Many of the above-cited papers, which compare dairy calcium with calcium supplements or calcium-fortified non-dairy food, show a somewhat greater effect of the former. This suggests that other milk components may modulate the weight-loss effect of calcium or have an effect of their own. These dairy components are possibly whey proteins and peptides, which may work synergistically with calcium to alter lipid metabolism and/or to affect postprandial satiety.
On the other hand, these studies also show that calcium has an anti-obesity effect of its own that is independent from other components of the diet. However, based on the results of the available positive studies and without exact knowledge of the mechanism, it is not possible to answer the question as to what extent this calcium effect is independent from the level of the 'normal' dietary calcium intake. According to our current understanding it could make sense to increase calcium intake above that of the recommended intake by using calcium-fortified food and/or calcium supplements in order to optimise intake for an anti-obesity effect.
In addition, the contribution of the different mechanisms (i.e. the Zemel mechanism versus the formation of calcium soaps) to the overall calcium effect is not clear, although answering this question may be of a certain relevance for the development of calcium supplements and calcium-fortified food. The use of highly water-soluble complex calcium salts and the addition of caseinophosphopeptides improves calcium bioavaila-bility, increases calcium absorption and thus promotes lipolysis, fatty acid oxidation and increased loss of lipids from adipocytes according to Zemel's hypothesis, while the formation of calcium soaps and thus the intestinal fat excretion would be reduced.
Independent of the answer to these questions, some quantitative information can be given to the extent of the anti-obesity effects of calcium. A quantitative re-analysis of the data from Davies and Heaney (Davies et al., 2000), using simple bivariate and multiple regression models, revealed that calcium intake accounted for ~3% of the variation in BMI in young women and that each 100 mg increment in daily calcium intake would decrease average BMI by 0.3 kg/m2 (according to a regression coefficient of 0.003). The apparent weakness of this association may be partly due to the fact, that the respective studies had not been designed to investigate the effect of calcium on body weight, but had skeletal endpoints. Indeed, other studies showed somewhat greater effects in adults (Table 11.2).
The actual importance of these effects becomes evident regarding population means (i.e. for weight, BMI or body fat). In young women, an increase in calcium intake by 600 mg/day from 500 to 1100 mg/day causes a drop in mean BMI of 1.8 kg/m2 (-8%), but decreases the predicted prevalence of overweight (BMI > 26 kg/m2) substantially by 78% from 16.6 to 3.6% and the prevalence of obesity (BMI > 30 kg/m2) by 84% from 0.99 to 0.16% of that age group (Heaney et al2002). Midlife weight gain decreased by 97% from 0.4 kg/year to 0.01 kg/year comparing women with 25% of the recommended calcium intake with those who had the recommended calcium intake (Heaney, 2003); 3.5-4.5% less body fat in pre-school boys and girls (body fat -18-21 %), correlates to one additional serving of calcium per day (300 mg), means a drop in body fat of -20% (Carruth and Skinner, 2001).
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