Could Polyphenolic Food Intake Help in the Control of Type 2 Diabetes? A Narrative Review of the Last Evidence

Background: Diabetes is one of the most serious global public health concerns, imposing a significant burden on public health and socio-economic development, with type 2 diabetes accounting for 90 percent of individuals with the disease (T2D). Introduction: Beyond the hereditary factor, there are several risk factors associated with the development of this syndrome; the lifestyle plays an increasingly predominant role in the development of the metabolic complications related to T2D and a significant role in the onset of this syndrome is played by an unbalanced diet. Polyphenolic food is a plant-based food, including vegetables, fruits, whole grains, tea, coffee, and nuts. In recent years, there has been growing evidence that polyphenols, due to their biological properties, may be used as nutraceuticals and supplementary treatments for various aspects of T2D. Polyphenols may influence glycemia and T2D through hypoglycemic properties, such as reduced insulin resistance, reduced fasting blood glucose, and glycosylated hemoglobin value. Based on several in vitro, animal models, and some human studies, it has been detected that polyphenol-rich products modulate carbohydrate and lipid metabolism, attenuate hyperglycemia, dyslipidemia, and insulin resistance, improve adipose tissue metabolism, and alleviate oxidative stress and stress-sensitive signaling pathways and inflammatory processes. Methods: This manuscript summarizes human clinical trials conducted within the last 5 years linking dietary polyphenols to T2D, with a focus on polyphenolic foods found in the Mediterranean diet. Results: Intaking polyphenols and their food sources have demonstrated beneficial effects on insulin resistance and other cardiometabolic risk factors. Prospective studies have shown inverse associations between polyphenol intake and T2D. The Mediterranean diet and its key components, olive oil, nuts, and red wine, have been inversely associated with insulin resistance and T2D. Conclusion: In conclusion, the intake of polyphenols may be beneficial for both insulin resistance and T2D risk. However, other human clinical studies are needed to evaluate the suitable dose and duration of supplementation with polyphenolic food in T2D patients.