For chocolate-lovers feeling guilty about their indulgence it is the best kind of news - eating more can help keep you thinner.
Although chocolate contains more calories than many other foods, those who eat it regularly have less body fat than those who don't, a study shows.
Researchers suspect the calories in chocolate are not like 'normal' calories.
The ingredients in chocolate appear to make your metabolism work harder, which means they offset the fat that might otherwise have stayed around.
As a result, the metabolic effects of certain ingredients make chocolate a good slimming food because it is calorie- neutral, says the U.S. study.
The study, published last night, did not specify which type of chocolate was best.
But it appears to back up the claim by Hollywood star Katharine Hepburn about her slim physique when she said: 'What you see before you is the result of a lifetime of chocolate.'
Study leader Dr Beatrice Golomb, from the University of California at San Diego, said: 'Our findings appear to add to a body of information suggesting that the composition of calories, not just the number of them, matters for determining their ultimate impact on weight.
'In the case of chocolate, this is good news, both for those who have a regular chocolate habit, and those who wish to start one.'
The scientists investigated the chocolate-eating habits of 972 men and women with an average age of 57 for a study of statins - cholesterol-lowering drugs.
The participants did not have any known heart problems but were asked diet and lifestyle questions including: 'How many times a week do you consume chocolate?' Their Body Mass Index, which relates weight to height, was also recorded.
The surprising findings showed those who ate chocolate on more days of the week than average were statistically likely to have a lower BMI.
This was despite the fact that people who ate more chocolate did not consume fewer calories overall, or take more exercise. In fact they ate more. Chocolate consumption was associated with greater overall saturated fat intake from other sources.
Volunteers had an average BMI of 28 - meaning they were overweight - and ate chocolate on average twice a week.
The study did not look at what type of chocolate the participants ate or how much. As a result, no link was seen between the amount of chocolate eaten and either higher or lower BMI.
The researchers warn the study's findings may not apply to all products containing chocolate and do not rule out the possibility that some people can put on weight with frequent modest chocolate consumption.
But the results, published in the journal Archives of Internal Medicine, broadly fit with previous research on rats showing benefits from some chemicals found in chocolate, including speeding up the metabolism.
Epicatechin, one chemical derived from the chocolate ingredient cocoa, has been shown to boost numbers of mitochondria, the cells' energy-generating 'power houses'.
Mitochondria burn up calories and epicatechin reduced weight in rats whose calorie intake and exercise levels were unchanged. Another antioxidant ingredient theo bromine is a stimulant.
Other studies have found that the benefits of chocolate can include a drop in the risk of heart disease and strokes, a reduction in blood pressure and a cut in the risk of diabetes.
Daily Mail, London