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Table of Contents
Introduction
Polyphenols are a group of naturally occurring compounds found abundantly in plants. They are characterized by having multiple phenolic rings and are known for their antioxidant properties. They also have numerous additional health benefits. They can reduce inflammation, improve heart health, and lower the risk of certain diseases including cancer, neurodegenerative diseases, and type 2 diabetes.
Such a list of benefits leads to just one conclusion: a healthy diet should contain plenty of polyphenols. But do you know whether your diet is rich in polyphenols? And should you worry if you don’t know anything about them?
Well, all you need to do is read on. I’m giving you a complete overview of these remarkable molecules, which you’ll want to fill your plate with.
Polyphenols: A complex family of plant-derived molecules
Overview of the main groups
The main polyphenol groups are the flavonoids, the largest and most studied group of polyphenols, the phenolic acids, the stilbenes, the lignans and the tannins.
The flavonoids are further divided into several subclasses, including flavonols (e.g., quercetin, kaempferol), flavones (e.g., apigenin, luteolin), flavanones (e.g., naringenin, hesperetin), flavanols (e.g., catechins, epicatechins), anthocyanidins (e.g., cyanidin, delphinidin), and isoflavones (e.g., genistein, daidzein). Flavonoids are widely distributed in fruits, vegetables, tea, cocoa, and wine.
Phenolic acids are divided into two main groups: hydroxybenzoic acids (e.g., gallic acid, vanillic acid) and hydroxycinnamic acids (e.g., ferulic acid, caffeic acid). They are found in various plant-based foods, including fruits, vegetables, whole grains, and coffee.
Stilbenes are a class of polyphenols known for their role in plant defence mechanisms. The most well-known stilbene is resveratrol, which is found in grapes, berries, and wine.
Lignans are polyphenols found primarily in seeds, whole grains, and flaxseeds. They are converted by gut bacteria into enterolignans, such as enterodiol and enterolactone, which have potential health benefits.
Tannins are a diverse group of polyphenols known for their astringent taste. They can be further classified into hydrolyzable tannins (e.g., ellagitannins, gallotannins) and condensed tannins (proanthocyanidins). Tannins are found in various plant-based foods, including tea, coffee, fruits, and nuts.
If this is already too complex for you, you might not want to know that these are just some of the main polyphenol families. There are many other subclasses and individual compounds within each family around.
For the sake of simplicity, I will focus on just a few of them in the remainder of this article. You won’t need to remember all those barbaric names anyway.
Polyphenols known for their health benefits
Quercetin is a flavonoid found in many fruits and vegetables, such as apples, onions, and berries. It has antioxidant and anti-inflammatory properties and has been studied for its potential to improve heart health, reduce blood pressure, support immune function, and protect against certain chronic diseases.
Catechins are a type of flavonoid found in tea, particularly green tea. They are known for their potent antioxidant activity. Catechins, such as epigallocatechin gallate (EGCG), have been associated with various health benefits, including cardiovascular protection, weight management, and potential anticancer effects.
Curcumin is the main polyphenol present in turmeric, a spice commonly used in curry dishes. It has powerful anti-inflammatory and antioxidant properties and has been studied for its potential in managing chronic conditions such as arthritis, metabolic syndrome, and certain types of cancer.
Anthocyanins are a group of pigments responsible for the vibrant colours in many fruits and vegetables, such as berries, cherries, and purple sweet potatoes. They have been linked to improved cardiovascular health, anti-cancer effects, and potential cognitive benefits.
Ellagic acid is a polyphenol found in various fruits, including strawberries, raspberries, and pomegranates. It has been studied for its potential anticancer properties, particularly in relation to its antioxidant and anti-inflammatory effects.
Genistein is an isoflavone found in soybeans and soy products. It acts as a phytoestrogen and has been studied for its potential in reducing the risk of hormone-related cancers, improving bone health, and managing menopausal symptoms.
Health benefits of a polyphenol rich diet
Antioxidant effects
Polyphenols are powerful antioxidants that can help protect the body from oxidative stress and damage caused by free radicals.
Oxidative stress has been linked to numerous health problems, including heart disease, cancer, and neurodegenerative diseases. It refers to an imbalance between the production of free radicals and the ability of the body’s antioxidant defences to neutralize them. Free radicals are highly reactive molecules that contain an unpaired electron. They are formed as natural by-products of cellular metabolism and can also be generated by external factors such as pollution, radiation, and certain drugs.
When free radicals are produced in excessive amounts or if the antioxidant defence system is compromised, they can cause damage to various cellular components. Antioxidants can neutralize free radicals by donating an electron or by scavenging them directly. Some antioxidants are produced within the body, while others, including polyphenols, are obtained from the diet.
Improved heart health
Polyphenols have been shown to have numerous benefits for heart and cardiovascular health, including reducing blood pressure, improving blood lipid levels, and reducing the risk of blood clots. For example, a study found that resveratrol, a type of polyphenol found in red wine, improved heart health by reducing inflammation, improving blood lipid levels, and reducing the risk of heart disease.
They have been shown to reduce blood pressure by several mechanisms. One way is by improving endothelial function, which is the ability of blood vessels to dilate in response to increased blood flow. This is thought to be due to the ability of polyphenols to increase the production of nitric oxide, a molecule that promotes vasodilation. Polyphenols can also inhibit the production of vasoconstrictive hormones, such as angiotensin II, which can increase blood pressure.
Polyphenols can improve blood lipid levels by reducing the oxidation of low-density lipoprotein (LDL) cholesterol, also known as “bad” cholesterol. When LDL cholesterol becomes oxidized, it can contribute to the development of atherosclerosis, a condition in which plaque builds up in the arteries, leading to a narrowing of the blood vessels and an increased risk of heart disease. They can also increase the production of high-density lipoprotein (HDL) cholesterol, also known as “good” cholesterol, which helps to remove LDL cholesterol from the bloodstream.
Polyphenols can reduce the risk of blood clots by inhibiting platelet aggregation, which is the process by which blood cells clump together to form a clot. This is thought to be due to the ability of polyphenols to modulate several signalling pathways and enzymes involved in platelet activation, including cyclooxygenase (COX) and phospholipase A2 (PLA2).
At the molecular level, polyphenols can exert their beneficial effects on cardiovascular health by interacting with several signalling pathways and enzymes involved in blood pressure regulation, lipid metabolism, and blood clotting. For example, they can activate the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, which is a transcription factor that regulates the expression of antioxidant and detoxification enzymes. Polyphenols can also inhibit the activity of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, which is a transcription factor that promotes inflammation and oxidative stress. By modulating these pathways and enzymes, polyphenols can reduce oxidative stress, inflammation, and the risk of cardiovascular disease.
Lowered risk of numerous diseases
Polyphenols have been linked to a reduced risk of certain diseases, including cancer, neurodegenerative diseases, and type 2 diabetes.
They have been shown to reduce the risk of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease, by several mechanisms. Polyphenols can reduce oxidative stress and inflammation in the brain, which are thought to be major contributors to the development and progression of these diseases. Polyphenols can also modulate several signalling pathways involved in neuronal survival, including the PI3K/Akt pathway, the extracellular signal-regulated kinase (ERK) pathway, and the c-Jun N-terminal kinase (JNK) pathway.
Regarding reducing the risk of type 2 diabetes, polyphenols can improve insulin sensitivity, which is the ability of cells to respond to insulin and take up glucose from the bloodstream. They can also reduce inflammation and oxidative stress in the pancreas, which is the organ that produces insulin. Additionally, these molecules can modulate several signalling pathways involved in glucose and lipid metabolism, including the AMP-activated protein kinase (AMPK) pathway, the peroxisome proliferator-activated receptor gamma (PPARγ) pathway, and the sirtuin 1 (SIRT1) pathway.
Polyphenols have been studied for their potential anti-cancer properties. One way is by inhibiting the growth and proliferation of cancer cells. Polyphenols can also induce apoptosis, which is programmed cell death, in cancer cells. Additionally, they can modulate several signalling pathways involved in cell growth, differentiation, and survival, including the mitogen-activated protein kinase (MAPK) pathway, the phosphatidylinositol 3-kinase (PI3K)/Akt pathway, and the nuclear factor-kappa B (NF-κB) pathway.
Skin Health and UV Protection
Some polyphenols, such as those found in green tea and cocoa, have been shown to offer protective effects against ultraviolet (UV) radiation from the sun. Research suggests that these polyphenols can help reduce inflammation and oxidative damage caused by UV exposure, potentially contributing to improved skin health and protection against sunburn and premature aging.
Gut Health and Polyphenol Metabolism
Polyphenols can also interact with the gut microbiota, the complex community of microorganisms in the digestive system. This interaction can lead to the production of metabolites with potential health benefits. For example, studies have shown that certain polyphenols, like those found in red wine or berries, can be metabolized by gut bacteria to produce compounds that have anti-inflammatory and antioxidant properties, potentially promoting gut health and overall well-being.
Resveratrol: The longevity molecule?
Found in grapes, red wine, and certain berries, resveratrol has attracted significant attention due to its potential role in promoting longevity and overall health. While there is compelling evidence from laboratory studies and animal research that this molecule promotes longevity, unfortunately, the evidence from human studies is still limited and inconclusive.
Resveratrol has been shown to activate certain enzymes, such as sirtuins, which are involved in regulating cellular processes related to aging and lifespan. Studies conducted on various organisms like yeast, worms, and flies have demonstrated that resveratrol can extend lifespan and improve health span. These findings suggest that resveratrol may have anti-aging effects.
Numerous animal studies have also reported positive effects of resveratrol on lifespan and health span. For example, mice fed a high-calorie diet along with resveratrol showed improved metabolic health and extended lifespan compared to mice on the same diet without resveratrol. Similar results have been observed in other animal models as well, including fish and primates.
Human studies investigating the effects of resveratrol on longevity are limited and have produced mixed results. Some studies have shown potential benefits, while others have not found significant effects. A few small-scale studies have suggested that resveratrol supplementation may improve markers of cardiovascular health and metabolic function, which are associated with longevity. However, it’s important to note that these studies are short-term and focused on surrogate markers rather than direct measurement of lifespan.
Resveratrol’s potential link to longevity is often associated with the “Blue Zones,” which are regions around the world where people live significantly longer and healthier lives. These regions include places like Okinawa (Japan), Sardinia (Italy), and Ikaria (Greece), among others. Some researchers have hypothesized that the consumption of resveratrol-rich foods, such as red wine in moderation, may contribute to the health and longevity observed in these populations. However, other lifestyle factors, overall dietary patterns, and genetics likely play a more significant role in the longevity observed in these regions.
Polyphenols Anti-inflammatory effects: The example of Quercetin
Polyphenols have been shown to have anti-inflammatory effects by reducing the production of pro-inflammatory molecules in the body.
For example, quercetin, a type of polyphenol found in apples and onions, reduced inflammation and oxidative stress in people with rheumatoid arthritis. The molecular mechanisms by which quercetin reduces inflammation have been studied extensively.
First, Quercetin can inhibit the activity of enzymes such as cyclooxygenase (COX) and lipoxygenase (LOX), which are involved in the production of pro-inflammatory molecules called prostaglandins and leukotrienes, respectively. It can also suppress the production of pro-inflammatory cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), which play a key role in the inflammatory response.
Moreover, Quercetin is a potent antioxidant and can scavenge free radicals that contribute to oxidative stress and inflammation.
Finally, this flavonoid can modulate signalling pathways involved in inflammation, such as the nuclear factor-kappa B (NF-kB) and mitogen-activated protein kinase (MAPK) pathways.
Should we worry about deficiencies in polyphenols?
General considerations
You don’t need to worry specifically about including polyphenol-rich foods in their diet. By adopting a diverse and balanced diet that includes a variety of fruits, vegetables, whole grains, legumes, nuts, and seeds, individuals can naturally obtain a good intake of polyphenols without needing to track or measure them specifically.
Polyphenols are widely distributed in plant-based foods, and by consuming a range of fruits and vegetables with different colours and types, individuals can ensure they are getting a variety of polyphenols. The key is to focus on overall dietary patterns rather than fixating on individual compounds.
Tips to ensure an adequate intake of polyphenols
Aim to include fruits and vegetables of various colours in your daily meals. Different colours often indicate different polyphenol profiles, so by consuming a diverse range, you’ll likely be getting a variety of polyphenols.
Choose Whole Foods over processed ones whenever possible. Whole fruits, vegetables, whole grains, legumes, nuts, and seeds are excellent sources of polyphenols.
Herbs and spices, such as oregano, thyme, cinnamon, and cloves, are often rich in polyphenols. Incorporating these flavours into your cooking can provide additional polyphenol benefits.
Tea, especially green and black tea are rich in catechins, and coffee in chlorogenic acid, a molecule with antioxidant and anti-inflammatory properties.
Berries, such as blueberries, strawberries, raspberries, and blackberries, are particularly rich in polyphenols, particularly anthocyanins. They can be a great addition to your diet.
Finally, I should indicate that Dark chocolate contains flavanols, a type of polyphenol, that have been shown to improve heart health and, as mentioned several times already, red wine is high in resveratrol, which has been linked to numerous health benefits.
Polyphenols properties overlap
By focusing on a varied and plant-rich diet, individuals can naturally obtain a good range of polyphenols without needing to worry about specific quantities or individual compounds. It’s important to emphasize overall dietary patterns and lifestyle factors that support good health rather than fixating on any single nutrient or compound.
Different foods can contain varying types and concentrations of polyphenols. For example, resveratrol is commonly associated with red grapes and red wine. While it can also be found in other fruits like blueberries and cranberries, the highest concentrations are typically found in the skin of red grapes.
However, there is no evidence to suggest that individuals who do not consume wine or resveratrol-rich berries, or any specific polyphenol-rich food, are at a significant disadvantage or will be deficient in polyphenols.
Different types of polyphenols have overlapping and complementary effects, and their combined presence in a balanced diet is more important than consuming a specific polyphenol-rich food. The synergistic interactions between different polyphenols and other compounds found in plant foods contribute to their overall health-promoting effects.
Specific dietary considerations
Some individuals have allergies or intolerances to specific foods, including those rich in polyphenols. For example, certain fruits or berries may trigger allergic reactions or intolerances
Polyphenols, like other compounds in food, can interact with certain medications. For instance, some polyphenols may inhibit or enhance the effects of specific medications, affecting their efficacy or safety.
Certain health conditions may require tailored dietary recommendations. For instance, individuals with kidney disease may need to monitor their intake of certain polyphenols found in foods like tea, nuts, and berries due to their potassium or oxalate content. Similarly, individuals with gastrointestinal conditions may need guidance on consuming polyphenol-rich foods that could exacerbate symptoms.
While polyphenols offer potential health benefits, they should not overshadow the importance of obtaining a balanced intake of essential nutrients. Individuals with specific nutrient deficiencies, such as iron or vitamin C, may need to focus on food sources that provide those nutrients in addition to polyphenols.
These are just a few examples, and individual circumstances may vary. It’s always prudent to seek personalized advice from professionals who can provide tailored recommendations based on your specific health needs, dietary preferences, and potential interactions or restrictions.
Conclusion
The consequences of not consuming a diet rich in polyphenols can vary depending on an individual’s overall dietary pattern and other lifestyle factors. While polyphenols have been associated with potential health benefits, it is difficult to attribute specific health outcomes solely to the absence of polyphenol-rich foods.
The impact on an individual’s health is influenced by numerous factors, including overall dietary quality, nutrient intake, physical activity levels, genetics, and other lifestyle factors. A diet lacking in polyphenol-rich foods may potentially lead to a lower intake of certain beneficial compounds.
For example, the absence of fruits, vegetables, whole grains, and other plant-based foods may result in reduced consumption of various polyphenols, along with other essential vitamins, minerals, and dietary fibres found in these foods. This could potentially contribute to an increased risk of certain chronic diseases, including cardiovascular diseases, certain cancers, and age-related neurodegenerative conditions.
The overall dietary pattern, including the intake of various nutrients and bioactive compounds, plays a significant role in health outcomes. A diet lacking in polyphenols can still be nutritionally adequate if it includes a wide range of other nutrient-dense foods. Conversely, consuming polyphenol-rich foods alone may not compensate for an otherwise poor diet.