Table 2 Typical features of an extensive literature search methodology on BFIs

Steps

Characteristics of the step

1. Designing the review for a specific food group

Objective: Identify and evaluate existing biomarkers for dietary assessment for a specific food or food group.

2. Searching for relevant BFI research papers

Eligibility criteria for inclusion or exclusion of studies: Pre-defined and objectively applied.

Inclusion criteria: Eligible study designs should include any human study with a well-documented intake of the targeted food.

Exclusion criteria: Defined case by case by objective criteria.

Description of the review method: Systematically documented.

Literature search: Structured in order to identify the highest number of relevant results, documented and reproducible.

3. Selecting and screening papers for quality and relevance

Defined procedure, documented results: Identification of a list of publications containing information and/or applications of possible food biomarkers related to the consumption of a specific food or food group.

4. Selection of candidate BFIs and data collection from the included records

Procedure: Identification of possible candidate biomarkers and systematic extraction of information to evaluate the usefulness of each compound as BFIs.

5. Assessing quality of included papers on candidate BFIs

Methodological quality assessment of included studies: Evaluation of results in intervention and observational studies.

Evaluating risk of bias (false positive identification, missing entries).

6. Evaluating the current overall status of BFIs for the food group in question

Synthesis: Systematic synthesis of the information to evaluate the specificity and the presence of other quality information (robustness, kinetic properties, dose-response, etc.) on each candidate BFI. Preparing for systematic validation

7. Presenting data and results

Reporting of study results: Reporting of the paper containing candidate biomarkers in structured tables and in the text; non-selected markers are listed in a supplementary list.

8. Interpretation and conclusion

Overall assessment: The usefulness of the candidate BFIs and/or suggest possible candidate biomarkers or combinations of markers for further investigation and validation.