NEW YORK (Reuters Health) - Fast-food patrons in New York City are eating far less unhealthy fat since restrictions on its use by restaurants were imposed four years ago, according to a new report sponsored by the city.

Trans fats, especially common in so-called hydrogenated vegetable oils, have been linked to long-term heart disease risk. The new study, which found the average meal went from containing nearly three grams of trans fat to just half a gram, doesn't prove the regulations will prevent heart disease or early deaths.

Still, researchers said it's a good sign for the potential of public health initiatives aimed at improving nutrition.

"It's a small step forward," said Alice Lichtenstein, a nutrition science researcher from Tufts University in Boston, who wrote an editorial accompanying the study in the Annals of Internal Medicine.

"This is just trans fat. It doesn't have any effect on calories; it doesn't mean that you can eat as much of it as you want," she told Reuters Health.

"We have to think about these changes within the context of the whole diet. This is one small change in the right direction. We need a whole lot more."

In 2006, New York City passed regulations prohibiting restaurants from serving food that contains partially hydrogenated vegetable oil and has half a gram or more of trans fat per serving. Those restrictions went into effect in 2008.

To test the policy's result, researchers briefly surveyed customers leaving 168 different fast-food restaurants, belonging to 11 popular chains, the year before and the year after the restrictions were first enforced.

Those chains included McDonald's, Burger King, Subway, KFC and Pizza Hut.

Based on receipts from 6,969 customers surveyed in 2007, the average fast-food meal purchased that year had 2.9 grams of trans fat. By 2009, that fell to 0.5 grams in a sample of 7,885 customers.

The number of meals without any trans fat increased from 32 percent of all purchases before the regulations to 59 percent afterward.

What's more, there wasn't a large spike in the amount of saturated fat in fast-food meals during the study period - as some had feared - so the total amount of "bad" fats in the average purchase dropped substantially.

Trans fat is "fully replaceable with healthier oils, so we knew that was something that could be changed," said Christine Curtis, from the New York City Department of Health and Mental Hygiene, who worked on the study.

"We were really pleased," she told Reuters Health. The study "really demonstrates that local regulation can reduce exposure to trans fat."

Curtis said the trans-fat regulation could end up leading to health benefits down the line. "It does have the potential to have a really big impact on cardiovascular disease risk," she said.

But Lichtenstein was more hesitant about inferring an effect on heart health.

"We can't expect this to suddenly translate to a decrease in heart disease rates," she said. "But with a lot of small steps, hopefully we will see a benefit."

Lichtenstein said cutting back on sodium in restaurant food and using leaner meat are two other strategies that could make eating healthier food "the default option" for restaurant-goers in New York.

And the researchers agreed that based on the success of the fat restrictions, other cities can take a lesson from New York and make their own dining options healthier, at least in one way.

SOURCE: Annals of Internal Medicine, online July 16, 2012.