A Diet High in Meat Protein and Potential Renal Acid Load Increases Absorption and Urinary Excretion of Calcium, As Well As Serum IGF-I in Postmenopausal Women

Objective: The objective was to determine the effect of increasing protein and potential renal acid load (PRAL) on Ca retention and markers of bone metabolism. Methods: In a randomized crossover design, twenty postmenopausal women consumed two diets: one low protein, low PRAL (LPLP) and one high protein (mostly meat), high PRAL (HPHP) for 7 wk each, separated by a one-week break. After 3 wk, the entire 2-d menu of each diet was radio-labeled with 47Ca and retention was measured by whole body scintillation counting for an additional 4 weeks. Biomarkers of bone metabolism in blood and urine were measured. Results: Compared with the LPLP diet, the HPHP diet increased urinary acidity (pH: 7.1 vs. 5.9, 0.25*, p < 0.01), urinary Ca excretion (156 vs. 203, 63 mg/d, p < 0.01), and blood IGF-I levels** [137 (103 184) vs. 174 (130 232) ng/ml, p < 0.01) consistently from week 1 through 7. The fractional Ca absorption was lower in subjects with LPLP than with HPHP diet (25.0 vs. 30.4, 5.4%, respectively, p < 0.02). The HPHP diet tended to increase the absolute amount of Ca absorbed compared with LPLP diet (227 vs. 258, 47 mg/d, p < 0.08). Conclusions: In postmenopausal women, a diet high in both meat protein and potential renal acid load increased serum IGF-I and Ca absorption, which was nearly equivalent to the increase in urinary excretion. A high meat diet does not appear detrimental for bone health. *Mean pooled SD; **Geometric means, ranges.