title: Dietary protein-induced increases in urinary calcium are accompanied by similar increases in urinary nitrogen and urinary urea: a controlled clinical trial.
abstract: To determine the usefulness of urinary urea as an index of dietary protein intake, 10 postmenopausal women were enrolled in and completed a randomized, double-blind, cross-over feeding trial from September 2008 to May 2010 that compared 10 days of a 45-g whey supplement with 10 days of a 45-g maltodextrin control. Urinary nitrogen, urinary calcium, urinary urea, and bone turnover markers were measured at days 0, 7, and 10. Paired sample t tests, Pearson's correlation statistic, and simple linear regression were used to assess differences between treatments and associations among urinary metabolites. Urinary nitrogen/urinary creatinine rose from 12.3±1.7 g/g (99.6±13.8 mmol/mmol) to 16.8±2.2 g/g (135.5±17.8 mmol/mmol) with whey supplementation, but did not change with maltodextrin. Whey supplementation caused urinary calcium to rise by 4.76±1.84 mg (1.19±0.46 mmol) without a change in bone turnover markers. Because our goal was to estimate protein intake from urinary nitrogen/urinary creatinine, we used our data to develop the following equation: protein intake (g/day)=71.221+1.719×(urinary nitrogen, g)/creatinine, g) (R=0.46, R(2)=0.21). As a more rapid and less costly alternative to urinary nitrogen/urinary creatinine, we next determined whether urinary urea could predict protein intake and found that protein intake (g/day)=63.844+1.11×(urinary urea, g/creatinine, g) (R=0.58, R(2)=0.34). These data indicate that urinary urea/urinary creatinine is at least as good a marker of dietary protein intake as urinary nitrogen and is easier to quantitate in nutrition intervention trials.
authors: Jessica D
authors: JD
authors: Bihuniak
authors: Christine A
authors: CA
authors: Simpson
authors: Rebecca R
authors: RR
authors: Sullivan
authors: Donna M
authors: DM
authors: Caseria
authors: Jane E
authors: JE
authors: Kerstetter
authors: Karl L
authors: KL
authors: Insogna
mesh_terms: D015415:Biomarkers / Q000652:urine*; D001842:Bone and Bones / Q000378:metabolism; D002118:Calcium / Q000652:urine*; D003404:Creatinine / Q000652:urine; D018592:Cross-Over Studies; D004044:Dietary Proteins / Q000008:administration & dosage / Q000493:pharmacokinetics*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008875:Middle Aged; D008894:Milk Proteins / Q000008:administration & dosage / Q000493:pharmacokinetics; D009584:Nitrogen / Q000652:urine*; D011134:Polysaccharides / Q000008:administration & dosage / Q000493:pharmacokinetics; D017698:Postmenopause; D014508:Urea / Q000652:urine*; D000067816:Whey Proteins
chemical_list: D015415:Biomarkers; D004044:Dietary Proteins; D008894:Milk Proteins; D011134:Polysaccharides; D000067816:Whey Proteins; C008315:maltodextrin; D014508:Urea; D003404:Creatinine; D009584:Nitrogen; D002118:Calcium