Evidence suggests that high intakes of dairy foods are associated with a lower level of body fat. In addition, it has been shown that high intakes of calcium are also associated with beneficial improvements in body composition. The calcium content of dairy could therefore be the reason for the association between dairy produce and body fat levels. Evidence suggests that increasing dietary calcium from 400 mg per day to 1200 mg per day decreases body fat and body weight by 64 and 70 %, respectively. Dairy foods could therefore have an antiobesity effect that has largely gone ignored by the general population and so called nutritional experts alike. Calcium is involved in intracellular signalling in adipocytes, and the calciotropic hormones, such as parathyroid hormone and calcitonin, may have novel roles in the regulation of adipose tissue. Mechanisms therefore exist to explain, at least tentatively, the association between high calcium intakes and improved body composition.
One hypothesis suggests that low calcium diet cause increases in the plasma levels of 1,25-dihydroxyvitamin D (calcitriol), and this causes an increase of calcium into the adipocytes, raising levels of calcium in the cell. Such a high levels of intracellular calcium in the presence of low plasma levels and low intakes is termed the calcium paradox. The high calcium levels in adipocytes may then stimulate lipogenesis, thus increasing adiposity. At the same time calcitriol may suppress expression of uncoupling protein 2, a protein that is tasked with wasting energy through conversion of substrates to heat. Suppression of this process decreases whole body thermogenesis and decreases energy expenditure. Low calcium diets may therefore raise plasma levels of calcitriol, and this in turn causes cellular changes that favour energy accumulation. If this is true it would tend to suggest that increasing calcium intakes in those with low intakes may cause weight loss without the need for energy restriction.
In fact calcium does appear to cause weight loss with no energy restriction. In a study investigating the effects of calcium on weight loss1, researchers randomly assigned obese subjects to a weight maintenance diet containing low (500 mg per day) or high (1200 mg per day) calcium from dairy foods, for 24 weeks. The results showed the high dairy diet caused significant fat loss (-2.16 kg), trunk fat loss (-1.03 kg), lowered insulin levels (18.7 pM), lowered systolic blood pressure (-6.8 mm Hg), lowered diastolic blood pressure (-4.25 mm Hg) and also caused an increase in lean mass (+1.08 kg). All of these changes were achieved without the need for energy restriction on the part of the subjects, and no such changes were observed in the low dairy group. In a second study, energy restriction was included with the high and low calcium diets. Although weight loss occurred in both diets, the weight loss was two fold higher in the high calcium group and the loss of lean mass significantly less.
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