - and in manufactured foods like some biscuits, where it can result from the addition of hydrogen to vegetable oils to make them solidify at room temperature and to make frying oils last longer.

It can lead to an increased level of bad cholesterol, which is linked to a higher risk of heart attack.

The transtasman food ministers' council has opted to stick with the current approach of no regulatory control on trans fats.

It based this decision on a survey by Food Standards, which credits voluntary food industry action with a 25 to 45 per cent reduction of trans fat consumption in Australia and New Zealand since 2007.

The average intake of trans fats in New Zealand is estimated to be 0.6 per cent of total energy in the diet. More than 85 per cent of New Zealanders are now estimated to have trans fat intakes below 1 per cent of total energy.

Less than 1 per cent is the population-level goal set by the World Health Organisation.

For the up to 15 per cent who are eating too much trans fat, foods like deep-fried fish, pastry and creamy-style pasta dishes are big sources.

The Heart Foundation's food industry nutritionist, Judith Morley-John, said last night: "It's very encouraging to see the reduction in trans fat in two years since the transtasman collaboration began."

* Trans fat sources

Foods which supply high levels of trans fatty acids:

Pastry products.

Creamy-style pasta dishes.

Cheese.

Popcorn.

Doughnuts.

Takeaway fried fish.