American researchers may have hit upon a way to lose weight without eating less or doing more exercise.
Dairy products contain calcium
They found teenage girls weighed less and had less body fat if they ate more calcium.
Just one cup of milk or a thumb-sized piece of cheese was enough to make a difference.
But UK experts say the findings could be explained by the fact that people who eat more calcium are likely to have a healthier diet overall.
University of Hawaii researchers asked 321 girls aged between nine to 14 to record everything they ate and drank and any calcium or multivitamin supplements they took.
They then checked the girls' weight and the amount of fat just above their hipbones.
Unsurprisingly girls who consumed more total calories and exercised less were heavier and had more body fat.
But when girls of similar age, height, maturity, calorie intake and exercise level were compared, those who consumed more calcium weighed less.
There is absolutely no evidence on which to base the statement that increasing calcium intake increases the body's ability to break down fat
Dr Margaret Lawson, Institute of Child Health
It made very little difference if the calcium came solely from dairy products or included calcium supplements.
Dr Rachel Novotny, who led the research, said as calcium intake increases, the body increases its ability to break down fat and decreases fat synthesis.
She said the study indicated even fairly small changes in calcium intake would have a positive effect.
But Dr Margaret Lawson, senior lecturer in paediatric nutrition at the Institute of Child Health, told BBC News Online: "There is absolutely no evidence on which to base the statement that increasing calcium intake increases the body's ability to break down fat and decrease fat synthesis."
She added: "A high calcium intake is a marker of a healthy diet.
"Those who eat more calcium are more likely to take a balanced diet containing calcium-rich foods including dairy products and cereals.
"Those with a low calcium intake probably take more foods such as soft drinks and confectionary - both low in calcium."
The research was presented to the American Society for Nutritional Sciences' Experimental Biology meeting in San Diego.