Apple and Blackcurrant Polyphenols Reduce Postprandial Glycemia

by | Nov 12, 2018 | 2017, Blood Sugar, Diabetes

Written by Angeline A. De Leon, Staff Writer. Twenty-five healthy study participants, who consumed an apple and blackcurrant polyphenol-rich beverage, significantly decreased postprandial glycemia within the first half hour of consuming a high-carbohydrate meal and maintained the inhibitory effect for up to two hours post-meal.

Postprandial hyperglycemia is an exaggerated rise in blood sugar following a serving of food. A diet high in carbohydrates carries a high glycemic load and may contribute to risk of type 2 diabetes 1. There is evidence to suggest that the polyphenols contained in certain fruits can reduce postprandial glucose levels 2,3. For example, polyphenols from apples and berries have been shown to attenuate glucose absorption by acting as inhibitors of glucose transporters (SGLT1 and GLUT2) 4-6. In animal research, apple polyphenol extract has been shown to improve insulin resistance 7, and a recent randomized controlled trial reported that a beverage containing anthocyanin-rich (plant pigments with antioxidant effects) blackcurrant extract (1600 mg blackcurrant polyphenols) was capable of decreasing postprandial glycemia following consumption of starch and sucrose load 8. To verify whether consumption of beverages containing extracts of polyphenol-rich apple and anthocyanin-rich blackcurrant could decrease postprandial glycemic response, researchers from King’s College London (2017) 9 measured the effects of a mixture of apple and blackcurrant polyphenol extract on postprandial blood glucose concentrations following a starch- and sucrose-containing meal.

Using a randomized, controlled, double-blind, cross-over trial, researchers recruited a total of 20 healthy men (mean age = 26 years) and 5 post-menopausal women (mean age = 57 years) as subjects for an intervention conducted over a period of 7 months. Participants received one of three test drinks consisting of highly purified fruit extracts (a placebo drink containing no polyphenols, CON; a polyphenol-rich drink containing 1200 mg apple polyphenols, AE; and a polyphenol-rich drink containing 600 mg apple polyphenols plus 600 mg blackcurrant anthocyanins, AB + BE) in random order at three separate study visits with a wash-out period of at least seven days between each visit. Prior to each visit, participants consumed a low-fat meal the evening before and fasted for 12 hours, then during the study visit, drank the beverage immediately before consuming a high-carbohydrate meal. Blood samples were taken prior to drinking and at incremental periods following the start of the meal. Researchers analyzed blood samples for glucose, insulin, C-peptide (parameter of insulin secretion), and glucose-dependent insulinotropic polypeptide (GIP, hormone released in response to nutrient stimulation, enhances release of insulin) and calculated postprandial glycemic response (incremental area under the curve for plasma glucose concentrations, iAUC).

Compared with CON, AE + BE significantly lowered iAUC 0-30 min (mean difference = -32 mmol/L min, 95% CI: -41 to –22, p < 0.0005) and iAUC 0–120 min (mean difference = -52 mmol/L min, 95% CI: -94 to –9, p < 0.05). Compared with CON, AE also significantly reduced iAUC 0-30 min (mean difference = -26 mmol/L min, 95% CI: -35 to –18, p < 0.0005), but not iAUC 0-120. Both AE + BE and AE treatments significantly reduced postprandial insulin, C-peptide, and GIP concentrations, relative to CON (iAUC 0-30 min, p < 0.005 for all). Additional in vitro analysis using human intestinal cells (Caco-2 cells) also showed a dose-response effect of both apple extract and blackcurrant extract on total glucose uptake in intestinal cells, suggesting inhibition of intestinal glucose transport by the polyphenol extracts.

Based on study findings, consumption of apple and blackcurrant polyphenols appears to improve postprandial glycemia within the first half hour of high-carbohydrate food intake, with the combination of both polyphenol extracts showing a greater inhibitory effect lasting up to 2 hours post-meal. Thus, the metabolic effects of fruit intake may be cumulative, with larger doses of polyphenols and anthocyanins providing greater benefits for glucose absorption. Ingestion of apple and blackcurrant polyphenols may be particularly advisable for individuals at risk of diabetes. Strengths of the study involve the use of highly purified fruit extracts to avoid the confounding effect of fruit fiber and the incorporation of secondary in vitro analyses, which provided evidence to support the inhibitory effects of polyphenol extracts on glucose transport.

Source: Castro-Acosta ML, Stone SG, Mok JE, et al. Apple and blackcurrant polyphenol-rich drinks decrease postprandial glucose, insulin and incretin response to a high-carbohydrate meal in healthy men and women. Journal of Nutritional Biochemistry. 2017; 49: 53-62. DOI: 10.1016/j.jnutbio.2017.07.013.

© 2017 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Posted November 12, 2018.

Click here to read the full text study.

Angeline A. De Leon, MA, graduated from the University of Illinois at Urbana-Champaign in 2010, completing a bachelor’s degree in psychology, with a concentration in neuroscience. She received her master’s degree from The Ohio State University in 2013, where she studied clinical neuroscience within an integrative health program. Her specialized area of research involves the complementary use of neuroimaging and neuropsychology-based methodologies to examine how lifestyle factors, such as physical activity and meditation, can influence brain plasticity and enhance overall connectivity.

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