Nearly 80 percent of Americans say they check food labels for things like fat, calories and sugars. (Associated Press)

U.S. federal health officials say nutritional logos from food manufacturers may be misleading consumers about the actual health benefits of snack foods and other processed foods.

Manufacturers, including Kraft Foods and General Mills, rolled out their so-called Smart Choices program last year, amid growing concern about obesity rates. The green labels appear on the front of boxed foods that meet certain standards for calories per serving and number of servings.

But consumer advocates complain about lax standards for the program, with logos appearing on everything from frozen sweets to sugary cereals.

For example, Peppercorn Ranch SunChips packaging is stamped with a red heart, indicating that it's a good source of whole grains. Cocoa Krispies packaging has a banner saying the vitamin-enriched rice cereal will boost your immunity.

And Country Crock margarine containers bear a green label deeming it a Smart Choice.

The Food and Drug Administration has issued a letter to companies that says the agency will begin cracking down on inaccurate food labelling.

Earlier this year, Kellogg was reprimanded in the U.S. when it used the results of a study to advertise Frosted Mini-Wheats cereal as "clinically" shown to improve a child's attentiveness by 20 per cent.

The U.S. Federal Trade Commission, a government agency that regulates marketing claims, prohibited Kellogg from making similar claims about its breakfast and snack products, saying the study was not satisfactory.

With files from The Associated Press