Evidence suggests that individuals with higher intakes of calcium have improved body composition compared to those with lower intakes. However, the association between calcium and body fat is not understood. Because the main source of calcium in most diets is from dairy, it is not clear whether the beneficial effect is calcium specific, or dependent on some other factor present in dairy products. Milk does contain small amounts of conjugated linoleic acid (CLA), an isomer of linoleic acid that has been shown to be beneficial in weight loss (here). To help understand the effects of calcium on body composition, researchers1 used a prospective study design to investigate the micronutrient intake and anthropometric measurements of healthy exercising and sedentary women (18 to 31 years). Nutrient intakes were assessed with three-day diet records and body composition was measured by dual x-ray absorptiometry.
At the beginning of the study all the subject were selected because they were sedentary. Individuals were then randomly allocated to either an exercise group that performed resistance training 3 times a week with and additional 60 minutes of rope skipping, or were allowed to remain sedentary. Interestingly, after two years there was no significant difference in body composition between those who exercised and those who did not, save for a small increase in lean body mass in the resistance training group (+0.87 kg versus +0.19 kg in the exercise and non-exercise groups, respectively). Investigation of the diet records showed that there was no overall difference in nutrient intakes between exercise and non-exercise groups. Mean calcium intakes (781 mg/d) were below the current recommended intakes (1000 mg/d), and dairy calcium made up 69% of the total calcium intake.
The results of the study showed that calcium from dairy products was inversely associated with weight gain and body fat, irrespective of whether the individual was exercising or not. The inverse association between dairy calcium and body fat was only present in women who ate calories below the mean intake. Those women with higher intakes of energy did not gain a beneficial effect from increased calcium intakes. The best predictor of absolute changes in body weight and body fat were therefore total calcium intake and dairy calcium intake per calorie of energy ingested. Exercise appeared to have no bearing on this association. Another important finding of this study was that non-dairy calcium was not predictive of weight gain or body fat. These results support the hypothesis that high intakes of dairy products are protective of obesity (here).
Interestingly in this study, an association was also found between intakes of vitamin A (retinol equivalents) and weight gain, such that those individuals with the lowest vitamin A intakes had the lowest gain in body weight and body fat. Therefore subjects with the highest calcium and lowest vitamin A intakes per calorie ingested gained significantly less weight over the two year study period. The reason that dairy may be protective of obesity is perhaps due to the presence of CLA, as mentioned previously. However, animal studies suggest that non-fat diary products, that could not contain CLA, are also protective of obesity in mice. Calcium may therefore work via a different mechanism to improve body composition. High intakes of calcium may lower 1,25(OH)2D which may in turn decrease insulin release and increase lipolysis (here). Alternatively, low calcium intakes may cause pica, with the subsequent increase energy intake stimulating weight gain.