Table 3.

Reduction and oxidation reaction of gut microbes to natural products.

Classification	Gut microbiota	Enterobacterial metabolic enzyme	Substrate	End-product	Changes	Ref.
Flavonoids	Clostridium sp. strain HGH6; Lactobacillus sp. Niu-O16	Dihydrodaidzein reductase; tetrahydrodaidzein reductase	Daidzein	Dihydrodaidzein; tetrahydrodaidzein	Anti-osteoporosis↑	Wang et al. (2007) and Heng et al. (2019)
	Aeroto Niu-O16	NA	Genistein	Dihydrogenistein	Bioavailability↑	Mace et al. (2019)
	Rat gut microbes E. ramulus	Flavone reductase	Quercetin	Kaempferol; taxifolin	Bioavailability↑	Qin et al. (2017)
	E. ramulus	Flavanone-/flavanonol-cleaving reductase	Xanthohumol; O-desmethylxanthohumol	α, β-dihydroxanthohumol; O-desmethyl-α, β-dihydroxanthohumol	Anti-bacterial↑	Paraiso et al. (2019)
Alkaloids	Mouse gut microbes	Nitroreductase	BBR; coptisine	dhBBR; hydrogenated berberine	Bioavailability↑ anti-inflammatory↑	Feng et al. (2015) and Cui et al. (2018)
	Mouse gut microbes	NA	BBR	Oxyberberine	Anti-fungal↑	Li C. et al. (2020)
	Mouse/human gut microbes	NA	Avenanthramide-C	Dihydroavenanthramide-C	Anti-inflammation↑ anti-atherogenesis↑	Wang P. et al. (2015)
Phenolic acids	Human gut microbes	NA	CAA	Dihydrocaffeic acid	Bioavailability↑	Gonthier et al. (2006) and García-Villalba et al. (2020)
	Rat gut microbes	NA	Isoferulic acid	Dihydrocaffeic acid	Anti-oxidant↑ anti-apoptosis↑	Kay et al. (2017)
	Rat gut microbes	NA	Dansensu	3-phenyl-2-hydroxy propionic acid; 3-(3,4-dihydroxy phenyl) 2-acrylic acid; 3-(3,4-dihydroxy phenyl)-propionate	Bioavailability↑	Gu et al. (2014)
	Gordonibacter urolithinfaciens	Catechol-dehydroxylase	Chlorogenic acid; rosmarinic acid	Dihydro-chlorogenic acid; dihydro-rosmarinic acid	Bioavailability↑	García-Villalba et al. (2020)
Terpenoids	Ruminococcus sp. po1-3	3β-hydroxysteroid dehydrogenase	Glycyrrhetinic acid	3-oxo-glycyrrhetinic acid	Anti-inflammatory↑
Anthraquinone	Human gut microbes; Streptococcus spp.	NA	Sennoside-8-O-monoglycoside	Rhubaranthrone	Purgation↑	Hattori et al. (1988) and Matsumoto et al. (2012)
Stilbenes	Slackia equolifaciens; Eggerthella lenta ATCC 4305	NA	Resveratrol	Dihydroresveratrol	Anti-oxidant↑	Jung et al. (2009), Bode et al. (2013) and Pallauf et al. (2019)
Diketones	E. coli strain K-12; E. fergusonii ATCC 35469; E. coli strains ATCC 8739 and DH10B	CurA	Curcumin	DHC; THC	Anti-oxidant↑ lipid-lowering↑	Hassaninasab et al. (2011) and Tan et al. (2014)
Steroids	Eubacterium lenta	Cardiac glycoside reductase	Digoxin	Dihydrodigoxin	Bioavailability↓	Kumar et al. (2018)
Other classes	Human gut microbes	NA	Aristolochic acid	Aristololactams	Anti-cancer↑	Feng et al. (2019)