Screening Performance for Insufficient Vegetable Intake in Young Adult Japanese Women: Spot Urinary Potassium Excretion as a Simple, Non-Invasive Marker

<b>Background/Objectives:</b> Existing methods for assessing the intake of vegetables and fruits have limitations. This study aims to investigate the number of measurements required to screen individuals with insufficient usual vegetable intake or total fruit and vegetable intake using urinary potassium excretion estimated from spot urine samples, a non-invasive and simple biomarker. <b>Methods:</b> A total of 97 women aged 18-24 years provided a 12-day dietary survey, four 24 h urine collections, and three timed spot urine samples per day, collected in a duration of 4 days. Using the dietary surveys as a reference, we evaluated the number of spot urine samples required and their screening performance for identifying individuals whose vegetable intake or total fruit and vegetable intake was below the study population mean. Screening performance was assessed by receiver operating characteristic analysis and the area under the curve (AUC). <b>Results:</b> For vegetable intake, the AUCs were >0.70 when either a single spot urine sample was collected at the second urine void after waking or ≥2 spot urine samples were collected at arbitrary time points. For total fruit and vegetable intake, AUCs were >0.70 when using a single spot urine sample collected at the second void after waking up. <b>Conclusions:</b> These findings suggest that a time-specific single spot urine sample (i.e., the second urine void after waking) or ≥2 spot urine samples collected at arbitrary time points may help in screening individuals with habitually insufficient vegetable intake.