“It is the normal way in which most foods are consumed—that is, as a total meal in combination with other foods,” the researchers from the School of Food Science and Nutrition at the University of Leeds wrote in their report.
Published in the British Journal of Nutrition, the study reported observations that polyphenol- and fiber-rich foods “have pronounced and significant lowering effects on postprandial blood glucose and insulin response in humans, due in part to inhibition of alpha-amylase and a-glucosidase,” it said.
Study design
The researchers randomized 22 participants to receive different orders of a control high dose, or low dose meal. All meals contained 109g of white bread with 50g available carbohydrate.
Polyphenol and fiber rich ingredients were selected for the remaining components of the meal: α-glucosidase inhibitor (green tea), α-amylase inhibitors (green tea, blackberry, blackcurrant and strawberry), and glucose transport inhibitors (apple peel and strawberry), with all fruits providing some fiber.
The higher dose included 1 g of green tea powder in 200 ml water, with 20 g each of apple peel, blackberry, blackcurrant, and strawberry freeze-dried powders mixed with water to make a paste and spread on bread.
The lower dose of the test meal contained half the amount of fruits and green tea with half the amounts of balancing sugars dissolved in 200 ml water to equalise the amount of sugars present in all doses.
The control meal included 0.8, 5.4 and 8.6 g of sucrose, glucose and fructose, respectively, dissolved in 200 ml water to standardise the amounts of sugars present in the extracts of the high dose. This meal was consumed on two visits to determine and variation in the measurements.
Findings
Both test diets with the polyphenol- and fiber-rich ingredients showed a significant dose-dependent decrease in the mean incremental areas under the glucose curves compared to the control meal. There were no significant differences between the high and low dose meals.
Researchers found that “consumption of foods rich in polyphenols and fiber together with bread resulted in a highly significant dose-dependent lowering of the glucose [area under the blood glucose response curve], as well as an associated attenuation of insulin,” they wrote.
It wasn’t possible to define the exact contribution of inhibition of the different steps to the attenuation of blood glucose, they wrote, but the researchers speculated that “partial inhibition of multiple steps is important for the observed effect on the glycemic response,” causing reductions that can “play a major, long-term role in the management or risk reduction of diabetes type 2.”
Source: British Journal of Nutrition
Published online ahead of print, http://dx.doi.org/10.1017/S0007114516002221
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
Authors: H. Nyambe-Silavwe and G. Williamson