By Nicole Brewer

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PHILADELPHIA (CBS) –When you place an order, you know what you want. But, do you know what you’re getting?

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Starting Monday, it will be mandatory for restaurants to post calorie counts on all menus and menu boards, as part of the Affordable Care Act.

“I actually feel good about that,” said Juanita, in town from Pittsburgh.

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“I don’t like to know honestly,” added Angela Gaspar of Philadelphia.

The federal health law, which affects restaurant chains with at least 20 stores, also applies to grocery and convenience stores, movie theaters, pizza delivery companies, even vending machines.

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New research suggests it will inspire healthier eating.

A study by the Cochrane Public Health Group found diners consume eight to twelve percent fewer calories when nutritional information is available.

“I think it’s definitely worth trying,” said Dr. Jennifer Nasser, a registered dietician and associate professor at Drexel University.

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“I think anyone committed to a reduced-calorie diet will find this very helpful. I think for the general public, it may not be as helpful because behavioral data says information alone doesn’t change behavior,” said Nasser.

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“If I’m going to eat pizza and expect to eat pizza, it’s not going to affect what I order,” said Christina, in town from Indiana.