pidemiological evidence suggests that calcium intake is inversely associated with weight gain. A number of mechanisms have been proposed for this observation, although the complete picture is still unclear. Some evidence suggests that a low calcium intake may cause the calcium paradox, whereby cellular calcium levels rise. This is turn may negatively affect insulin sensitivity and thus lead to abdominal weight gain and the metabolic syndrome. Alternatively the high calcium concentrations could increase lipogenesis and decrease lipolysis, thus negatively affecting the utilisation of fatty acids. Other more simplistic mechanisms have been proposed, and in particular, some studies have shown that calcium can increase fat excretion, thus decreasing the amount of energy absorbed from the small intestine. This is thought to occur through the formation of insoluble calcium-fatty acid soaps, which decreases the bioavailability of the fatty acids.
The ability of calcium to inhibit the absorption of fatty acids has been shown in a number of studies in the nutritional literature. For example, one study published in the International Journal of Obesity in 20071 investigated the effect of calcium supplements on the faecal elimination of fatty acids. Isocaloric diets were fed to subject with calcium contents of 400, 1200 or 2500 mg from dairy products or 1200 mg from a calcium carbonate supplement for 7 days, in a cross-over design study. Compared to the 400 mg dairy diet, the 2500 mg dairy diet caused a 56 % increase in fatty acid excretion, although this difference was not significant statistically. The 2500 mg dairy diet also caused a decrease in the expression of fatty acid synthase mRNA, suggesting that lipogenesis may have been down regulated in this group. The 200 mg calcium carbonate supplements also caused a decrease in serum triglycerides.
Therefore the decrease in the bioavailability of fatty acids and alterations in the cellular lipogenesis to lipolysis ratio may explain the weight loss effects of calcium. Although the difference between the 400 mg and 2500 mg dairy diets of this study was not significant statistically, this may reflect the short-term nature of the study. In addition, other factors in the diet may influence the weight loss effects of calcium, but not enough is understood about the process to control for possible confounding variables. The authors also suggested that the high protein nature of the isocaloric diets may have inadvertently increased calcium absorption, thus decreasing the amount available for binding to fatty acids. Interestingly the best selling diet drug of the pharmaceutical industry (Orlistat) also works by preventing fatty acid absorption. However, calcium does the same without side effects, whereas Orlistat is known to cause significant digestive problems.