If I had to dedicate an article for every single chemical, compound or component of food that has some kind of benefit for humans, I would have endless topics to write about. I prefer to devote time to enlighten readers on what I find to be the significant components, or in other words, the ones that have the most profound or broad range of benefits. I’d like to review a group of compounds that don’t receive the publicity they deserve, besides in scientific journals, which most of us don’t peruse. Every time you take a bite out of that delicious apple you had saved for a snack, or munch down on your olive oil-sprinkled Greek salad, you are unknowingly ingesting a host of beneficial chemicals.

Polyphenols are a group of phytochemicals (“Phyto” refers to plant) that are second to carbohydrates in abundance in higher plants and are also secondary metabolites involved in hydrogen peroxide scavenging in plant cells, hence why polyphenols are prized for their anti-inflammatory activity but also possess immunomodulatory and antimicrobial properties (Sun & Sharahbajabian, 2023). Over 8000 phenolic compounds have been identified but only a select number of them have been studied for their therapeutic benefits. Here is a list of the major polyphenols within their two groups, flavonoids and non-flavonoids and food sources of each type;

Flavonoids	Non-flavonoids
Flavonols (cocoa, dark chocolate, berries, apple, nuts) Quercetin Kaempferol Isorhamnetin Ruthin Myricetin	Stilbenes (grapes, wine) Resveratrol
Flavanones (citrus fruits) Naringenin Hesperidin Naringin Eriodyctiol Silybin	Phenolic acids (spices and herbs, coffee, tea, wine, cocoa) Ferulic acid Coumaric acid Syringic acid  Vanillic acid Caffeic acid
Isoflavones (soybeans) Genistein Daidzen Glycitein Flavones (apple skins, berries, parsley, thyme, celery) Apigenin Luteolin Tangeritin
Flavan-3-ols (apricots, sour cherries, grapes, blackberries) Epicatechin gallate  Catechins
Anthocyanins (black elderberry, black chokeberry, black currant, red wine, coloured legumes) Delphinidin Malvidin Peonidin Cyanidin Petunidin (Di Lorenzo et al, 2021) & (Tanwar & Modgil, 2012)

Rather than focus on benefits of each of the major polyphenols found in food sources, I will elucidate how polyphenols have been shown to improve health outcomes and reduce mortality risk in the three most prevalent chronic diseases, cardiovascular disease, cancer and diabetes.

Cardiovascular disease

There is an inverse correlation between coronary disease and ingestion of flavanols, flavanones, flavones, and anthocyanins, highlighting that polyphenol consumption reduces mortality risk (Abbas et al, 2017). Polyphenols exert their cardiovascular benefits through a variety of mechanisms;

• Reduction in inflammatory markers involved in CVD pathophysiology, including vascular cell adhesion molecule, intercellular adhesion molecule, interleukins, tumour necrosis factor alpha, and monocyte chemotactic protein (Durazzo et al, 2019)
• Decreasing cardiac levels of reactive oxygen species (ROS) and malondialdehyde (MDA), a metabolite that forms when ROS and oxidized LDL attack fatty acids in cell membranes 
• Improving the production and bioavailability of nitric oxide (NO) (a compound that is critical for vasodilation) by sequestering ROS that destroy NO 
• Induces antioxidant enzymes, such as superoxide dismutase, catalase, and glutathione peroxidase in cardiovascular tissue
• Reduce oxidative stress by inhibiting cyclooxygenase (COX) and lipoxygenase (LPO), enzymes that are involved in prostaglandin synthesis (a process necessary for inflammation) (Quiñones et al, 2012)

Diabetes

Epidemiological studies elucidate that diets high in phenolic compound intake have a moderate risk reduction against developing type 2 diabetes. Additionally, diets rich in phenolic compounds from decaffeinated green tea, coffee, dark chocolate, blueberry jam, extra-virgin olive oil, and polyphenol-rich vegetables (artichokes, onions, spinach, and rocket) have been shown to reduce plasma glucose by increasing insulin sensitivity and secretion. As polyphenols are metabolized by flora in the large intestine, it has been shown that some of the by-products of polyphenol fermentation (isovanillic acid and 3-o-sulfate) can stimulate glucose uptake into muscle tissue (Fernandes et al, 2022). 

Certain polyphenols have been directly studied for their effects on managing and preventing diabetes; 

Curcumin

• enhances the secretion of adiponectin, a hormone that controls glucose uptake and lipid metabolism 
• regulating pathways that control the growth and proliferation of adipocytes, suppressing lipid accumulation and adipogenesis (fat cell synthesis)
• improve insulin resistance and hyperglycemia
• reduce lipid oxidation, free fatty acid, triglyceride, cholesterol, and blood glucose levels 

Resveratrol

• increases pancreatic -cell function by inhibiting phosphodiesterases (PDEs), which degrade cyclic adenosine monophosphate levels (cAMP)
• increases intracellular cAMP, a compound necessary for glucose and insulin secretion, as well as pancreatic function (Aryaeian et al, 2017)

Cancer

Polyphenols exert their anti-cancer effects by influencing carcinogenesis and tumour development at the cellular level by modulating the activity of key proteins involved in the control of cell cycle progression and influencing the expression of genes associated with cancer. For example, epigallocatechin gallate (EGCG), a polyphenol found in green tea, has been shown to induce apoptosis and inhibit cancer cell growth by changing the expression of proteins signalling, cell cycle regulatory proteins and activity involved in cell growth, transformation, and metastasis (Abbas et al, 2016). Additionally, phenolic compounds act on carcinogenesis throughout the induction of cell defence systems, including detoxifying and antioxidant enzyme systems, as well as the inhibition of the anti-inflammatory and anti-cellular growth signalling pathways that culminate in cell cycle arrest or death. Other polyphenols, such as apigenin, resveratrol, genistein, luteolin and quercetin have also been shown to induce the apoptosis of several malignant cells (Briguglio et al, 2020).  

As the title states, think of polyphenols as the guerrilla in your fruits and vegetables, waiting to help your body tackle any stress it encounters. Considering that we are exposed to innumerable sources of stress, from electromagnetic frequencies all the way to additives in the water we drink, it pays to have tools at our disposal to mitigate this constant pressure. Who would’ve thought that the apple you take to work every day or the Greek salad you had for yesterday’s dinner could have precisely what you need to prevent stress from having insidious effects on your system. 

References

Abbas, M., Saeed, F., Anjum, F.M., Afzaal, M., et al. (2018). Natural polyphenols: an overview. Internationaljournal of food properties, 20(8), 1689-1699. https://doi.org/10.1080/10942912.2016.1220393  

Aryaeian, N., Sedehi, S.K. & Arablou, T. (2017). Polyphenols and their effects on diabetes management: A review. Medical journal of the Islamic republic of Iran, 31, 134. https://doi.org/10.14196%2Fmjiri.31.134

Briguglio, G., Costa, C., Pollicino, M., Giambo, F., et al. (2020). Polyphenols in cancer prevention: new insights (review). International journal of functional nutrition, 1(2). https://www.researchgate.net/profile/Giusi-Briguglio/publication/345348220_Polyphenols_in_cancer_preventionnew_insightreview/links/5fa48df392851cc28698d7b2/Polyphenols-in-cancer-preventionnew-insightreview.pdf

Durazzo, A., Lucarini, M., Souto, E.B, Cicala, C., et al. Polyphenols: A concise overview on the chemistry, occurrence, and human health. Phytotherapy research, 33(9), 2221-2243. https://doi.org/10.1002/ptr.6419

Di Lorenzo, C., Colombo, F., Biella, S., Stockley, C., et al. (2021). Polyphenols and human health: the role of bioavailability. Nutrients, 13(1), 273. https://doi.org/10.3390%2Fnu13010273

Fernandes, I., Oliveira, J., Pinho, A. & Carvalho, E. (2022). The role of nutraceutical containing polyphenols in diabetes prevention. Metabolites, 12(2), 184. https://doi.org/10.3390/metabo12020184

Quiñones, M., Miguel, M. & Aleixandre, A. (2012). Beneficial effects of polyphenols on cardiovascular disease. Pharmacological research, 68(1), 125-131. https://doi.org/10.1016/j.phrs.2012.10.018

Sun, W. & Shahrajabian, M.H. (2023). Therapeutic potential of phenolic compounds in medicinal plants-natural health products for human health. Molecules, 28(4), 1845. https://doi.org/10.3390%2Fmolecules28041845

Tanwar, B. & Modgil, R. (2012). Flavonoids: dietary occurrence and health benefits. Spatula DD, 2(1), 59-68. https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=546c605f00237b0aa75170585ea172c51e7b9513