The ingredients for french fries are simple - potatoes and a cooking medium - but McDonald's US operation is enmeshed in a legal storm over unwelcome additions to its offering.

The fast food chain is facing at least three lawsuits claiming it has misled consumers following disclosures last week that its fries contain wheat and dairy flavorings.

At least two people, one in Illinois and one in Florida, are suing McDonald's after they allegedly became ill as a result of eating the fries, reports Associated Press.

Both consumers are said to have celiac disease, a condition sensitive to gluten contained in wheat. A Californian vegan is also going to court, saying she would not have eaten the fries had she known they contained a dairy product.

McDonald's denies its french fries have endangered those with wheat allergies. A statement from svp Jack Daly, states that testing shows the company's fries are "gluten free and allergen free".

He adds: "Based on this analysis, we believe the lawsuits filed are without legal merit."

However, the online menu has now quietly added "Contains wheat and milk ingredients" to the french fries listing.

Data sourced from USA Today Online and The New York Sun; additional content by WARC staff