PHILADELPHIA —  Philadelphia is set to become the second large American city to ban restaurants from serving trans fats, which doctors say increase the risk of heart disease.

The City Council approved the ban unanimously Thursday, and Mayor John F. Street is expected to sign it. The measure would prohibit restaurateurs from frying foods in trans fats or serving trans fat-based spreads beginning Sept. 1.

By Sept. 1, 2008, trans fats would be banned in all other types of food prepared in Philadelphia eateries.

Doctors say trans fats — listed on food labels as partially hydrogenated vegetable oil — can raise bad cholesterol and lower healthy cholesterol.

New York City has a similar ban on trans fats that is also scheduled to be phased in beginning July 1.

Some chain eateries and institutions — such as Starbucks and university dining halls — have already done away with trans fats or sharply reduced their use.

Philadelphia's ban will be enforced by the Health Department, but it does not include penalties for violators. The ban will not apply to prepackaged foods sold in city stores and eateries.