Calcium absorption from dairy products, vegetables, and legumes in premenopausal women
Abstract
Fractional absorption of calcium from dairy products was measured using a stable nonradioactive isotope, $\sp{44}$Ca, as a tracer in healthy premenopausal women. Cheddar cheese, processed cheese, and yogurt were prepared from milk intrinsically labeled with $\sp{44}$Ca. $\sp{44}$Ca labeled tribasic calcium phosphate ($\rm\sp{44}Ca\sb{10}(OH)\sb2(PO\sb4)\sb6)$ was incorporated into a cheese analogue. As a referent $\sp{44}$Ca labeled milk was used. Subjects were given a controlled diet for 4 days at the early follicular phase of their menstrual cycle. Each labeled dairy product was tested in a randomized order as part of a controlled diet in 7 subjects. Fecal samples were collected for the analysis of total calcium and isotopic abundance of the tracer. Absorption of calcium was similar for all dairy products tested averaging 31.2%. Thus, calcium fractional absorption by premenopausal women was not affected by the lactose content, fermentation, or the chemical form of the calcium in a variety of dairy products. When vegetables labeled with a radioactive $\sp{45}$Ca by hydroponic growing were tested in premenopausal women, high oxalate containing rhubarb exhibited lower calcium absorption than low oxalate-containing sweet potatoes. However, rhubarb whose oxalate content and oxalate: calcium molar ratio are higher than those of spinach showed better absorption of calcium. The absorption of calcium from spinach was lower than that of synthetic calcium oxalate salt, indicating other factors such as size of calcium oxalate crystals in vegetables may offset the antiabsorptive effect of oxalate in spinach. Dry beans showed reduced calcium absorption due to the presence of phytate and oxalate. However, in soybeans, the presence of high levels of phytate and oxalate did not reduce calcium absorption as much as dry beans. Phytate and oxalate in foods generally inhibit absorption of food calcium, but the extent of their interference varies from food to food, even when they are present in stoichiometric excess.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Nutrition|Anatomy & physiology|Animals
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