Regulation of adiposity and obesity risk by dietary calcium: mechanisms and implications.

Dietary calcium plays a pivotal role in the regulation of energy metabolism; high calcium diets attenuate adipocyte lipid accretion and weight gain during periods of overconsumption of an energy-dense diet and increase lipolysis and preserve thermogenesis during caloric restriction, thereby markedly accelerating weight loss. Intracellular Ca2+ has a key role in regulating adipocyte lipid metabolism and triglyceride storage, with increased intracellular Ca2+ resulting in stimulation of lipogenic gene expression and lipogenesis, suppression of lipolysis, and increased lipid filling and adiposity. Moreover, we have recently demonstrated that the increased calcitriol released in response to low calcium diets stimulates Ca2+ influx in human adipocytes and thereby promotes adiposity. Accordingly, suppressing calcitriol levels by increasing dietary calcium is an attractive target for the prevention and management of obesity. In support of this concept, transgenic mice expressing the agouti gene specifically in adipocytes (a human-like pattern) respond to low calcium diets with accelerated weight gain and fat accretion, while high calcium diets markedly inhibit lipogenesis, accelerate lipolysis, increase thermogenesis and suppress fat accretion and weight gain in animals maintained at identical caloric intakes. Further, low calcium diets impede body fat loss, while high calcium diets markedly accelerate fat loss in transgenic mice subjected to caloric restriction. These findings are further supported by clinical and epidemiological data demonstrating a profound reduction in the odds of being obese associated with increasing dietary calcium intake. Notably, dairy sources of calcium exert a significantly greater anti-obesity effect than supplemental sources in each of these studies, possibly due to the effects of other bioactive compounds, such as the angiotensin converting enzyme inhibitor found in milk, on adipocyte metabolism, indicating an important role for dairy products in the control of obesity.