Cadbury is to launch Under 99 Calorie bars in a bid to tempt shoppers who are watching their waistlines.
They are smaller in size, but contain exactly the same ingredients as standard Cadbury bars from the Birmingham confectionery giant.
The Under 99 Calorie message will be shown on the front of Dairy Milk, Bournville Extra Dark and Dairy Milk Mint Chips' wrappers. The 17.5g bars are due to be rolled out across UK stores later this month.
Tony Bilsborough, UK and European media relations manager for Cadbury Trebor Bassett, said: "We understand that many people want to manage their calorie intake and this clearly-labelled bar helps them to do just that while at the same time enjoying genuine Cadbury's chocolate. It is about giving them chocolate they know, love and trust in a portion that is clearly labelled for them."
Half the energy in chocolate comes from fat, according to the British Nutrition Foundation. It also contains high levels of sugar which are linked to tooth decay.
Dr David Haslam, chairman of the National Obesity Forum, welcomed the smaller, re-packaged Cadbury's bars but said the chocolate could be made healthier.
"The calories being on the front is an improvement in their labelling, but it doesn't go far enough. They need to put the amount of sugar and saturated fat on there as well," he said.
"They should not only label it better but improve the contents by decreasing refined sugars and saturated fat."
Dr Hannah Theobald of the British Nutrition Foundation said it was not a good idea for chocaholics to cut out the confectionery entirely while dieting.
"It is sensible to make the bars smaller because it gives consumers more choice - if you haven't got the willpower," she said.
"We recommend that if people are dieting and they love chocolate then they should have a little bit.
"If you try to cut it out entirely then you are more likely to crave it and, in the long term, break your diet."