Dietary Calcium and Body Fat: Cause and Effect

As dietary calcium intake increases, it acts at the cellular level to alter energy metabolism so that more food energy is burned and less is stored as fat. This is the conclusion of researchers at the University of Tennessee’s Department of Nutrition who studied the effect of dietary calcium levels in mice. 

The mice were genetically engineered to express a human obesity gene called “agouti” in their fat cells, making them useful models for the study of diet-induced obesity. The researchers, led by Michael B. Zemel, Ph.D., director of the University’s Nutrition Institute, found support for their conclusions in data from the third National Health and Nutrition Examination Survey (NHANES III), which shows an inverse relationship between calcium and dairy intakes and body fat in adults.  

Prior research from the Nutrition Institute shows that the agouti gene stimulates an increased flow of calcium into fat cells. This in turn liberates fatty acids and stimulates the activity of fatty acid synthase, an enzyme key to fat synthesis and storage (see related article on page 1). At the same time, calcium influx inhibits fat breakdown. The researchers suspected that hormones regulating calcium levels both within and outside of cells were key to these processes, and that dietary calcium could influence hormone activity. They went on to test the hypothesis that a low-calcium diet increases levels of circulating hormones, which in turn stimulate calcium influx into fat cells and increase fat synthesis and storage. They speculated that a high calcium diet could suppress hormonal activity and thereby reduce fat mass. 

The researchers placed four groups of mice on low-calcium (0.4 percent), high-fat, high-sucrose diets for 6 weeks. The basal group maintained the diet with no changes; a high calcium group received the diet supplemented with calcium carbonate to increase dietary calcium to 1.2 percent; a medium dairy group received 25 percent of its protein as non-fat dry milk with dietary calcium at 1.2 percent; and a high dairy group received 50 percent of its protein from non-fat dry milk with a dietary calcium level of 2.4 percent. After 6 weeks, the basal diet group experienced a weight gain of 24 percent. The high calcium group gained about 18 percent; the medium dairy group, 17 percent; and the high dairy group, less than 15 percent. These differences occurred despite all groups consuming the same quantity of food.  

The researchers concluded that low calcium diets lead to increased fat storage and higher calcium diets favor increased burning of fat. Dietary calcium in the form of dairy had an even greater effect on reducing fat storage than a calcium supplement. The authors propose that calcium in fat cells “is a logical target for pharmacological and/or nutritional regulation” of  overweight and obesity.