Table 2.

Childhood obesity database of included papers

Continent	Reference paper	Study population, location and number of participants (N)	Measurement technique	Focus area	Matrix	Study design	Pubertal stage	Outcome/related disease	Diagnostics
Asia	Cho et al. (2017) Pediatric Obesity	Korea N = 184	Liquid chromatography–mass spectrometry (LC–MS)/MS and flow injection analysis (FIA)–MS/MS	Metabolomics	Urine	Cohort	> TS1	Obesity	BMI according to Korean National Growth Charts
	Kim et al. (2016) The Journal of Clinical Endocrinology & Metabolism	Korea N = 242	Gas chromatography (GC)–MS	Steroid metabolites	Serum	Case–control	> 50% TS1 and < 50% TS2, TS3 and TS4	Obesity	BMI according to Korean National Growth Charts
	Lee et al. (2018) Scientific Reports	Korea, KoCAS N = 430	LC–MS/MS	Metabolomics	Plasma	Cohort	> TS1	Obesity and diabetes type 2	BMI according to Korean National Growth Charts
	Lee et al. (2019) Scientific Reports	Korea, KoCAS-1 N = 449	FIA–MS/MS	Amino acids	Plasma	Cohort	< 5% TS1, > 45% TS2 and TS3 and > 45% TS4 and TS5	Obesity and insulin resistance	BMI according to Korean National Growth Charts
	Son et al. (2015) The Journal of Steroid Biochemistry and Molecular Biology	Korea N = 253	GC–MS	Cholesterol and other sterols	Serum	Case–control	TS1 and TS2	Obesity	BMI according to Korean National Growth Charts
	Suzuki et al. (2019) BMC Pediatrics	Japan N = 26	LC–MS	Amino acids	Plasma	Cohort		Obesity, impaired glucose tolerance and hyperuricemia	BMI according to Korean National Growth Charts
Australia	Saner et al. (2019) Metabolomics	Victoria, COBRA N = 412	1H-NMR	Amino acids	Serum	Cohort	> 30% TS1, 25% TS2 and TS3 and 35% TS4 and TS5	Obesity	US Centres for Disease Control (CDC) growth reference charts
Europe	Anjos et al. (2019) Journal of Proteome Research	Portugal N = 32	GC–MS and hydrophilic interaction (HI)LC–MS2, untargeted and 163 targets	Phospholipids	Serum	Case–control	> TS1	Obesity	Global BMI ranges (Centro Hospitalar do Baixo Vouga, Portugal)
	Hosking et al. (2019) Pediatric Diabetes	Early Bird, United Kingdom N = 150	1H-NMR	Amino acids	Serum	Longitudinal cohort	TS1 at baseline and ≧ TS3 at follow-up	Insulin resistance	BMI according to British 1990 standards
	Lau et al. (2018) BMC Medicine	HELIX, Multilevel European (UK, France, Spain, Norway, Greece, Lithuania) N = 1192	FIA–MS2 and LC–MS2 and 1H-NMR, Fingerprinting	Metabolomics	Serum and urine	Longitudinal cohort	TS1 and TS2	Not specified	WHO growth reference curves
	Mangge et al. (2016) The Journal of Nutritional Biochemistry	Austria N = 666	HPLC	Amino acids	Serum	Case–control	≧ TS3	Obesity	Austrian reference BMI percentiles and HOMA-IR
	Martos-Moreno et al. (2017) International Journal of Obesity	Spain N = 100	GC–MS2 and LC–MS2	Glycero-phospholipids	Serum	Case–control	TS1	Obesity	BMI-SDS according to Spanish standards and IOTF classification by Cole’s LMS method
	Mastrangelo et al. (2016) International Journal of Obesity	Spain N = 458	GC–MS2 and LC–MS2	Glycero-phospholipids	Serum	Case–control	TS1	Obesity	BMI-SDS according to Spanish standards
	Reinehr et al. (2015) European Journal of Nutrition	Germany N = 160	LC–MS2	Glycero-phospholipids	Serum	Case–control	TS1 and TS2	Obesity	BMI according to German reference data
	Rocha et al. (2018) Hormone Research in Paeditrics	Germany N = 458	Biochemical technique	Uric acid	Serum	Case–control	≧ TS1	Obesity	BMI according to German reference data
	Troisi et al. (2017) Nutrients	Italy N = 40	GC–MS	Metabolomics	Urine	Case–control	TS1, TS2, TS3 and TS4	Obesity and non-alcoholic fatty liver disease	Italian reference BMI percentiles (aged 2 to 20 years)
	Troisi et al. (2019) Nutrients	Italy N = 41	GC–MS	Metabolomics	Saliva	Case–control	≧ TS1	Obesity and non-alcoholic fatty liver disease	Italian reference BMI percentiles (aged 2 to 20 years)
	Valle et al. (2015) Pediatric Diabetes	Spain N = 86		Uric acid	Serum	Case–control	TS1	Metabolic syndrome	Spanish reference BMI percentiles (Curvas y tablas de crecimiento, 6–9 year old)
	Wahl et al. (2012) Obesity Facts	Germany N = 120	LC–MS2	Glycero-phospholipids	Serum	Case–control	TS1, TS2, TS3 and TS4	Obesity	IOTF classification by Cole’s LMS method
	Wijnant et al. (2020) Analytical Chemistry	Belgium N = 140	LC–MS	Metabolomics	Saliva	Case–control	≧ TS1	Obesity	BMI z-scores following Roelants et al. and IOTF classification by Cole’s LMS method
	Zhang et al. (2019) Journal of Adolescent Health	Finland N = 396	1H-NMR	Amino acids	Serum	Longitudinal cohort	TS1 and TS2 at baseline and TS5 at follow-up	Insulin resistance	Finnish reference BMI data (aged 0 to 20 years)
America	Aristizabal et al. (2017) Nutrients	Colombia N = 58	GC	FFA	Plasma	Case–control	TS1	Obesity	WC reference cut-off according to IDEFICS
	Bermudez-Cardona and Velasquez-Rodriguez (2016) Nutrients	Colombia N = 96	GC-FID	Fatty acids	Serum	Case–control	> 10% TS1, 25% TS2, TS3 and TS4 and > 60% TS5	Metabolic syndrome	WHO growth reference curves
	Butte et al. (2015) The American Journal of Clinical Nutrition	Texas N = 803	GC–MS and UPLC–MS/MS	Metabolomics	Plasma	Cohort	TS2, TS3 and TS4	Obesity	Reference BMI percentiles according to CDC growth charts for the United States of America
	Chavira-Suárez et al. (2020) PLoS ONE	Mexico N = 168	Tandem MS	Metabolomics	Serum	Case–control		Overweight and obesity	WHO growth reference curves and WHtR in z-scores NHANES
	McCormack et al. (2013) Pediatric Obesity	Massachusetts N = 21	Biochemical technique	Metabolomics	Serum	Case–control	TS2, TS3 and TS4	Obesity	Reference BMI percentiles according to CDC growth charts for the United States of America
	Farook et al. (2015) Pediatric Obesity	Texas N = 42	UPLC–MS/MS	Metabolomics	Serum	Case–control	TS1, TS2 and TS3	Obesity	NHANES III
	Flannagan et al. (2018) Nutrition, Metabolism and Cardiovascular disease	El Salvador, Honduras, Nicaragua, Panama, Costa Rica, Belize, the Dominican Republic and Guatemala N = 201	GC	Metabolomics	Adipose tissue	Cohort	TS1	Metabolic syndrome	BMI-z according to WHO Growth Reference (for children aged 5 to19 years)
	Goffredo et al. (2017) Nutrients	Connecticut N = 78	LC–MS	Branched-chain amino acids	Plasma	Case–control	TS1, TS2, TS3, TS4 and TS5	Non-alcoholic fatty liver disease	National BMI and BMI-z reference percentiles (Yale Pediatric NAFLD Cohort)
	Higgins et al. (2020) The Journal of Clinical Endocrinology and Metabolism	Canada N = 45	LC–MS/MS	Lipoproteins and bile acids	Serum	Cohort	< 5%% TS2, 25% TS3, 30% TS4 and > 40% TS5	Obesity	WHO growth reference curves
	Mauras et al. (2015) The Journal of Clinical Endocrinology and Metabolism	Florida N = 35	LC–MS/MS	Estrogens	Plasma	Case–control	TS1	Obesity	National reference BMI percentiles (Florida)
	Moran-Ramos et al. (2017) Scientific Reports	Mexico N = 1120	MS/MS	Amino acids	Serum	Cohort	TS1 and TS2	Obesity	Reference BMI percentiles according to CDC growth charts for the United States of America
	Newbern et al. (2014)The  Journal of Clinical Endocrinology and Metabalism	North Carolina N = 82	MSn	Metabolomics	Plasma	Cohort	TS2, TS3, TS4 and TS5	Insulin resistance	Reference BMI percentiles according to CDC growth charts for the United States of America
	Perng et al. (2017) Paediatric Obesity	Mexico N = 238	LC–MS	Metabolomics	Serum	Cohort	35% TS1, < 10% TS2, 5% TS3 and 5% TS 4, TS5	Metabolic risk	Reference BMI percentiles (Mexico National Institute of Public Health)
	Perng et al. (2018) Pediatric Obesity	Massachusetts N = 213	Ultra-high performance (UP)LC–MS/MS	Amino acids	Plasma	Longitudinal cohort	> 65% TS1 and ≧ 30% TS2	Early adolescence	Reference BMI and BMI-z percentiles according to CDC growth charts for the United States of America
	Perng et al. (2019) Pediatric Research	Mexico N = 179	LC–MS	Amino acids	Serum	Longitudinal cohort	TS1 at baseline and > TS2 after 5-year follow-up	Metabolic risk	National reference BMI-z scores (Mexico National Institute of Public Health)
	Perng et al. (2020a; b) Obesity	Massachusetts N = 592	UPLC–MS	Metabolomics	Plasma	Case–control	> 10% TS1 and ≧ 80% TS2	Metabolic risk	Reference BMI and BMI-z percentiles according to CDC growth charts for the United States of America
	Short et al. (2019) The Journal of Clinical Endocrinology and Metabolism	Oklahoma N = 94	UPLC–MS	Amino acids	Plasma	Case–control	≧ TS2	Obesity	Reference BMI percentiles according to CDC growth charts for the United States of America
	Trico et al. (2017) The Journal of Clinical Endocrinology and Metabolism	Connecticut N = 78	1H-NMR	Amino acids	Plasma	Longitudinal cohort	> TS1	Insulin resistance	National BMI-z reference (the Yale Pediatric Obesity Clinic)
	Trico et al. (2019) Antioxidants and Redox Signaling	Connecticut N = 122	LC–MS/MS	Fatty acids	Plasma	Case–control	> TS1	Metabolic syndrome	National BMI-z reference (the Yale Pediatric Obesity Clinic)

An overview of the included studies according to the continental region of study. The first author, year of publication and name of the journal were addressed as reference. For every study, the study population, location of the study, number of participants, measurement technique, focus area of research, the matrix studied, the study design, pubertal stage of the children under study, the main outcome and method of diagnosis (in defining the groups under study) were listed