Table 3.
Overview of the validation criteria for candidate intake biomarkers.
| Substrate | Biomarker | Plausibility | Dose–Response | Time–Response | Robustness | Reliability | Stability | Analytical Performance | Reproducibility | |
|---|---|---|---|---|---|---|---|---|---|---|
| Polyphenolic compounds | Urine | Dihydro caffeic acid 3-O-sulfate | Y | U | U | Y | U | U | U | U |
| Polyphenolic compounds | Urine | Hippuric acid | Y | U | U | U | Y | Y | Y | Y |
| Citrus | Urine | Proline betaine | Y | U | U | U | U | U | Y | U |
| Beans | Urine | NMNA | Y | U | U | U | U | U | Y | U |
| Coconut | Urine | Scyllo-inositol | Y | U | U | U | U | U | Y | U |
| Beans | Serum | Acetylornithine | Y | U | U | U | U | U | Y | U |
NMNA: N-methylnicotinic acid. Q1: Is the marker compound plausible as a specific biomarker for the food or food group (chemical/biological plausibility)? Q2: Is there a dose–response relationship at relevant intake levels of the targeted food (quantitative aspect)? Q3: Is the biomarker kinetics described adequately to make a wise choice of sample type, frequency, and time window (time–response)? Q4: Has the marker been shown to be robust after intake of complex meals reflecting dietary habits of the targeted population (robustness)? Q5: Has the marker been shown to compare well with other markers or questionnaire data for the same food/food group (reliability)? Q6: Is the marker chemically and biologically stable during biospecimen collection and storage, making measurements reliable and feasible (stability)? Q7: Are analytical variability (CV%), accuracy, sensitivity, and specificity known to be adequate for at least one reported analytical method (analytical performance)? Q8: Has the analysis been successfully reproduced in another laboratory (reproducibility)? Y = yes; U = unknown.