Polyphenol- and fibre-rich dried fruits with green tea attenuate starch-derived postprandial blood glucose and insulin: a randomised, controlled, single-blind, cross-over intervention

Br J Nutr. 2016 Aug;116(3):443-50. doi: 10.1017/S0007114516002221. Epub 2016 Jun 9.


Polyphenol- and fibre-rich foods (PFRF) have the potential to affect postprandial glycaemic responses by reducing glucose absorption, and thus decreasing the glycaemic response of foods when consumed together. A randomised, single-blind, cross-over study was conducted on sixteen healthy volunteers to test whether PFRF could attenuate postprandial blood glucose in healthy volunteers when added to a source of carbohydrate (starch in bread). This is the first study to examine the effects of a meal comprised of components to inhibit each stage of the biochemical pathway, leading up to the appearance of glucose in the blood. The volunteers were fasted and attended four visits: two control visits (bread, water, balancing sugars) and two test visits (single and double dose of PFRF) where they consumed bread, water and PFRF. Blood samples were collected at 0 (fasted), 15, 30, 45, 60, 90, 120, 150 and 180 min after consumption. The PFRF components were tested for α-amylase and α-glucosidase inhibitory potential in vitro. Plasma glucose was lower after consumption of both doses compared with controls: lower dose, change in mean incremental areas under the glucose curves (IAUC)=-27·4 (sd 7·5) %, P<0·001; higher dose, IAUC=-49·0 (sd 15·3) %, P<0·001; insulin IAUC was also attenuated by-46·9 (sd 13·4) %, P<0·01. Consistent with this, the polyphenol components of the PFRF inhibited α-amylase (green tea, strawberry, blackberry and blackcurrant) and α-glucosidase (green tea) activities in vitro. The PFRF have a pronounced and significant lowering effect on postprandial blood glucose and insulin response in humans, due in part to inhibition of α-amylase and α-glucosidase, as well as glucose transport.

Keywords: α-Amylase; α-Glucosidase; Diabetes; Fibre; GI glycaemic index; IAUC incremental areas under the glucose curves; IC50 concentration required for 50 % inhibition; PFRF polyphenol- and fibre-rich food; Polyphenols; Postprandial glucose.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Area Under Curve
  • Blood Glucose / metabolism*
  • Bread
  • Camellia sinensis / chemistry*
  • Cross-Over Studies
  • Dietary Fiber / pharmacology*
  • Fragaria / chemistry
  • Fruit / chemistry*
  • Healthy Volunteers
  • Humans
  • Insulin / blood*
  • Plant Extracts / pharmacology
  • Polyphenols / pharmacology*
  • Postprandial Period*
  • Ribes / chemistry
  • Rubus / chemistry
  • Single-Blind Method
  • Starch / blood
  • Tea / chemistry
  • alpha-Amylases / metabolism
  • alpha-Glucosidases / metabolism


  • Blood Glucose
  • Dietary Fiber
  • Insulin
  • Plant Extracts
  • Polyphenols
  • Tea
  • Starch
  • alpha-Amylases
  • alpha-Glucosidases