***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: 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 grade d intakes of dietary protein ( 0.7 , 0.8 , 0.9 , and 1.0 g/kg ) on calcium homeostasis . DESIGN 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 r and om 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 BACKGROUND The metabolic effects of diets high in vegetable protein have not been assessed despite much recent interest in the effect of soy proteins in reducing serum cholesterol . OBJECTIVE We assessed the metabolic effects of diets high in vegetable protein ( specifically , wheat gluten ) on serum lipids , uric acid concentrations , and renal function . DESIGN Twenty hyperlipidemic men and women consumed isoenergetic test ( high-protein ) and control metabolic diets for 1 mo in a r and omized crossover design . In the high-protein diet , 11 % of the total dietary energy from starch in the control bread was replaced by vegetable protein ( wheat gluten ) , result ing in 27 % of total energy from protein compared with 16 % in the control diet . In other respects , the 2 diets were identical . RESULTS Compared with the control , the high-protein diet result ed in lower serum concentrations of triacylglycerol ( by 19.2 + /- 5.6 % ; P = 0.003 ) , uric acid ( by 12.7 + /- 2.0 % ; P < 0.001 ) , and creatinine ( by 2.5 + /- 1.1 % ; P = 0.035 ) and higher serum concentrations of urea ( by 42.2 + /- 5.8 % ; P < 0.001 ) and a higher 24-h urinary urea output ( by 99.2 + /- 17.2 % ; P < 0.001 ) . No significant differences were detected in total or HDL cholesterol or in the renal clearance of creatinine . LDL oxidation , assessed as the ratio of conjugated dienes to LDL cholesterol in the LDL fraction , was lower with the high-protein diet ( by 10.6 + /- 3.6 % ; P = 0.009 ) . CONCLUSIONS High intakes of vegetable protein from gluten may have beneficial effects on cardiovascular disease risk by reducing oxidized LDL , serum triacylglycerol , and uric acid . Further studies are required to assess the longer-term effects on renal function Increasing dietary protein induces hypercalciuria and a negative calcium balance . Despite this , the influence of dietary protein on the parathyroid hormone ( PTH ) I-a-hydroxylase axis is not well understood . We therefore examined the effect of three amounts of dietary protein : low ( 0.7 g/kg ) , medium ( 1.0 g/kg ) , and high ( 2.1 g/kg ) on mineral metabolism and the PTH-1-alpha-hydroxylase axis in 16 healthy women aged 26.7 + /- 1.3 y. By day 4 , urinary calcium decreased significantly with the low-protein diet and increased significantly with the high-protein diet compared with the medium-protein diet ( control ) . Also by day 4 , there were striking elevations in serum PTH and calcitriol [ 1,25-dihydroxyvitamin D ] in subjects consuming the low-protein diet .  Serum PTH , by two different assays , was 1.5 - 2.4 times higher and by day 14 1.6 - 2.7 times higher during the low-protein diet compared with the medium-protein diet . This was accompanied by a significant increase in both nephrogenous cyclic adenosine monophosphate ( cAMP ) , a sensitive and specific indicator of PTH bioactivity , and serum calcitriol by day 14 . In comparison , there were relatively minor changes in the calcitropic hormones with the medium- and high-protein diets . The stimulus for the elevation in PTH induced by protein restriction is unclear , but probably does not involve a simple renal mechanism and could reflect either a decline in intestinal calcium absorption , a reduction of bone turn-over , or both . Our data indicate that dietary protein is a powerful regulator of calcium metabolism . Further study is needed to both clarify the mechanisms by which these changes are induced and to better define the amount of dietary protein that will optimize skeletal health in young women We showed that increasing dietary protein from omnivorous sources increases intestinal calcium absorption and urinary calcium , whereas a low-protein diet decreases calcium absorption and lowers urinary calcium . To assess the effect of soy protein on this relation , we substituted soy for meat in high- and low-protein diets fed to healthy women . The study consisted of a 2-wk adjustment period followed by a 4-d experimental period in which 20 healthy women consumed , in r and om order , the following 4 diets : high-protein soy-based , low-protein soy-based , high-protein meat-based , low-protein meat-based . Measures of calcium homeostasis were evaluated at baseline and after 4 d of the experimental period . At 24 h , net acid excretion was higher during the high- compared with the low-protein intervention ( P < 0.05 ) , and during the meat compared with the soy intervention ( P < 0.05 ) . The high-protein diets increased 24-h urinary calcium ( P < 0.001 ) , but urinary calcium did not differ due to the type of protein . Serum concentrations of parathyroid hormone and calcitriol , and urinary nephrogenous cAMP were higher during the low- compared with the high-protein intervention and during the soy compared with the meat protein ( P < 0.05 ) . In a subset of subjects , intestinal calcium absorption tended to be lower ( P = 0.1 ) when they consumed the soy diets rather than the meat diets . These data indicate that when soy protein is substituted for meat protein , there is an acute decline in dietary calcium bioavailability Calcium balance is decreased by an increased intake of purified proteins , although the effects of common dietary sources of protein ( like meat ) on calcium economy remain controversial . We compared the effects of several weeks of controlled high and low meat diets on body calcium retention , using sensitive radiotracer and whole body scintillation counting methodology . Healthy postmenopausal women ( n = 15 ) consumed diets with similar calcium content ( approximately 600 mg ) , but either low or high in meat ( 12 vs. 20 % of energy as protein ) for 8 wk each , in a r and omized crossover design . After 4 wk of equilibration of each diet , calcium retention was measured by extrinsically labeling the 2-d menu with (47)Ca , followed by whole body scintillation counting for 28 d. Urinary and blood indicators of bone metabolism were also determined for each diet . Calcium retention was not different during the high and low meat dietary periods ( d 28 , mean + /- pooled SD : 17.1 and 15.6 % , + /-0.6 % , respectively ; P = 0.09 ) . An initially higher renal acid excretion in subjects consuming the high meat compared with the low meat diet decreased significantly with time . The diets did not affect urinary calcium loss or indicators of bone metabolism . In conclusion , under controlled conditions , a high meat compared with a low meat diet for 8 wk did not affect calcium retention or biomarkers of bone metabolism in healthy postmenopausal women .  Calcium retention is not reduced when subjects consume a high protein diet from common dietary sources such as meat BACKGROUND Changes in dietary protein in adults are associated with changes in urinary calcium excretion . The mechanisms underlying this effect are not completely understood , but alterations in intestinal absorption of calcium are not thought to be involved . OBJECTIVE We reexamined this mechanism by evaluating the effect of 2 amounts of dietary protein ( low : 0.7 g/kg ; and high : 2.1 g/kg ) on fractional calcium absorption in 7 healthy , young women . DESIGN The experiment consisted of 2 wk of a well-balanced diet containing moderate amounts of calcium , sodium , and protein followed by 5 d of an experimental diet that contained 1 of 2 amounts of protein and constant amounts of other nutrients known to influence calcium metabolism . Seven subjects received both amounts of dietary protein in r and om order . Blood and urine were sample d at baseline and on day 4 . Fractional calcium absorption was measured by dual-stable calcium isotopes on day 5 . In a second study of 5 additional women , we evaluated the effects of dietary fiber on calcitropic hormones . RESULTS Subjects developed hypocalciuria and secondary hyperparathyroidism on day 4 of the low-protein diet .  Urinary calcium excretion and the glomerular filtration rate were elevated significantly by day 4 of the high-protein compared with the low-protein diet .  Fractional calcium absorption after the low-protein diet was 0.19+/-0.03 , which was significantly lower than that after the high-protein diet ( 0.26+/-0.03 , P=0.05 ) . CONCLUSION These data provide evidence that depressed intestinal calcium absorption explains , in part , low-protein-induced secondary hyperparathyroidism Objective : To determine the effect of high-protein diets , which have recently been promoted for their health benefits , on urinary calcium losses and bone turnover in older subjects . Design : R and omized controlled cross-over study . Setting : Teaching hospital and university . Subjects : Twenty hyperlipidemic men and postmenopausal women ( age 56±2 y ) completed the study . Interventions : One-month test and control phases during which subjects consumed equi-energy metabolic diets high in calcium ( 1578 and 1593 mg/day , respectively ) . On the test diet 11 % of total dietary energy from starch in the control bread was replaced by protein ( wheat gluten ) , result ing in 27 % of energy from protein on the test diet vs 16 % on the control diet . Main outcome measure : Urinary calcium excretion . Results : Compared with the control diet , at week 4 , the test diet increased mean ( ±s.e.m . ) 24 h urinary output of calcium ( 139±15 vs 227±21 mg , P=0.004 ) . The treatment difference in urinary calcium loss correlated with the serum anion gap as a marker of metabolic acid production ( r=0.57 , P=0.011 ) . Serum calcium levels were marginally lower 2.41±0.02 vs 2.38±0.02 mmol/l ( P=0.075 ) , but there was no significant treatment difference in calcium balance , possibly related to the high background calcium intake on both diets . Conclusions : In the presence of high dietary calcium intakes the vegetable protein gluten does not appear to have a negative effect on calcium balance despite increased urinary calcium loss . Sponsorship : The University-Industry Research Partnership Program of the Natural Sciences and Engineering Research Council of Canada , Loblaw Br and s Limited , Toronto , ON , and Kraft Canada Inc. Don Mills , ON . DJAJ is funded as a Canada Research Chair in Metabolism and Nutrition at the University of Toronto by the Federal Government of Canada , Ottawa Decline in muscle mass , protein synthesis , and mitochondrial function occurs with age , and amino acids are 
    Output:
    
The evidence from the current review is limited and inconsistent with regard to the role of protein intake and the risk of kidney stones .
Increased protein intake had little or no effect on blood markers of kidney function .
Evidence reported here suggests that protein intake above the US RDA has no adverse effect on blood pressure .
These data further indicate that , at least in the short term , higher protein intake within the range of recommended intakes for protein is consistent with normal kidney function in healthy individuals