The role played by calcium in maintaining correct bodyweight has been extensively reported in the literature. Epidemiological studies suggest an inverse association between calcium intakes and bodyweight, and both clinical trials and animal models show that calcium feeding is able to cause weight loss. The mechanisms by which calcium might regulate bodyweight are not fully understood but may involve appetite regulation by calitonin as well as increase cellular lipolysis, oxidation and thermogenesis in adipocytes due to suppression of 1,25-dihydroxyvitamin D. Research investigating the absorbance of calcium during weight loss in women has been undertaken because of the concern over the possible increased risk of osteoporosis with calorie restriction. These studies are useful in understanding the associations between energy intake and calcium metabolism and may give insights into the role played by calcium in bodyweight regulation.
Researcher published in the American Journal of Clinical Nutrition in 20041 investigated the effect of 6 weeks of weight loss on the absorption of calcium in 73 women with a body mass index of 26.9kg/m2. The subjects consumed either a diet that had a moderately reduced energy intake for their needs or a control diet designed to maintain weight. They were then randomly assigned to receive either 1g/d of calcium or 1.8g/d calcium in the form of calcium citrate. All subjects received a basic multivitamin and mineral in an attempt to standardise nutritional intake, and this contained an additional 200 mg of calcium. The energy restriction cause weight loss with an average of loss of 1.3kg (4.7%) of bodyweight. At baseline the total calcium fractional absorption (a measure of calcium absorption) was 7.4% and calorie restriction significantly decreased calcium absorption in the weight loss group.
Regression analysis showed that those with the greatest weight loss had the largest reductions in absorption and this resulted in those subjects in the lower calcium intake group to absorb insufficient amounts of calcium (195mg/d). However, the increased intake in the high calcium group maintained absorption to a sufficient level (348mg/d). Increased parathyroid levels in those women with insufficient calcium (weight loss group with low calcium) suggested compensatory hormonal adjustments for the low intake. These results show that energy restrictive diets decrease calcium absorption and as a result calcium absorption becomes insufficient. This is of concern in Western populations where insufficient calcium intakes are already common. Over the long-term, this calcium deficiency could cause increased resorption of calcium from bone. In addition, intracellular calcium ion concentrations could increase which would inhibit adipocyte lipolysis and oxidation and may make further weight loss difficult.
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