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A diet high in meat protein and potential renal acid load increases fractional Ca absorption and urinary Ca excretion, without affecting markers of bone resorption or formation in postmenopausal women

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Objective: The objective was to determine the effects of high dietary protein (mostly meat) and high potential renal acid load (PRAL) on calcium (Ca) balance and markers of bone metabolism. Methods: In a randomized crossover design, sixteen healthy postmenopausal women consumed two diets: one with low protein and low PRAL (LPLP; total protein: 61 g/d with meat protein: 12 g/d; PRAL: -48 mEq/d) and one with high protein (HPHP; total protein: 118 g/d with meat protein: 68g/d; PRAL: 33 mEq/d) for 7 wk each, separated by a one-wk break. After 3 wk dietary equilibration, the entire 2-d menu of each diet was radio-labeled with 47Ca and Ca absorption was measured by whole body scintillation counting for an additional 4 wk. Biomarkers of bone metabolism in blood and urine were measured. Results: Compared with the LPLP diet, the HPHP diet increased urinary acidity (mean ± pooled SD: pH 7.1 vs. 5.9 ± 0.2, p < 0.0001), urinary Ca excretion (156 vs. 203 ± 63 mg/d, p = 0.003), and blood IGF-I levels [geometric mean ± 1 pooled SD: 137 (114 – 164) vs. 175 (146 – 210) ng/ml, P < 0.0001], and decreased blood intact PTH levels [geometric mean ± 1 pooled SD: 59 (48 – 70) vs. 48 (40 – 57) ng/ml, P < 0.001] consistently throughout the study. In comparison to the LPLP diet, the HPHP diet increased subjects’ fractional Ca absorption (25.4 vs. 30.4 ± 5.4%, respectively, p < 0.02) and tended to increase the absolute amount of Ca absorbed (227 vs. 258 ± 47 mg/d, P < 0.08). The net difference between Ca absorbed and renal excretion was not significant between the LPLP and HPHP diets (82 vs. 59 ± 100 mg/d for the LPLP and the HPHP diets, respectively; P = 0.26). Conclusions: In healthy postmenopausal women, a diet high in both meat protein and potential renal acid load increased Ca absorption which counteracted the increase in urinary Ca excretion. The increased serum IGF-I combined with decreased serum PTH concentrations, with no change in biomarkers of bone resorption suggest a positive effect of a high protein diet on bone health. (This study was registered at number: NCT00620763.)
Jay J. Cao , LuAnn K. Johnson , Janet R. Hunt
USDA Scientist Submission
Journal of nutrition 2011 v.141
Journal Articles, USDA Authors, Peer-Reviewed
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