BIOAVAILABILITY OF CALCIUM IN YOGURT AND ITS RELATIONSHIP TO THE HYPOCHOLESTEROLEMIC PROPERTIES OF YOGURT

The objectives of this research were to determine the bioavailability of calcium in yogurt and its relationship to the hypocholesterolemic effects of yogurt. Three feeding trials were conducted using 21 day old Sprague Dawley male weanling rats as the animal model. The following calcium sources were evaluated: calcium carbonate, calcium carbonate with lactic acid added, unfermented yogurt, unfermented yogurt with lactic acid added, traditional yogurt, acidophilus yogurt, unfermented yogurt with hydrochloric acid added, or unfermented yogurt with citric acid added. Improved bone formation in response to dairy products occurred even though the diets were balanced for lactose. Fermented yogurt as well as unfermented yogurt with added lactic acid resulted in improved bone formation. Improved bone formation was not reflected in higher calcium or phosphorus bone levels but was a result of an alteration in bone matrix as measured by the response to stress. High dietary calcium resulted in an increased bone calcium and improved bone formation. The elastic properties of bone as demonstrated by the strain and modulus of elasticity measurements were affected by the level of dietary calcium. The physical properties of bone responded to level of dietary calcium, indicating that dietary calcium contributes to bone strength, but the bone responses were not dependent on the level of calcium in the bone. High dietary calcium played a role in reducing serum cholesterol and serum triglycerides. Additionally, the dietary source of calcium affected the response of serum triglycerides and cholesterol. The consumption of yogurt resulted in reduced serum cholesterol levels as compared to rats fed only calcium carbonate. The consumption of unfermented yogurt with added acid reduced serum cholesterol as compared to that of unfermented yogurt. However, the improved calcium bioavailability of the yogurt as measured by improved bone formation did not necessitate consistent serum lipid responses. The response of serum lipids to dietary calcium is dependent on the level of dietary calcium and on the source of the dietary calcium. If a dietary calcium source promotes bone formation, this does not preclude that it will reduce serum cholesterol and serum triglycerdies. (Abstract shortened with permission of author.