How Do Polyphenol-Rich Foods Prevent Oxidative Stress and Maintain Gut Health?

Abstract

Inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis, involves chronic inflammatory disorders of the digestive tract. Oxidative stress, associated with increased reactive oxygen species generation, is a major risk factor for IBD pathogenesis. Industrialized lifestyles expose us to a variety of factors that contribute to deteriorating gut health, especially for IBD patients. Many alternative therapeutic strategies have been developed against oxidative stress along with conventional therapy to alleviate IBD pathogenesis. Polyphenol-rich foods have attracted growing interest from scientists due to their antioxidant properties. Polyphenols are natural compounds found in plants, fruits, vegetables, and nuts that exhibit antioxidant properties and protect the body from oxidative damage. This review presents an overview of polyphenol benefits and describes the different types of polyphenols. It also discusses polyphenols' role in inhibiting oxidative stress and fungal growth prevention. Overall, this review highlights how a healthy and balanced diet and avoiding the industrialized lifestyles of our modern society can minimize oxidative stress damage and protect against pathogen infections. It also highlights how polyphenol-rich foods play an important role in protecting against oxidative stress and fungal growth.

Keywords: fungal growth; healthy diet; inflammatory bowel disease; microbiota; oxidative stress; polyphenol; reactive oxygen species generation.

Figure 1

Oxidative stress can be defined as an imbalance caused by excessive reactive oxygen species production by cells that exceeds the body’s capacity to neutralize them. Free radicals and peroxides damage intracellular structures such as proteins, lipids, and DNA and disrupt intrinsic cell mechanisms. These free radicals can be induced by exogenous factors such as smoking, air pollution, processed foods, chronic stress, UV radiation, X-rays, heavy metals (e.g., nickel, cobalt, and mercury) or by endogenous factors like intracellular mitochondria, phagocytes, endoplasmic reticulum, inflammation, gut dysbiosis, and fungal overgrowth in the gut.

Figure 2

Oxidative stress inhibitors for IBD. Along with conventional therapy, many alternative therapeutic strategies have been developed to alleviate IBD pathogenesis. Various options for reducing oxidative stress in IBD include antioxidants such as melatonin or LOX and NOX inhibitors. In addition, lifestyle modifications by consuming foods rich in fruits and vegetables and medicinal plants rich in β-carotene (pro-vitamin A), vitamin C, vitamin E, minerals, omega-3 polyunsaturated fatty acids, and polyphenols and engaging in regular exercise in combination with foods abundant in probiotics and prebiotics, can reduce oxidative stress and inflammation. Some foods (e.g., olive oil) increase antioxidant enzyme activities (CAT, SOD, and GPx). In addition, camel milk contains lactoferrin and antioxidants (bioactive peptides and vitamin C), which protect against oxidative stress in IBD patients.

Figure 3

Polyphenols and their representative food sources. Polyphenols are classified into different groups such as flavonoids, phenolic acids, tannins, stilbenes, and lignans.

Figure 4

An overview of polyphenol-rich foods and their potential effects on human health in association with gut microbiota. Polyphenols are compounds found in a wide variety of foods, including vegetables (e.g., artichoke heart, parsley, broccoli, celery, onion, garlic, lettuce, leek, zucchini, green bell pepper, tomato, cauliflower, etc.), fruits (e.g., blueberries, strawberries, raspberries, blackberries, cranberries, grapes, cherries, apricots, apples, pomegranates, oranges, grapefruits, etc.), cereals (e.g., wheat, rice, corn, rye, oat, etc.), grain legumes (e.g., beans, chickpeas, lentils, etc.), nuts (e.g., chestnuts, hazelnuts, pecan nuts, almonds, etc.), tea, coffee, dark chocolate, cocoa powder, and spices (e.g., curcuma or turmeric). For IBD patients in remission, it is important to reintroduce gradually restricted foods and drinks (vegetables, fruits, cereals, grain legumes, etc.) that contribute to a balanced diet in line with the “Eatwell Guide”. Polyphenols are mostly complex structures. Approximately 5–10% of food polyphenols are absorbed by the small intestine, while the majority (90–95%) reach the colon. They are then metabolized by the gut microbiota into absorbable simple phenolic compounds (e.g., urolithin, protocatechuic acid, etc.). Dietary phenolic compounds and their aromatic metabolites reinforce the gut microbiota through their prebiotic properties.

Figure 5

Polyphenols‘ antioxidant properties are mediated by four major mechanisms. Polyphenols can remove ROS directly, while a second action can be attributed to their ability to increase endogenous antioxidant-synthesizing enzymes. Catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD) are the most important antioxidant enzymes in cells. SOD and CAT are enzymes that catalyze the breakdown of superoxide and hydrogen peroxide, while GPx is an enzyme that catalyzes the reduction of hydrogen peroxide. As a third action, polyphenols prevent ROS formation by directly acting as metal ion chelators against transition metal ions such as copper (Cu), zinc (Zn), and iron (Fe) that play a critical role in the progression of different diseases including Alzheimer’s disease. For the fourth action, the polyphenol inhibits several enzymes involved in ROS formation (iNOS, NOX, and LOX). For example, the superoxide anion radical (O₂^.−) is produced by members of the NADPH oxidase (NOX) enzyme family, while resveratrol treatment inhibits Nox1 expression and ROS production in macrophages.

Figure 6

Effect of some representative polyphenol-rich foods on C. albicans growth inhibition. Food and spices rich in polyphenols that inhibit C. albicans growth include curcumin (curcuminoids), black pepper (p-hydroxybenzoic acid), cinnamon (proanthocyanidins), oolong tea or green tea (e.g., catechins), yarrow, St. John’s wort, oregano, thyme (carvacrol and thymol), coffee (phenolic acids), parsley (flavonoids), garlic (phenolic acids and flavonoids), onions (anthocyanins and flavonols), honey (flavonoids), cherries (procyanidins and quercetin), grapes (resveratrol), citrus fruits (naringin), pomegranates (caffeic acid, gallic acid, and epigallocatechin), and olives (hydroxytyrosol).