Calcium Retention of Young Adult Males as Affected by Level of Protein and of Calcium Intake*

The effect of protein intake (47, 95, and 142 g) on calcium retention, calcium absorption, and urinary calcium of 33 young adult males was determined at calcium intakes of 500, 800, and 1400 mg daily. Magnesium intake was 400 (27 subjects) or 490 mg (six subjects). The calcium‐to‐phosphorus ratio was 1.0 (1400 mg calcium intake), 0.8 (800 mg calcium intake), and 0.6 (500 mg calcium intake). When consuming the 47‐g protein intake, the subjects were consistently in calcium balance and the amount of calcium retained was unaffected by the calcium intake. At the 95‐g protein intake, none of the subjects were in calcium balance when 500 mg calcium was given, but they did achieve balance when 800 mg was given. When 142‐g protein was ingested, no subject was in balance at either the 500‐ or 800‐mg calcium intake and only three of 15 subjects were in balance at the 1400‐mg intake. Calcium absorption was not affected by dietary protein at an intake of 500 mg calcium, but significantly more calcium was absorbed at medium or high protein intakes than at low when 800 or 1400 mg calcium was given, the maximal protein effect having been reached at the 95‐g protein level. Urinary calcium was significantly affected by protein intake. All subjects, regardless of level of calcium intake, excreted less calcium when given the low protein diet than when given the medium, and all except two subjects excreted less when given the medium than when given the high protein diet.