Abstract
Polyphenols, including flavonoids, phenolic acids, proanthocyanidins and resveratrol, are a large and heterogeneous group of phytochemicals in plant-based foods, such as tea, coffee, wine, cocoa, cereal grains, soy, fruits and berries. Growing evidence indicates that various dietary polyphenols may influence carbohydrate metabolism at many levels. In animal models and a limited number of human studies carried out so far, polyphenols and foods or beverages rich in polyphenols have attenuated postprandial glycemic responses and fasting hyperglycemia, and improved acute insulin secretion and insulin sensitivity. The possible mechanisms include inhibition of carbohydrate digestion and glucose absorption in the intestine, stimulation of insulin secretion from the pancreatic β–cells, modulation of glucose release from the liver, activation of insulin receptors and glucose uptake in the insulin-sensitive tissues, and modulation of intracellular signalling pathways and gene expression. The positive effects of polyphenols on glucose homeostasis observed in a large number of in vitro and animal models are supported by epidemiological evidence on polyphenol-rich diets. To confirm the implications of polyphenol consumption for prevention of insulin resistance, metabolic syndrome and eventually type 2 diabetes, human trials with well-defined diets, controlled study designs and clinically relevant end-points together with holistic approaches e.g., systems biology profiling technologies are needed.
Highlights
Polyphenols are a large and heterogeneous group of phytochemicals of plant-based foods, such as tea, coffee, wine, cereal grains, vegetables, legumes, fruits and berries
For substantiation of the benefits of polyphenols in the control of postprandial glucose homeostasis, more clinical studies involving subjects with normal and impaired glucose metabolism are needed. These studies should be focused on the effects of dietary polyphenols on glycemic responses induced by starch and sucrose, the main highglycemic carbohydrates in our diet
Regular consumption of diets with high glycemic impact may increase the risk of obesity, type 2 diabetes and cardiovascular disease by promoting excessive food intake, pancreatic
Summary
Polyphenols are a large and heterogeneous group of phytochemicals of plant-based foods, such as tea, coffee, wine, cereal grains, vegetables, legumes, fruits and berries. The dietary recommendations for individuals at risk of type 2 diabetes emphasise the intake of plant food products, such as whole grains, berries, fruits and vegetables, all known to be excellent sources of dietary fibre, and good sources of variable polyphenolic compounds. These compounds may influence glucose metabolism by several mechanisms, such as inhibition of carbohydrate digestion and glucose absorption in the intestine, stimulation of insulin secretion from the pancreatic cells, modulation of glucose release from liver, activation of insulin receptors and glucose uptake in the insulin-sensitive tissues, and modulation of hepatic glucose output (Figure 1). Inhibition of the digestive enzymes or glucose transporters would reduce the rate of glucose release and absorption in the small intestine and suppress postprandial hyperglycemia
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