Dietary protein and calcium interact to influence calcium retention: a controlled feeding study.
BACKGROUND
The effect of meat protein on calcium retention at different calcium intakes is unresolved.


OBJECTIVE
The objective was to test the effect of dietary protein on calcium retention at low and high intakes of calcium.


METHODS
In a randomized controlled feeding study with a 2 x 2 factorial crossover design, healthy postmenopausal women (n = 27) consumed either approximately 675 or approximately 1510 mg Ca/d, with both low and high protein (providing 10% and 20% energy) for 7 wk each, separated by a 3-wk washout period. After 3 wk, the entire diet was extrinsically labeled with (47)Ca, and isotope retention was monitored by whole-body scintillation counting. Clinical markers of calcium and bone metabolism were measured.


RESULTS
High compared with low dietary protein significantly increased calcium retention from the low-calcium (29.5% compared with 26.0% absorbed) but not the high-calcium diet (18% absorbed). For the low-calcium diet, this effect nearly balanced a protein-related 0.5-mmol/d greater urinary calcium excretion. Protein-related calciuretic effects were independent of dietary calcium. Testing at 1, 2, 3, 5, and 7 wk showed no long-term adaptation in urinary acidity or urinary calcium excretion. High compared with low dietary protein decreased urinary deoxypyridinoline and increased serum insulin-like growth factor I without affecting parathyroid hormone, osteocalcin, bone-specific alkaline phosphatase, or tartrate-resistant acid phosphatase.


CONCLUSIONS
In healthy postmenopausal women, a moderate increase in dietary protein, from 10% to 20% of energy, slightly improved calcium absorption from a low-calcium diet, nearly compensating for a slight increase in urinary calcium excretion. Under practical dietary conditions, increased dietary protein from animal sources was not detrimental to calcium balance or short-term indicators of bone health.
Hunt
Janet R
JR
US Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND, USA. janetrhunt@gmail.com
Johnson
Luann K
LK
Fariba Roughead
Z K
ZK
D000368:Aged; D000369:Aged, 80 and over; D000641:Ammonia / Q000652:urine; D015992:Body Mass Index; D002118:Calcium / Q000097:blood* / Q000652:urine; D002132:Calcium Radioisotopes; D002136:Calcium, Dietary / Q000494:pharmacology*; D018592:Cross-Over Studies; D018753:Diet, Protein-Restricted; D004044:Dietary Proteins / Q000494:pharmacology*; D002149:Energy Intake; D005260:Female; D006801:Humans; D008875:Middle Aged; D017698:Postmenopause
D002132:Calcium Radioisotopes; D002136:Calcium, Dietary; D004044:Dietary Proteins; D000641:Ammonia; D002118:Calcium