A study by Massachusetts General Hospital endocrinologists found that ingesting the U.S. recommended dietary allowance of protein reduces urinary calcium excretion and bone resorption in premenopausal women.
"High-protein diets increase calciuria. No previous studies have examined the ad libitum U.S. diet's effect on calciuria or bone resorption," stated B.A. Ince and colleagues.
"Thirty-nine healthy, premenopausal women consuming ad libitum diets (mean, 1.1g/kg protein, 819mg (20.5mmol) Ca, 1152mg (37mmol) P, 129mmol Na) were switched to isocaloric diets containing the U.S. recommended dietary allowance (RDA) of protein (0.8g/kg) and similar amounts of calcium, phosphorus and sodium. Bone resorption and related endpoints were assessed before and one week after the switch," the researchers reported.
They found that "(a)s dietary protein changed from ad libitum to RDA levels, mean urine nitrogen decreased 26% (2.4g/d; p<0.001), and mean blood urea nitrogen decreased 15% (1.9mg/dl; p<0.001). Mean urine pH increased from 6.3 to 6.8 (p<0.001), and net renal acid excretion (NRAE = urine ammonium plus titratable acids minus bicarbonate) decreased 68% (21.4mEq/d; p<0.001)."
"Mean urinary calcium decreased 32% (42mg (1mmol)/d; p<0.001), and bone resorption urine N-telopeptides) decreased 17% (74 micromol bovine collagen equivalents/d; p<0.001).
"Mean serum calcium, PTH and 1,25 dihydroxy vitamin D remained unchanged," Ince's team said.
"In this two-week study, decreasing dietary protein from ad libitum to RDA levels decreased NRAE, calciuria and estimates of bone resorption, suggesting that decreased U.S. protein consumption might reduce bone loss.
"Inasmuch as other dietary modifications, such as increasing vegetable and fruit intake, can result in sustained reductions in NRAE without reducing protein intake, the advisability of reducing protein intake for skeletal protection from acid attack requires further investigation," the endocrinologists concluded.
Ince and coauthors published their study in the Journal of Clinical Endocrinology and Metabolism ("Lowering dietary protein to U.S. recommended dietary allowance levels reduces urinary calcium excretion and bone resorption in young women." J Clin Endocrinol Metab, 2004;89(8):3801-3807).
For more information, contact B.A. Ince, Massachusetts General Hospital, Division Endocrine, Bulfinch 327, 55 Fruit St., Boston, MA 02114 USA.