Urinary Excretion of Sodium, Nitrogen, and Sugar Amounts Are Valid Biomarkers of Dietary Sodium, Protein, and High Sugar Intake in Nonobese Adolescents

Abstract

Background: Objective indicators of dietary intake (e.g., biomarkers) are needed to overcome the limitations of self-reported dietary intake assessment methods in adolescents. To our knowledge, no controlled feeding studies to date have evaluated the validity of urinary sodium, nitrogen, or sugar excretion as dietary biomarkers in adolescents.Objective: This investigation aimed to evaluate the validity of urinary sodium, nitrogen, and total sugars (TS) excretion as biomarkers for sodium, protein, and added sugars (AS) intake in nonobese adolescents.Methods: In a crossover controlled feeding study design, 33 adolescents [12-18 y of age, 47 ± 25th percentile (mean ± SD) of body mass index (BMI; in kg/m2) for age] consumed 5% AS [low added sugars (LAS)] and 25% AS [high added sugars (HAS)] isocaloric, macronutrient-matched (55% carbohydrate, 30% fat, and 15% protein) diets for 7 d each, in a randomly assigned order, with a 4-wk washout period between diets. On the final 2 d of each diet period, 24-h urine samples were collected. Thirty-two adolescents completed all measurements (97% retention).Results: Urinary sodium was not different from the expected 90% recovery (mean ± SD: 88% ± 18%, P = 0.50). Urinary nitrogen was correlated with protein intake (r = 0.69, P < 0.001), although it was below the 80% expected recovery (62% ± 7%, P < 0.001). Urinary TS values were correlated with AS intake during the HAS diet (r = 0.77, P < 0.001) and had a higher R2 value of 0.28 than did AS intake (R2 = 0.36). TS excretion differed between LAS (0.226 ± 0.09 mg/d) and HAS (0.365 ± 0.16 mg/d) feeding periods (P < 0.001).Conclusions: Urinary sodium appears to be a valid biomarker for sodium intake in nonobese adolescents. Urinary nitrogen is associated with protein intake, but nitrogen excretion rates were less than previously reported for adults, possibly owing to adolescent growth rates. TS excretion reflects AS at 25% AS intake and was responsive to the change in AS intake. Thus, urinary biomarkers are promising objective indicators of dietary intake in adolescents, although larger-scale feeding trials are needed to confirm these findings. This trial was registered at clinicaltrials.gov as NCT02455388.

Keywords: adolescent dietary intake assessment; urinary nitrogen; urinary sodium; urinary sugars; dietary biomarkers.

Conflict of interest statement

Author disclosures: LBM, SVL, TMH, APN, VEH, and BMD, no conflicts of interest.

© 2017 American Society for Nutrition.

Figures

FIGURE 1

Study protocol for nonobese adolescents consuming low- and high-sugar diets. PAQ-A, Physical Activity Questionnaire for Adolescents; S, session.

FIGURE 2

Consolidated Standards of Reporting Trials diagram for nonobese adolescents consuming low- and high-sugar diets. Sequence A comprised a 5% AS diet in controlled feeding phase 1 and a 25% AS diet in phase 2. Sequence B comprised a 25% AS diet in controlled feeding phase 1 and a 5% AS diet in phase 2. AS, added sugars.

FIGURE 3

Association between urinary total sugar excretion and total sugars intake (A) and AS intake (B) in nonobese adolescents consuming low- and high-sugar diets. Each participant is denoted by a solid gray circle during the 5% AS diet and by a solid black circle during the 25% AS diet. The linear regression trendline is denoted by a solid black line, with dotted black lines indicating upper and lower 95% CIs. AS, added sugars.