It's not the kind of fact most food vendors want to showcase, but faced with sluggish demand for its burgers and criticism over preservatives in its products, McDonald's has launched a campaign to prove that its food does, indeed, rot.

The company seems to be responding to some negative press, including an online video purporting to show a 14-year-old hamburger which didn't look like it had gone bad.

"There have been a lot of online videos and photos touting the fact that when left out for an extended period of time, a McDonald's hamburger does not rot and that this is because they are laden with chemicals," food scientist Keith Warner wrote on McDonald's official website in response to a question.

"The reality is that McDonald's hamburgers, french fries and chicken are like all foods, and do rot if kept under certain conditions."

Restaurants don't usually splash out marketing dollars to promote the rotting of their food. But the campaign launched this month -- "Our food. Your questions" -- aims to do that and more.

"We are taking action to restore customer trust," Don Thompson, McDonald's CEO said in a news release issued on Tuesday after the company reported that profits fell by nearly one-third in the last quarter.

Health advocates, however, were not convinced that the new campaign can change the fortunes of one of the world's largest restaurant chains.

"Clearly, McDonald's is on a mission to make us believe that their food is natural and fresh, but consumers are not fooled so easily," Vicki Hird, spokeswoman for the health advocacy group Sustain, said in an email to the Thomson Reuters Foundation.

"Eating heavily processed fast food products will always be less nutritious and have greater levels of preservatives, flavourings and other additives compared to cooking from fresh from a known source."