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Title:The Effect of Long Term High Protein Induced Calciuria on Calcium Metabolism and Bone Status in Adult Rats
Author(s):Calvo, Mona Schiess
Department / Program:Food Science
Discipline:Food Science
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Health Sciences, Nutrition
Abstract:The marked calciuria which occurs during high protein consumption in humans and rats has been implicated as a factor in the etiology of osteoporosis. The source of increased urinary calcium is controversial and has been attributed to either increased absorption, increased bone resorption or both. A 20 week study was conducted to determine long-term effects of various protein sources on calcium metabolism and bone status of 500 g male rats "deep-labelled" with ('45)Ca. Controls were fed diets containing 6% protein as casein and compared to rats fed diets containing 6% casein plus 24% protein as either lactalbumin, beef, casein, soy, egg white or gelatin. Diets supplied all essential nutrients with Mg, P and Ca held constant (0.18, 0.4 and 0.6%, respectively). Protein sources differed in their ability to produce calciuria. Urinary ('45)Ca excretion was greater (P < 0.001) for rats fed lactalbumin, egg white and gelatin diets. The ('40)Ca and ('45)Ca data indicate that the calciuric effect of high protein consumption in adult rats is transient. Long-term consumption of high protein diets did not stimulate increased bone resorption or alter bone mineral composition indicating that bone in not the source of calcium excretion during long term protein-induced calciuria in the rat.
A second 20-week study investigated the effects of excess dietary protein when calcium intake was inadequate. Control rats were fed 10% protein as casein and protein was increased to moderate (25%) or high (40%) levels by the addition of both egg white and beef. Each level of protein was fed at a calcium adequate (0.6%) and inadequate (0.05%) intake. Increasing dietary protein induced a mild transient calciuria but did not exacerbate bone resorption or alter bone composition when calcium intake was either adequate or inadequate.
Analyses of 24 hour urine collected periodically during the 20 week studies gave some insight into possible mechanisms through which high protein consumption may induce calciuria. Previous studies have determined that increases in the urinary excretion of calcium chelating anions impede the renal tubular resorption of calcium thus causing more to be excreted in the urine. The consumption of those test protein diets which induced marked calciuria (lactalbumin, egg white and gelatin) also produce significantly high levels of urinary sulfate and, in the case of gelatin, urinary oxalate. Both anions formed by the catabolism of excess sulfur amino acids and glycine, respectively, may be factors involved in the calciuric effect of high protein diets. Additionally, egg white consumption was associated with high levels of urinary sodium, a cation repeatedly shown to competitively interfere with the renal distal tubular reabsorption of calcium. These findings indicate that various protein diets may induce calciuria via different mechanisms or some combination of these.
Issue Date:1980
Description:177 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
Other Identifier(s):(UMI)AAI8108457
Date Available in IDEALS:2015-05-13
Date Deposited:1980

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