Table 1.

In vivo and in vitro Studies showing that polyphenols inhibit glucose digestion and transport.

Animal/Human Study	Design, duration, no. of animals, doses	Outcomes	References
In vitro	0.5 mg/mL Hog pancreatic α-amylase, 500 μl of 1% starch incubated at 25 °C for 10 min Gallic acid treatments: S1 = 100% acarbose (25μM); S2 = 100% gallic acid (25μM); S3 = 50% acarbose +50% gallic acid; S4 = 75% acarbose +25% gallic acid; and S5 = 25% acarbose +75% gallic acid	S4 had the highest inhibitory effect (80%, p < 0.05)	Oboh et al. (2015)
	100 μL of α-glucosidase solution incubated at 25 °C for 10 min Gallic acid treatments: S1 = 100% acarbose (25μM); S2 = 100% gallic acid (25μM); S3 = 50% acarbose +50% gallic acid; S4 = 75% acarbose +25% gallic acid; and S5 = 25% acarbose +75% gallic acid	S3 had the highest inhibitory effect (65.7%) which is statistically similar to S1 but different from S2, S4 and S5 (p < 0.05)	Oboh et al. (2015)
	500-μl assay volume consisted of 200 μl of amylose or amylopectin, 50 μl of PBS and 50 μl of the inhibitor (extracts from green tea, strawberry, black currant and blackberry) 200 μl of 1·25 U/ml human salivary α-amylase added and incubated for 10 min of incubation at 37 °C	Green tea inhibited maltase, sucrose and iso-maltase, IC50 values of 0.02, 2.3 and 2.0 mg solid/ml water, respectively Green tea, blackberry, blackcurrant and strawberry inhibited salivary α-amylase IC50 values = 0·009, 1·2, 1·5 and 2·5mg dry powder/ml water (amylose as substrate); 0·025, 1.6, 1.7 and 3.9 mg/ml (amylopectin as substrate)	Nyambe-Silavwe et al. (2015)
	Porcine pancreatic amylase (PPA) solution (10 mL, 280 U/mL) and amyloglucosidase (AMG) solution (1 mL, 2500 U/mL) added to 100 mg of ball milled potato starch suspended in sodium acetate buffer. Mixture incubated for 120 min at 37 °C with agitation.	As tea polyphenol/Native potato starch ratios increased from 1/50 to 1/10 (w/w), levels of slowly digestible starch gradually decreased from 80.17 to 54.36% while levels of Resistant starch increased from 16.97 to 36.53% (p < 0.05)	Lv et al. (2019)
Human study	16 healthy volunteers fed on polyphenol and fibre rich foods (PFRF). PFRF was administered and blood samples collected at 0 (fasted), 15, 30, 45, 60, 90, 120, 150 and 180 min after consumption	Statistically significant (p < 0.01), dose dependent decrease in the mean postprandial glucose (-27.4 for low dose and -46.9 for high dose) Reduction of insulin area under curve (AUC) for PFRF meal (-46.9).	Nyambe-Silavwe et al. (2015)
Mice study	After 16 h overnight fast, mice in different groups were fed different rations of tea polyphenols (TPs) and native potato starch (NPS): TPs/NPS = 1/25, 1/10 w/w and starch at 1/kg body weight Blood samples collected from lateral tail vein at 0, 15, 30, 45, 60, 90 and 120 min after gavages	Native potato starch (control) had blood glucose peak after 30 min (4.9–5.6 mmol/L) while TPS/NPS combinations reached glycemic peak 45 min after gavages, showing the potential of polyphenols in delaying the glycemic peak	Lv et al. (2019)
	Male mice placed into five groups (n = 8), and were given young apple polyphenols (YAP) (150 mg/kg b.w.,), phlorizin (150 mg/kg b.w., i.g.), chlorogenic acid (150 mg/kg b.w., i.g.), tannic acid (150 mg/kg b.w., i.g.) or saline (control) for 6 days. 7th day: All mice treated with starch (5 g/kg b.w,. Blood glucose measured at 0, 30, 60, 90, 120 min after feeding.	YAP decreased the peak blood glucose level by 13.3% at 60 min and peak insulin level by 16.2% at 90 min compared to the control (p < 0.05). Decreasing effects of the phenolic compounds ordered as: Tannic acid > phlorizin > YAP > chlorogenic Acid.	Li et al., 2019
In vitro	Wheat bread and gluten-free bread were co-digested in vitro with different amount of tea polyphenols [0% GTE) 1% GTE, (50 mg) 2.5% GTE, (125mg) 5% GTE, (250 mg), 10% GTE, (500 mg), 20% GTE, (1000 mg)	Percentage of digested starch at each GTE levels (%) were 87.0, 84.0, 79.2, 64.5, 53.8 and 23.3 for 0% GTE, 1% GTE, 2.5% GTE, 5% GTE, 10% GTE and 20% GTE, respectively.	Kan et al., 2020a, Kan et al., 2020b
In vitro study	Addition of green tea extract (GTE) at 0.45%, 1%, and 2% concentration levels significantly reduced the glycaemic potential of baked and steamed bread	Bread with 2% GTE had significantly lower levels at 90 min.
Mice model	Mice were given common corn starch (5 g/kg b.w), glucose (2 g/kg b.w., i.g.), maltose (2 g/kg b.w., i.g.), or sucrose (2 g/kg b.w., i.g.) alone or in combination with EGCG (100 mg/kg b.w)	Co-treatment with EGCG significantly reduced postprandial blood glucose levels after administration of common corn starch compared to control mice (50 and 20% reduction in peak blood glucose levels and blood glucose varea under the curve, respectively). EGCG had no effect on postprandial blood glucose following administration of maltose or glucose.	Forester et al. (2012)