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* Department of Allied Health, University of Connecticut, Storrs, CT;
Yale University, School of Internal Medicine, New Haven, CT; ** Division of Nutritional Sciences, Cornell University, Ithaca, NY; and
Yale New Haven Hospital, New Haven, CT
3 To whom correspondence should be addressed. E-mail: jane.kerstetter{at}uconn.edu.
We showed that increasing dietary protein from omnivorous sources increases intestinal calcium absorption and urinary calcium, whereas a low-protein diet decreases calcium absorption and lowers urinary calcium. To assess the effect of soy protein on this relation, we substituted soy for meat in high- and low-protein diets fed to healthy women. The study consisted of a 2-wk adjustment period followed by a 4-d experimental period in which 20 healthy women consumed, in random order, the following 4 diets: high-protein soy-based, low-protein soy-based, high-protein meat-based, low-protein meat-based. Measures of calcium homeostasis were evaluated at baseline and after 4 d of the experimental period. At 24 h, net acid excretion was higher during the high- compared with the low-protein intervention (P < 0.05), and during the meat compared with the soy intervention (P < 0.05). The high-protein diets increased 24-h urinary calcium (P < 0.001), but urinary calcium did not differ due to the type of protein. Serum concentrations of parathyroid hormone and calcitriol, and urinary nephrogenous cAMP were higher during the low- compared with the high-protein intervention and during the soy compared with the meat protein (P < 0.05). In a subset of subjects, intestinal calcium absorption tended to be lower (P = 0.1) when they consumed the soy diets rather than the meat diets. These data indicate that when soy protein is substituted for meat protein, there is an acute decline in dietary calcium bioavailability.
KEY WORDS: dietary protein calcium metabolism soy meat parathyroid hormone
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