McDonald's is again facing the threat of obesity-related litigation after a US court ruled that part of a dismissed lawsuit against the fast-food chain could be reinstated.

The plaintiffs are four teenagers from the Bronx in New York who allege that eating McDonald's food caused weight and health problems. The food industry fears the case could trigger a new wave of lawsuits to rival those against tobacco firms.

The claim was filed in 2002 but US district judge Robert Sweet backed McDonald's motion for dismissal a year later. He said the plaintiffs failed to link health problems directly to McDonald's. He wrote: "If a person knows or should know that eating copious orders of super-sized McDonald's products is unhealthy and may result in weight gain, it is not the place of the law to protect them from their own excess."

But an appeals court said parts of the claim relating to deceptive advertising were admissible.