Using Untargeted Metabolomics to Identify Urinary Biomarkers of Onion Intake

Fruit and vegetable (FV) intake has been reported as a modifiable risk factor of globally pervasive chronic diseases. Traditionally, the measurement of dietary intake has been conducted via self-report methods such as food diaries, food frequency questionnaires, and dietary recall. These methods are inherently subject to sources of error and biases. The objective measurement of diet-specific urinary biomarkers has been proposed as an alternate assessment method. A dose-dependent biomarker or biomarker panel for total FV intake has been investigated but not successfully established. In a recent publication as part of this PhD research, the researchers outlined a concise panel of 7 FVs that are predictive of total FV intake in a UK population. Recent studies have implemented an untargeted metabolomic approach to identify novel biomarkers of some of the 7 FVs identified in our prior research, but not with onion intake. The aim of this study is to detect, quantify and identify dose-dependent biomarker(s) of onion intake in a UK population using untargeted metabolomics. Phase 1 will be an acute randomised crossover intervention study, involving the consumption of a standardised portion of cooked onions (test) or couscous (control). Urine samples over the 24-hour period post-consumption will be collected. Phase 2 will be a dose-dependent crossover intervention study, where participants are supplied with supplementary onion portions (low, medium, high) to be consumed with their habitual evening meals. Within each supplementation period, participants will consume the same quantity of onions across the 4 days and collect a midstream first void urine samples on the fifth day. Trial order will be randomised, and a washout period of 3 days will be implemented between supplementation periods. 14 participants will be recruited for both phases of data collection. Urine samples will be analysed by high-performance liquid-chromatography with quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) to identify potential biomarkers.