Research
Comparison of estimated renal net acid excretion from dietary intake and body size with urine pH,☆☆

https://doi.org/10.1016/S0002-8223(03)00469-3Get rights and content

Abstract

Objective The aim of this study was to examine whether estimated net acid excretion (NAE) from two dietary assessment instruments can predict urine pH in healthy volunteers. Design The Observing Protein and Energy Nutrition (OPEN) study, which was designed to assess dietary measurement error, included men and women aged 40 to 69 years. Participants were asked to complete two food frequency questionnaires (FFQs) and two 24-hour recalls at approximately three-month intervals, and to return two 24-hour urine samples during the same period. NAE was estimated using a previously described equation. The estimates obtained from the different dietary assessment measures were correlated with actual urine pH. Subjects/Setting Four hundred eighty-four subjects were enrolled in the OPEN study. All participants were included in this study on urine pH, given that they had all completed at least one dietary assessment and one urine sample. The study took place in Montgomery County, MD, between September 1999 and March 2000. Results Correlation coefficients between NAE estimates using the FFQ data and the average of two urine pH measures were −0.34 and −0.39 for women and men, respectively. Removing within-person variance in the urine pH levels resulted in a deattenuated overall correlation of −0.50 for the FFQ. Correlations between the 24-hour recall estimates of NAE were −0.41 and −0.32 for women and men, respectively. For the 24-hour recalls, the deattenuated overall correlation was −0.50. Application/Conclusions Our findings suggest that FFQs provide adequate dietary data to estimate renal NAE and could be used as a surrogate for urinary pH levels in large epidemiologic studies. J Am Diet Assoc. 2003;103:1001-1007.

Section snippets

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).

. Baseline characteristics of persons who participated in the Observing Protein and Energy Nutrition study (N=484)

Characteristic%
Gender
Male53.9
Female46.1
Education level
Less than high school1.7
High school11.6
Some college22.7
College graduate31.2
Postgraduate31.6
Race
White84.9
African American6.2
Asian5.4
Other/refused3.5
Smoking status
Never58.4
Past30.9
Current10.8
The

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),

References (19)

There are more references available in the full text version of this article.

Cited by (35)

  • Long-term dietary acid load is associated with depression in multiple sclerosis, but less evidence was found with fatigue and anxiety

    2023, Multiple Sclerosis and Related Disorders
    Citation Excerpt :

    To assess dietary acid load, we derived two indices from the dietary intake data, the PRAL and the NEAP. Both measures have been validated and have been shown to reflect a long-term diet acid intake (Remer and Manz, 1995; Michaud et al., 2003; Scialla and Anderson, 2013). Higher values of the PRAL and NEAP reflect more acidic dietary intake, whereas lower values indicate more alkaline dietary intake.

  • Dietary acid load, metabolic acidosis and insulin resistance – Lessons from cross-sectional and overfeeding studies in humans

    2016, Clinical Nutrition
    Citation Excerpt :

    Plasma lactate and the dietary acid load scores PRAL and NEAP did not correlate at baseline or with overfeeding in the present study. In contrast, other studies that measured RNAE in 238 children and adolescents [34] or RNAE and urinary pH in 482 adults [35] have demonstrated significant associations between these direct measures of body acid/base balance and dietary acid load. Notably, the smaller sample size and the use of plasma lactate as an indicator of body acidity may have limited the power to detect these associations in the present study.

  • Increasing fruits and vegetables in midlife women: A feasibility study

    2013, Nutrition Research
    Citation Excerpt :

    The lower-acid/dietary approaches to stopping hypertension-type diet achieved an estimated NEAP reduction of −7.1mEq/d [60]. Urine pH is an indirect measure of net acid excretion [48-50] and was expected to show an increase over time owing to the decreased dietary NEAP [57]. An important finding from this study was the significant increase achieved in urine pH. Women reported that daily use of the pH dipsticks to self-monitor their urine pH helped motivate them to increase fruit and vegetable intake.

  • Low 5-year stability of within-patient ion excretion and urine pH in fasting-morning-urine specimens

    2009, Nutrition Research
    Citation 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.

View all citing articles on Scopus

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]

☆☆

0002-8223/03/10308-0005$35.00/0

View full text