Abstract
Growing evidence from animal studies supports the anti-diabetic properties of some dietary polyphenols, suggesting that dietary polyphenols could be one dietary therapy for the prevention and management of Type 2 diabetes. This review aims to address the potential mechanisms of action of dietary polyphenols in the regulation of glucose homeostasis and insulin sensitivity based on in vitro and in vivo studies, and to provide a comprehensive overview of the anti-diabetic effects of commonly consumed dietary polyphenols including polyphenol-rich mixed diets, tea and coffee, chocolate and cocoa, cinnamon, grape, pomegranate, red wine, berries and olive oil, with a focus on human clinical trials. Dietary polyphenols may inhibit α-amylase and α-glucosidase, inhibit glucose absorption in the intestine by sodium-dependent glucose transporter 1 (SGLT1), stimulate insulin secretion and reduce hepatic glucose output. Polyphenols may also enhance insulin-dependent glucose uptake, activate 5′ adenosine monophosphate-activated protein kinase (AMPK), modify the microbiome and have anti-inflammatory effects. However, human epidemiological and intervention studies have shown inconsistent results. Further intervention studies are essential to clarify the conflicting findings and confirm or refute the anti-diabetic effects of dietary polyphenols.
Highlights
Type 2 diabetes (T2D) is a chronic disease of metabolic dysregulation, most notably abnormal glucose metabolism, accompanied by complications including cardiovascular disease, retinopathy, nephropathy, neuropathy, leg ulcers and gangrene [1]
A study [116] in 60 subjects with T2D treated with sulfonylureas found significant reductions in fasting glucose (18%–29%), triglycerides (23%–30%), low-density lipoprotein (LDL) (7%–27%), and total cholesterol (12%–26%), following supplementation with either 1, 3, or 6 g of cassia cinnamon daily for 40 days, while no change was observed in the placebo group but the groups again were not compared statistically
In a randomized, controlled study of 38 males with at least one component of metabolic syndrome [127], the daily consumption of 20 g of wine grape pomace flour containing 10 g of dietary fiber, 822 mg of polyphenols for 16 weeks showed a significant reduction (p < 0.05) in postprandial insulin and fasting glucose levels compared with the baseline, but there were no significant differences in fasting insulin, postprandial glucose, insulin, glycosylated haemoglobin and homeostasis model assessment of insulin resistance (HOMA–IR) between a wine grape pomace flour group and a control group [127]
Summary
Type 2 diabetes (T2D) is a chronic disease of metabolic dysregulation, most notably abnormal glucose metabolism, accompanied by complications including cardiovascular disease, retinopathy, nephropathy, neuropathy, leg ulcers and gangrene [1]. In 2013, 382 million people were estimated to have diabetes globally and this number is projected to be 592 million by 2035 [2]. Identification of modifiable lifestyle factors including dietary factors that reduce the incidence of T2D is a vital area of research [3,4]. Dietary polyphenols have been suggested to lower the risk of T2D [5,6,7]. This review aims to summarize relevant epidemiological and clinical studies linking polyphenol-rich foods to the risk of T2D, and to describe the multiple mechanisms of action of polyphenol-rich foods through which these effects are mediated
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