Table I.

Excluded studies.

No.	Study	Reason for exclusion	(Refs.)
1	Ma et al, 2010	The study used subjects with surgical intervention	(9)
2	Bertini et al, 2012	Patients with CRC with chemotherapy intervention	(10)
3	Zhu et al, 2014	Targeted metabolomics	(11)
4	Zhu et al, 2015	Targeted metabolomics	(2)
5	Guertin et al, 2015	The study investigated the association between CRC and coffee consumption	(12)
6	Dowling et al, 2015	Proteomic studies	(13)
7	Crotti et al, 2016	Targeted metabolomics; focus was on lipid metabolism	(14)
8	Farshidfar et al, 2012	Metabolite profile was not reported	(15)
9	Farshidfar et al, 2016	Patients with CRC undergoing chemotherapy	(16)
10	Vahabi et al, 2017	Comparing normal and stage I CRC	(17)
11	Shu et al, 2018	Sample collection prior to cancer diagnosis	(18)

CRC, colorectal cancer.