Numerous studies in the last three years have investigated the link between dietary calcium and obesity, with some demonstrating an inverse relationship - the higher an individual's calcium intake, the lower the weight.
Most recently researchers at the University of Tennessee showed that high-calcium, and especially high-dairy diets, could significantly enhance weight and fat loss in obese people already following a low-calorie regime.
But while the growing body of research suggests that calcium could be a valuable tool against the rapidly rising cases of obesity, scientists have not yet uncovered the mechanism behind this effect.
"There are still numerous gaps in our knowledge, such as how the mineral effects body weight and whether it is quantitatively important," Arne Astrup, head of the institute of human nutrition at the Royal Veterinary and Agricultural University in Denmark, told NutraIngredients.com.
One hypothesis for the mechanism, from Michael Zemel, a nutritionist at the University of Tennessee, suggests that it has to do with the actions of vitamin D. Data appear to show that the active form of vitamin D, called calcitriol, causes fat cells to create more fat. Calcitriol levels are raised with lower intake of calcium. Therefore, fat cells produce more fat on low calcium diets. By contrast, high-calcium diets suppress calcitriol and, as a consequence, promote the burning of fat.
Astrup also has a theory about the mechanism, which will be further investigated in a new, three-year phd programme at the Danish university. The researchers will also look at why calcium supplements do not appear to have any effect on weight loss.
"This may be because of the way they are taken once a day, rather than as part of a regular meal."
However dairy foods are already recommended as a good source of calcium to protect bone health and regular intake of low-fat dairy could be an easier intervention against obesity than supplements.
But Astrup cautioned: "For this to be included in dietary guidelines, we need very solid evidence but we are only just beginning to get there. It is certainly premature to tell people that they can slim on a dairy-rich diet."
He added that "calcium is the headline rather than dairy".