Abstract
Blackcurrants are rich in polyphenolic glycosides called anthocyanins, which may inhibit postprandial glycemia. The aim was to determine the dose-dependent effects of blackcurrant extract on postprandial glycemia. Men and postmenopausal women (14M, 9W, mean age 46 years, S.D.=14) were enrolled into a randomized, double-blind, crossover trial. Low sugar fruit drinks containing blackcurrant extract providing 150-mg (L-BE), 300-mg (M-BE) and 600-mg (H-BE) total anthocyanins or no blackcurrant extract (CON) were administered immediately before a high-carbohydrate meal. Plasma glucose, insulin and incretins (GIP and GLP-1) were measured 0–120min, and plasma 8-isoprostane F2α, together with arterial stiffness by digital volume pulse (DVP) was measured at 0 and 120min. Early plasma glucose response was significantly reduced following H-BE (n=22), relative to CON, with a mean difference (95% CI) in area over baseline (AOB) 0-30min of −0.34mmol/l.h (−0.56, −0.11, P<.005); there were no differences between the intermediate doses and placebo. Plasma insulin concentrations (AOB 0–30min) were similarly reduced. Plasma GIP concentrations (AOB 0–120min) were significantly reduced following H-BE, with a mean difference of −46.6ng/l.h (−66.7, −26.5, P<.0001) compared to CON. Plasma GLP-1 concentrations were reduced following H-BE at 90min. There were no effects on 8-isoprostane F2α or vascular function. Consumption of blackcurrant extract in amounts roughly equivalent to 100-g blackcurrants reduced postprandial glycemia, insulinemia and incretin secretion, which suggests that inclusion of blackcurrant polyphenols in foods may provide cardio-metabolic health benefits. This trial was registered at clinicaltrials.gov as NCT01706653.
Highlights
Evidence is emerging that fruit polyphenols may have wide ranging beneficial effects on vascular and metabolic health [1]
This study aimed to investigate whether blackcurrant anthocyanin-rich fruit drinks could inhibit the rise in blood glucose concentrations following a high-carbohydrate meal in a healthy population
The highest dose of blackcurrant anthocyanins inhibited the rate of the increase in plasma glucose and insulin concentrations in the first 30 min, had an inhibitory effect on plasma Glucose-dependent insulinotropic polypeptide (GIP) concentrations up to 90 min post-meal and reduced plasma Glucagon-like peptide-1 (GLP-1) concentrations at ~90 min, but the lower doses had no significant inhibitory effects
Summary
Evidence is emerging that fruit polyphenols may have wide ranging beneficial effects on vascular and metabolic health [1]. Among the long list of potential fruit bioactives are the anthocyanins: polyphenolic glycosides belonging to the flavonoid family that vividly pigment berries and other plant foods. The aglycones of anthocyanins, anthocyanidins, include delphinidin, petunidin, cyanidin, malvidin, pelargonidin and peonidin. Glycosylation can involve glucose, galactose, rhamnose and arabinose or various combinations of these sugars. There may be acylation with p-coumaric, ferulic, caffeic, sinapic, malonic, acetic or phydroxybenzoic acids. Blackcurrants are rich in delphinidin-3-rutinoside, cyanidin-3rutinoside, delphinidin-3-glucoside and cyanidin-3-glucoside, as well as condensed tannins (proanthocyanidins), oligomeric and polymeric chains of flavan-3-ols [2]
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