Does anyone agree with this? However scientists still do not understand how calcium promotes fat reduction. Michael Zemel, a nutritionist at the University of Tennessee, suggests that it has to do with the actions of vitamin D. Data appear to show that the active form of vitamin D, called calcitriol, causes fat cells to create more fat. Calcitriol levels are raised with lower intake of calcium. Therefore, fat cells produce more fat on low calcium diets. By contrast, high-calcium diets suppress calcitriol and, as a consequence, promote the burning of fat.