Fruit Fibers and green tea polyphenols reduce blood sugar levels

Normally any meal that we consume is a combination of many different foods that combine macronutrients such as protein, carbohydrates and fibers with micronutrients such as vitamins or secondary plant components such as polyphenols. So it seems to be natural that the nutrients in such a food matrix influence each other and also can act synergistically on certain parameters such as glucose absorption. It is known already that fibers in a food delay glucose absorption and that polyphenols might inhibit starch-digesting enzymes.

Polyphenol and fiber rich ingredients have shown to have several benefits e remaining components of the meal:
• α-glucosidase inhibitor (green tea)
• α-amylase inhibitors (green tea, blackberry, blackcurrant and strawberry)
• glucose transport inhibitors (apple peel and strawberry)

So that both together can work together and lower the glycaemic index of some foods was now found by a new study published in the British Journal of Nutrition.
The study explored how the addition of polyphenol- and fiber- rich food together in a starchy diet can inhibit blood sugar levels and the researchers found 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.

Study design
22 healthy participants were randomized and received controlled meals with a high dose of fruit fiber/green tea (1g green tea + 20g fruit powder) or a low dose (0,5g green tea + 10g fruitpowder).
The green tea powder was poured in 200 ml water and 20g/10g each of apple peel, blackberry, blackcurrant, and strawberry freeze-dried powders was mixed with water to make a paste and spread on bread. The meals contained 109g of white bread with 50g available carbohydrate.

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.

Results
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.

Conclusion
The consumption of foods rich in polyphenols and fiber together with bread highly significantly lower the plasma glucose levels as well as an associated attenuation of insulin release in a dose-dependent manner.

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.”

Nyambe-Silavwe H and Williamson G. 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. British Journal of Nutrition / Volume 116 / Issue 03 / August 2016, pp 443-450 (2016). http://dx.doi.org/10.1017/S0007114516002221