Table 1.

Characteristics of the included studies

	Study attributes/characteristics of groups studied
Inclusion criteria
Study design	Population-based observational studies and (experiment) trials: case–control, cohort and case-series
Population/age	Children and/or adolescents (0–19 yearsa)
Outcome	Obesity and/or related metabolic abnormalities (impaired glucose tolerance, insulin resistance, prediabetes, diabetes mellitus type 2, metabolic syndrome) in metabolomics research
Biofluid	Blood (serum and plasma), urine, excretion, faeces, saliva, tissue, hair, nails
Diagnostics	Clinician-based: BMI diagnostic criteria, oral glucose tolerance test, parameters/criteria for metabolic syndrome, cardiovascular disease risk, non-alcoholic fatty liver disease, etc
Exclusion criteria
Language	Language other than English
Document type	Other than article (e.g. review, letters, conference abstracts)
Age/disease	Study population of adults only and in utero/maternal studies (e.g. gestational diabetes), participant population with any thyroid or metabolic disorder under treatment (e.g. diabetes, cardiovascular disease)
Type of study	Exposure study, genomics, transcriptomics, proteomics, microbiomics and intervention studies

A detailed description of the in- and exclusion criteria on the basis of which articles were retrieved and selected articles were withheld for final assessment

^aBased on WHO definition