An Overview of Dietary Polyphenols and Their Therapeutic Effects

Abstract Polyphenols are a diverse class of natural antioxidants found mostly in fruits and vegetables. Epidemiological studies show that long-term exposure to polyphenol-rich dietary supplements demonstrates reduced cellular oxidative stress. These secondary metabolites have been found to hold cellular protective properties against diseases such as cancer, cardiovascular diseases, diabetes, and neurodegenerative diseases. An estimate of 8000 polyphenolic compounds has been identified from myriad sources such as fruits, vegetables, cereals, and beverages (red wine and green tea) and extensively studied for their medicinal properties. For the various classifications of these compounds, dietary intake and their bioavailability are altered depending on their chemical structures. The bioavailability of phenolic compounds determines their biological properties, so understanding the bioavailability of various phenolic compounds will aid in understanding their role in disease prevention. The absorption of these compounds holds a genetic predisposition; as a result, different ethnic groups have been identified to have discrete absorption levels of these compounds. In addition, epigenetic changes in DNA, such as DNA hypomethylation, play a role in carcinogenesis, but dietary polyphenols, such as (−)-epigallocatechin 3-gallate (EGCG) from green tea and genistein from soybean, have exhibited mechanisms such as inhibition of DNA methyltransferases (DNMT). This further enhances the role of polyphenols as protective agents in diseases such as cancer. Thus, incorporation of an individualized polyphenolic diet dependent on the type of disease would provide an improvised therapeutic approach towards polyphenols. This review, therefore, focuses on the different aspects of polyphenols and their role in disease prevention.