ResearchComparison of estimated renal net acid excretion from dietary intake and body size with urine pH☆,☆☆
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Subjects and study procedures
The Observing Protein and Energy Nutrition (OPEN) study was designed to assess the structure of measurement error in dietary instruments (FFQ and 24-hour dietary recalls) with biomarkers of nutrient intake, namely doubly labeled water for energy expenditure, urinary nitrogen, sodium, and potassium. For this study, volunteers were recruited from the suburban Maryland metropolitan area of Washington, DC. A random sample of 5,000 households with telephone numbers listed in the white pages and with
Results
The majority of participants in this study were white, well educated (with at least some college education), and never smokers (Table 1).
Characteristic % Gender Male 53.9 Female 46.1 Education level Less than high school 1.7 High school 11.6 Some college 22.7 College graduate 31.2 Postgraduate 31.6 Race White 84.9 African American 6.2 Asian 5.4 Other/refused 3.5 Smoking status Never 58.4 Past 30.9 Current 10.8
Discussion
Results from this study indicate that urine pH can be estimated indirectly from dietary data and body size. Among 440 healthy volunteers, we observed a correlation of −0.40 between urine pH and estimated NAE when using FFQs or 24-hour recalls, and these correlations increased to −0.50 after correcting for intraperson variation in urine pH levels.
It has been known for almost a decade that dietary intake can affect the acidity of urine (5). However, until the publication by Remer and Manz (6),
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2009, Nutrition ResearchCitation Excerpt :Studies of urine pH have revealed that urine pH from less than 24-hour samples is correlated with food intake as measured in both food record and food frequency questionnaires [15] and with fruit, vegetable, and meat but not with dairy or cereal foods intakes [16], bone mineral density in children [20], and changes in type of mineral water consumed [17]. Most analyses of urine acid load excretion have been based on 24-hour urine collections; however, less than 24-hour samples have also shown utility for estimating the dietary acid-alkaline load status [12-15]. Collection of fasting morning urine has a lower subject burden compared to 24-hour collections, and if this single sample reflects dietary intakes, it could be a useful tool for future nutrition surveys.
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Address correspondence to: Dominique S. Michaud, ScD, National Cancer Institute, 6120 Executive Blvd, EPS/320 MSC 7232, Bethesda, MD 20892-7232. E-mail: [email protected]
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0002-8223/03/10308-0005$35.00/0