Effect of high vegetable protein diets on urinary calcium loss in middle-aged men and women

Objective: To determine the effect of high-protein diets, which have recently been promoted for their health benefits, on urinary calcium losses and bone turnover in older subjects.Design: Randomized controlled cross-over study.Setting: Teaching hospital and university.Subjects: Twenty hyperlipidemic men and postmenopausal women (age 56 +/- 2 y) completed the study.Intervention: One-month test and control phases during which subjects consumed equi-energy metabolic diets high in calcium (11578 and 1593 mg/day, respectively). On the test diet 11 % of total dietary energy from starch in the control bread was replaced by protein (wheat gluten), resulting in 27% of energy from protein on the test diet vs 16% on the control diet.Main outcome measure: Urinary calcium excretion.Results: Compared with the control diet, at week 4, the test diet increased mean ( s.e.m.) 24 h urinary output of calcium (139 +/- 15 vs 227 +/- 21 mg, P = 0.004). The treatment difference in urinary calcium loss correlated with the serum anion gap as a marker of metabolic acid production (r=0.57, P=0.011). Serum calcium levels were marginally lower 2.41 +/- 0.02 vs 2.38 +/- 10.02mmol/l (P=0.075), but there was no significant treatment difference in calcium balance, possibly related to the high background calcium intake on both diets.Conclusion: In the presence of high dietary calcium intakes the vegetable protein gluten does not appear to have a negative effect on calcium balance despite increased urinary calcium loss.