A threshold for low-protein-diet-induced elevations in parathyroid hormone.
BACKGROUND
We reported previously that lowering dietary protein intake in young healthy women to 0.7 g/kg depressed intestinal calcium absorption and was accompanied by elevations in parathyroid hormone (PTH). Moderate amounts of dietary protein (1.0 g/kg) did not appear to perturb calcium homeostasis.


OBJECTIVE
The purpose of this study was to evaluate the effect of graded intakes of dietary protein (0.7, 0.8, 0.9, and 1.0 g/kg) on calcium homeostasis.


METHODS
The experiment consisted of 2 wk of a well-balanced diet containing moderate amounts of calcium, sodium, and protein followed by 4 d of an experimental diet containing 1 of 4 amounts of protein. Eight young healthy women received the 4 amounts of protein in random order. The average age of the subjects was 23.1 +/- 2.3 y, their weight was 64 +/- 3 kg, and their body mass index (in kg/m(2)) was 24.3 +/- 0.9.


RESULTS
Elevations in PTH developed by day 4 of the diets containing 0.7 and 0.8 g protein/kg but not during the diets containing 0.9 or 1.0 g protein/kg. By day 4 of the 0.7- and 0. 8-g/kg diets, midmolecule PTH, calcitriol, and nephrogenous cyclic adenosine monophosphate were 1.5-3.5-fold higher than on day 0. Calcitropic hormones on day 4 of the diets containing 0.8 and 0.9 g protein/kg were within the normal range and 23-57% lower than values observed with the 0.7- and 0.8-g/kg diets (P < 0.005). Mean 24-h urinary calcium was 3.29 +/- 0.35 mmol with the diet containing 0.7 g protein/kg and 3.54 +/- 0.46 mmol with the diet containing 1.0 g protein/kg.


CONCLUSIONS
Our data suggest that in young healthy women consuming a well-balanced diet, the current recommended dietary allowance for protein (0.8 g/kg) results in short-term perturbations in calcium homeostasis.
Kerstetter
J E
JE
School of Allied Health, University of Connecticut, Storrs, CT 06269-2101, USA. jane.kerstetter@uconn.edu
Svastisalee
C M
CM
Caseria
D M
DM
Mitnick
M E
ME
Insogna
K L
KL
D000328:Adult; D002118:Calcium / Q000097:blood / Q000378:metabolism* / Q000652:urine; D018753:Diet, Protein-Restricted; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D006706:Homeostasis; D006801:Humans; D007408:Intestinal Absorption; D009751:Nutritional Requirements; D010281:Parathyroid Hormone / Q000097:blood*
D004044:Dietary Proteins; D010281:Parathyroid Hormone; D002118:Calcium