Table 1 Characteristics of the included studies
| Â | 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 |