(CBS) – Fast food giant Taco Bell says it will take legal action against parties who filed a class-action lawsuit claiming the chain’s beef isn’t really beef. Taco Bell says the assertions in the suit are “false claims.”

Taco Bell, with 5,600 restaurants, said in a statement it is “proud of the quality of our beef and identify all the seasoning and spice ingredients on our website.”

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But a lawsuit filed in a California court claims Taco Bell menu items aren’t what they seem. The suit alleges products, such as beef tacos and burritos, advertised with seasoned beef actually contain a filling made up of mostly “non-meat substances,” including soybean oil and silicon dioxide, that wouldn’t measure up to United States Department of Agriculture standards for calling something beef.

Dee Miles, an attorney involved in the class-action suit, told CBS News, “According to the tests that we have taken, the taco meat filling is again about 35 percent meat.”

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According to CBS reports, some nutritionists have always been skeptical of fast food. Registered nutritionist Tanya Zuckerbort said, “If you’re thinking that you’re getting beef, but you’re actually getting something else, it could be putting your health at risk.

Customers at Taco Bell are given menu choices of chicken, beef or carne asada steak. According ot the complaint, “The ‘chicken’ and ‘carne asada steak’ served by Taco Bell is, in fact, chicken and carne asada steak. The ‘seasoned beef,’ however, is not beef.”

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Taco Bell President Greg Creed said buys the same brands of beef sold in supermarkets.