Munching dark chocolate for all the health benefits it claims can do more harm than good, experts have warned.

A new study, which might not be appreciated by chocolate lovers, has dismissed earlier claims about dark chocolate being good.

Earlier researches had stated that plain chocolate was rich in flavanols, plant chemicals believed to protect heart.

An editorial published in The Lancet medical journal, however, alleged that many manufacturers removed flavanols from chocolate because of the bitter taste.

As a result, dark chocolate contained no flavanols but was rich in fat and sugar, both potentially harmful to heart and arteries.

Even if there were flavanols, ''the devil in the dark chocolate'' was the fat, sugar and calories.

An earlier study by Andreas Flammer of the Cardiovascular Centre, Zurich, had found that flavanol-rich chocolate caused blood vessels to open up and improved heart function in 11 heart-transplant patients.

Dark chocolate, however, might not necessarily contain flavanols since cocoa solids could be darkened after flavanols were removed.

'When chocolate manufacturers make confectionery, the natural cocoa solids can be darkened and the flavanols, which are bitter, removed, so even a dark-looking chocolate can have no flavanol,' the editorial suggested.

Consumers were also kept in the dark about flavanol content of chocolate because manufacturers rarely labelled their products with the information.

So with the holiday season around the corner, it might be worth getting familiar with the calories in a bar of dark chocolate versus a mince pie.