WASHINGTON – Turns out it’s possible to make a fast-food lunch a bit healthier even without skipping the fries.

New York City now has hard evidence that its ban on trans fat in restaurant food made a meaningful dent in people’s consumption of the artery clogger and wasn’t just replaced with another bad fat.

The findings published today have implications beyond heart health, suggesting another strategy to curb the nation’s obesity epidemic.

By year’s end, the Food and Drug Administration hopes to finalize long-awaited rules that would make many restaurant chains post the calorie counts of their products on the menu. But New York’s trans-fat ban — later copied by more than a dozen other state and local governments — didn’t put all the onus on the consumer to do the right thing.

“By making the default option the healthier choice,” everyone benefits regardless of their nutrition awareness or willpower, Alice Lichtenstein, a nutrition specialist at Tufts University, wrote in a commentary on the research. “The regulation may serve as a model for future successful public health initiatives.”

Trans fat is widely considered the worst kind of fat for your heart, gram-for-gram more harmful than its better known cousin, saturated fat. Small amounts occur naturally in some meat and dairy products. But much of the trans fat we eat is artificially produced, by hardening liquid oils so they can be used for baking or a longer shelf life.

In 2006, the federal government began requiring that packaged foods list the amount of trans fat contained per serving, a boon for grocery shoppers who could finally tell which processed foods were more or less heart-healthy.

But restaurant fare remained a mystery. So New York City issued a first-of-its-kind rule restricting artificial trans fat in restaurants, forcing them to alter recipes so that foods contained no more than 0.5 grams per serving. The change affected customers beyond New York as big chains like McDonald’s wound up cutting the fat system-wide.

The latest study by the New York City Department of Health and Mental Hygiene shows the effect.

Researchers surveyed customers and collected receipts for nearly 15,000 lunchtime purchases at fast-food chains around the city in 2007 and 2009, before and after the ban was in place.

The amount of trans fat in each lunch sold dropped an average of 2.4 grams after the ban, researchers report in today’s edition of Annals of Internal Medicine.

The biggest drop, 3.8 grams, occurred in hamburger chains, followed by Mexican food and fried chicken chains.

The study found only a small increase in saturated fat, mostly in sandwich chains.