Participants will report to the laboratory at 8am in a fasted state (water consumption is permitted) and provide a spot baseline urine sample. Participants will then be served a 120g portion of onions (experimental condition), prepared under standardized conditions. Participants shall remain supervised in the laboratory and will only consume water (100mL per hour) for the subsequent 6 hours, after which participants are free to consume their habitual diet (except alcohol, tea coffee, and FVs). In the 24-hour postprandial test period, participants will obtain urine samples at several time-points. Urine collection vessels will be used to obtain samples at 0-1, 1-2, 2-4, 4-6, 6-12, 12-24 hours. This experimental protocol shall be repeated following a 4-day washout period (habitual diet consumption with no restrictions imposed on participants) with 120g of couscous consumed instead of onions, as a control condition.

Participants will report to the laboratory at 8am in a fasted state (water consumption is permitted) and provide a spot baseline urine sample. Participants will then be served a 120g portion of couscous (control condition), prepared under standardized conditions. Participants shall remain supervised in the laboratory and will only consume water (100mL per hour) for the subsequent 6 hours, after which participants are free to consume their habitual diet (except alcohol, tea coffee, and FVs). In the 24-hour postprandial test period, participants will obtain urine samples at several time-points. Urine collection vessels will be used to obtain samples at 0-1, 1-2, 2-4, 4-6, 6-12, 12-24 hours. This experimental protocol shall be repeated following a 4-day washout period (habitual diet consumption with no restrictions imposed on participants) with 120g of onions consumed instead of couscous, as an experimental condition.

The intervention includes feeding individuals a 120g portion of onions (experimental condition).

Urine samples will be analysed to putatively identify biomarkers of onion intake by comparison with control samples using high-performance liquid chromatography coupled to a quadrupole time-of-flight mass spectrometer (LC-QTOF-MS). LC-QTOF-MS analysis allows the simultaneous high-resolution measurement of a broad range of metabolites, hence the untargeted nature of the analysis. Multivariate statistical analysis and Partial least squares Discriminant Analysis included in the mass spectrometry software will be used to analyse LC-QTOF-MS results to identify features that best discriminate between test and control conditions.

First morning void urine samples will be obtained after three separate 4-day periods of supplementing evening meals with 40g, 80g and 160g of onions. The validity of candidate biomarkers from the first phase of the study, Primary Outcome 1, shall be assessed by LC-QTOF-MS - quantifying urinary concentrations following the consumption of multiple doses of onions across a range of servings.