New York City is a model of liberty, or perhaps anarchy, when it comes to political opinion, religion, clothing, body ornamentation, sexual proclivities and public etiquette. But even Gotham has limits. The city government -- which recently considered letting people officially designate themselves a sex different from the one indicated by their anatomy -- has decided it cannot stand by as citizens exercise their own choices about eating trans fat.

Why not? Judging from the allegations, because it's the worst food additive since E. coli. "It's basically a slow form of poison," charged David Katz, director of the Yale-Griffin Prevention Research Center. City health commissioner Thomas Frieden was not talking about radioactive polonium when he declared, "New Yorkers are consuming a hazardous, artificial substance without their knowledge or consent."

So this month, New York decided to forbid restaurants from using partially hydrogenated vegetable oils and shortening in cooking. This measure makes it the first city in the country to enact a ban -- edging out Chicago, which has been considering one since last summer at the behest of Ald. Edward Burke. He pronounced himself "disappointed" that his city is not the first to vigorously police food options.

Trans fat has the regrettable effect of raising levels of bad cholesterol in the blood and lowering levels of good cholesterol. Awareness of those properties is what motivated New York's City Council to legislate against them. But it has also brought about changes that show why the prohibition is unnecessary as well as unwise.

Most companies producing packaged foods began abandoning trans fat in 2004, partly in response to public concern and partly in response to pending federal rules requiring this ingredient to be listed on nutritional labels. Trans fat is most widely used in the fast-food industry, but even there, the shift has already begun. Wendy's has chucked it overboard, and KFC plans to end its use in frying next year. Trans fat used to account for 3 to 4 percent of the calories Americans ingest, but now, according to the American Council on Science and Health, it's down to 1 or 2 percent.

What all this proves is that scientific evidence shapes public understanding, and public understanding affects both corporate and consumer decisions. As the evidence against trans fat accumulates, companies that sell food have a powerful incentive (namely, sales and profits) to cut back on it, and customers have an equally powerful incentive (their health and longevity) to eat foods without it.

So today, you have ample choices. If you don't want your fries cooked in partially hydrogenated oil, you are free to patronize Wendy's. If you prefer the taste conferred by trans fat, and have no desire to attain your maximum possible lifespan, McDonald's will accommodate you.

In neither case do you need the City Council of New York, or any other government body, to ride up and yank the decision out of your hands. This is not some nasty contaminant that no one would conceivably want in their food. It's an ingredient with advantages and disadvantages, which different individuals will weigh differently.

If the problem is that people are consuming the stuff "without their knowledge or consent," as Frieden claims, then the reasonable step is to make restaurants provide the needed information. Instead, he refuses to let people eat trans fat even with all the knowledge and consent in the world.

The health benefits of the switch are probably exaggerated. As former Cato Institute policy analyst Radley Balko notes, the rise in consumption of trans fat over the past 20 years has coincided with a decline in the incidence of heart disease. As for obesity, the change is irrelevant, since trans fat has the same number of calories as any other type of fat. Switching from partially hydrogenated vegetable oil to canola or olive oil won't help you shed pounds.

Replacing trans fat with saturated fat, an option New York did not think to prohibit, would be even worse. Most experts agree that saturated fat is the biggest culprit in clogging American arteries. The Department of Health and Human Services has said, "Population-based studies of American diets show that intake of saturated fat is more excessive than intake of trans fat or cholesterol. Therefore it is most important for Americans to decrease their intake of saturated fat." (my emphasis)

But here's the good news: Even in New York, eating or not eating saturated fat is still up to you. Enjoy that freedom while you can.