They’re colourful, they protect your body from disease, and your gut microbiome loves them too: this is your science-based guide to polyphenols.
In this article, you'll discover why polyphenols are so crucial for the body, and how gut bacteria are instrumental in this relationship. We'll also tell you what foods you can find them in, and why colourful plants are the best.
Table of contents
- What are polyphenols?
- Types of polyphenols in foods
- Polyphenols prevent diseases
- Your microbiome is involved
- Mental health and polyphenols
- Eat the rainbow for health
- Colourful foods and benefits
It’s well known that a diet rich in fruits and vegetables is associated with lower disease risks. The foods that nature provides are exactly that - natural. They have no added chemicals and haven’t undergone any processing.
These plant foods are perfect for the human body to thrive on. They taste great, are full of colour, and what’s more, they have many health benefits. These benefits are provided by the nutrients and natural chemicals they contain, one example is polyphenols.
Polyphenols have antioxidant and anti-inflammatory benefits that help prevent illnesses and diseases associated with inflammation. Collectively, these beneficial properties of polyphenols are great for your health, your microbiome, and your wellbeing.
What are Polyphenols?
Polyphenols are natural compounds found in many plant-based foods and are great for your health.
Polyphenols are micronutrients present in many plant-based foods and beverages. They have antioxidant properties, so they may play a role in preventing many common diseases associated with oxidative stress.
Oxidative stress occurs in the body when large numbers of free radicals overwhelm the body’s natural repair systems. Free radicals are oxygen-containing molecules that have an uneven number of electrons.
This makes them unstable, so they hunt for an electron to pair with their odd one. That's why free radicals easily react with other molecules, leading to oxidation. Oxidative damage is a major cause of many chronic illnesses.
Antioxidants work by donating an electron to the free radical. This donation makes the free radical less reactive, but the antioxidant itself remains stable. When this system isn’t working properly, your body is more prone to certain illnesses.
Polyphenols are the most abundant antioxidant in the human body, and they come from plant foods. Hundreds of polyphenols have been identified in foods. There are two main types: flavonoids and phenolic acids, of which your recommended dietary intake is approximately one gram per day.
☝TIP☝ It may not sound like much but one gram of polyphenols is ten times more than the required amount of vitamin C, and 100 times greater than that of vitamin E!
Different types of polyphenol and their food sources
There are many different types of polyphenols, and they aren't fancy. You can find them in the fresh produce section of the supermarket.
Polyphenols are responsible for some of the bright and vibrant colours of fruits and vegetables. Eating polyphenol rich foods is like eating (and tasting) the rainbow.
|Polyphenol class||Specific type||Food sources|
|Flavonoids||catechin, quercetin, hesperetin, cyanidin, daidzein, proanthocyanidins||onion, tea, apples, citrus fruits, red fruits, soybeans, grapes, cocoa, red wine|
|Phenolic acids||caffeic acid, ferulic acid||fruits, vegetables, whole grains, cereals, coffee|
|Phenolic amides||capsaicinoids, avenanthramides||Chilli peppers, oats|
|Other polyphenols||resveratrol, ellagic acid, lignans||Grapes, red wine, strawberries, raspberries, flax, sesame seeds and grains|
Plus, there’s a little pot of gold at the end of this nutritious rainbow, because polyphenols are good for your health and gut microbiome too.
How do polyphenols prevent disease?
You may never spare them a thought, but polyphenols are in many foods. They help to protect your body against many chronic diseases.
Cardiovascular disease is the number one cause of death worldwide, according to the World Health Organisation. Yet, most incidences of cardiovascular disease can be prevented by changing certain behaviours such as poor diet, physical inactivity, smoking, and alcohol consumption.
What’s this got to do with polyphenols? Well, you should think of polyphenols as your friend, if you want to reduce your risk of developing cardiovascular disease. It’s already a well-known fact that eating a diet rich in fruit, vegetables, whole grains, and other sources of dietary fibre is great for your health.
Tea is a well-known sources of polyphenols, but they're in foods too
A major cause of heart disease is an elevated level of low-density lipoprotein (LDL), or as it’s more commonly known, bad cholesterol. Large quantities of LDL circulating in your blood can lead to a build-up of fatty deposits on your arteries.
These fatty deposits reduce the flow of blood around your body and increase the risk of heart attacks and strokes. The build-up of fat in your arteries is a condition called atherosclerosis. However, polyphenols can limit the development of these fatty deposits.
When free radical activity goes unchecked by antioxidants, they interfere with LDL. This triggers a series of inflammatory responses resulting in atherosclerosis. The consumption of polyphenols and their antioxidant effects means they can help protect you from atherosclerosis.
Equally, polyphenols like those found in red wine have been shown to prevent the formation of blood clots, in animal studies. And, drinking tea and a moderate consumption of wine may lower the risk of heart attacks.
Type II diabetes
Just like cardiovascular disease, type 2 diabetes mellitus is a significant health burden and one which is, again, preventable. There is significant evidence pointing towards polyphenols and their ability to help prevent the disease.
Dietary flavonoids are particularly important in the fight against diabetes. That’s because they not only have anti-inflammatory effects, but they improve both glucose (sugar) and lipid (fat) metabolism.
A meta-analysis carried out by Xu et al found that the risk of developing diabetes type II was reduced when there is a high intake of flavonoids. Thus, flavonoid-rich foods seem to have an anti-diabetic effect.
So, we know polyphenols have anti-inflammatory and antioxidant effects, which must mean they can help prevent cancer, too, right? Exactly. In fact, scientists have increased their attention on polyphenols since it was found they can alter cancer cell growth.
You’ve already heard it, a diet high in fruits and vegetables reduces the risk of many cancers, and we already know they are rich in polyphenols. Polyphenols have many mechanisms to help prevent cancer.
Polyphenols are involved in regulating the biological processes involved in cancer initiation. They can also stop tumor cells from even growing in the first place. And, they even have a way to make tumor cells kill themselves, a process known as apoptosis.
Gut microbiota and polyphenols
The polyphenols in plant foods aren't just popular with your body, they support the growth of beneficial bacteria in the gut too.
It’s fair to say polyphenols are gutsy micronutrients: they navigate your body, pair up with free radicals, and ultimately protect you from chronic illness. But it doesn’t just stop there, they're also involved with your gut microbiota.
Up to 95% of the polyphenols you eat travel (undigested) to the colon where they are broken down into smaller metabolites. Gut bacteria like Lactobacillus, Bifidobacteria, and Escherichia coli have all been identified as catalysts in the metabolism of polyphenols.
Colour is the trademark sign of polyphenols in whole foods
This is a two-way relationship. In return for being transformed into bioavailable metabolites (suitable for use by your body), dietary polyphenols promote the growth of beneficial bacteria and prevent that of opportunistic bacteria.
The mutual relationship shared between polyphenols and gut microbiota is thought to contribute to your health. Some studies have shown that polyphenols promote the growth of probiotic bacteria like Bifidobacterium and Lactobacillus.
Polyphenols are considered prebiotics because they feed the Bifidobacteria in your gut. Therefore, they increase the population of the bacteria, promoting the health of your gut. The antioxidant properties of some polyphenols also make them promising candidates for the treatment of inflammatory gut diseases.
Another bacterial species which has a special relationship with polyphenols is Akkermansia muciniphila. This beneficial microbe accounts for up to 4% of your intestinal bacteria and is associated with lean body mass and obesity prevention.
Certain polyphenols could have a positive effect on Akkermansia muciniphila. For example, polyphenols from grapes can increase the abundance of this bacterial species which increase the function of the intestinal barrier.
☝FACT☝Some polyphenols can prevent bacterial growth, but they are usually absorbed in the small intestine and don't make to the colon where they could disturb your microbiome.
Polyphenols and mental health
Polyphenols regulate the composition of your gut bacteria, and this can have serious consequences for your brain and mood.
Your gut-brain axis is two-way communication between your gastrointestinal tract and your central nervous system. It has an important role in your stress response, and your gut microbiota can act upon your nervous, hormonal and immune system to influence your brain function.
If the gut-brain axis is destabilised (dysbiosis), then it can have knock-on effects for neurological disorders and neurodegenerative diseases. However, polyphenols could have a protective role via their ability to regulate the composition of your gut microbiota.
These phytochemicals have the potential to improve depression because of their anti-inflammatory and antioxidant effects. Oxidative stress is a major factor in the development of psychiatric disorders, and cells in the central nervous system are sensitive to the damaging effects of free radicals.
Eat the rainbow of polyphenols
They look great, they taste even better, and at the same time, the polyphenols in the fruit and veg you eat help protect you from illness.
If you want to be physically and psychologically healthy, you need to eat plenty of fruits and vegetables. It’s as simple as that. The plethora of phytonutrients they contain, like polyphenols, vitamins, minerals and fibre, are essential for your body.
The problem is, many of us eat well below the recommended intakes and yet, there is so much evidence out there detailing the benefits of plant-based foods. In fact, it’s so bad that there is a phytonutrient gap, meaning 80% of American adults aren’t eating enough phytonutrients of every colour.
Most of us forget that food can be prepared and cooked in different ways to give variety. For example, raw, steamed, boiled, blended, and mashed are all ways you can prepare the fruit and vegetable for your meal. And, don’t forget to season, too, to bring out extra flavours!
Our table below highlights different foods according to their colours. Each of these colours are associated with different health benefits and can help you to incorporate each of them into your daily diet. That way, you’ll be sure to be getting the polyphenols your body needs to reduce the risk of chronic disease, as well as keep your gut healthy and happy.
Colourful foods and their benefits
|Red||apples cherries, redcurrants, raspberries, strawberries, tomatoes, red onion||anthocyanins, flavonoids, phenolic acids, tannins||anti-inflammatory, antioxidant activity|
|Yellow||lemons, golden delicious apples, bananas, yellow onions, yellow bell peppers||bioflavonoids,hesperidin, rutin, naringenin, nobiletin||protects against stomach ulcers, helps regulate blood sugar levels|
|Orange||apricots, oranges (fruit), peaches, carrots, blood oranges, nectarines, yukon potatoes, turmeric||flavanols, phenolic acids, hesperidin, circuminoids||anti-inflammatory, antioxidant activity, cardioprotective|
|Green||spinach, swiss chard, green tea, olives, celery, asparagus, green apples||flavonoids, epigallocatechin gallate, isoflavones, tannins, vitexin||anti-inflammatory, antioxidant activity, cardioprotective|
|Blue||blueberries, grapes, blackberries, prunes, raisins, plums||flavonoids, procyanidins, flavanols, phenolic acids, stilbenes||antioxidant activity, cancer prevention, lowers cholesterol, improves mood and cognitive function|
Polyphenols are present in so many fruits, vegetables, and beverages, but you might not have been aware you were even consuming them. They give food their distinctive colours and they are renowned for their antioxidant and anti-inflammatory benefits.
They even have a bi-directional relationship with your gut microbiota. In return for your gut bacteria making them available to your body, polyphenols have a prebiotic effect on some of the beneficial bacteria in your gut.
Their ability to help prevent many chronic and degenerative diseases has increased scientists’ interest in polyphenols. They are a fundamental part of your diet. The colours of the fruit and vegetables can be linked to the health benefits, and by ‘eating the rainbow’, you can benefit from these effects.
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- Cardona, F et al. (2013). Benefits of Polyphenols on Gut Microbiota and Implications in Human Health. The Journal of Nutritional Biochemistry: 24(8), pp 1415-1422.
- Duda-Chodak, A. (2012). The Inhibitory Effect of Polyphenols on Human Gut Microbiota. Journal of Physiology and Pharmacology: 63(5), pp 497-503.
- Filosa, S et al. (2018). Polyphenols-Gut Microbiota Interplay and Brain Neuromodulation. Neural Regeneration Research: 13(12), pp 2055-2059.
- Gwiazdowska, D et al. (2015). The Impact of Polyphenols on Bifidobacterium Growth. Acta Biochimica Polonica: 62(4), pp 895-901.
- Manach, C et al. (2005). Polyphenols and Prevention of Cardiovascular Diseases. Current Opinion in Lipidology.
- Minich, D, M. (2019). A Review of the Science of Colourful, Plant-Based Food and Practical Strategies for “Eating the Rainbow”. Journal of Nutrition and Metabolism.
- Naito, Y et al. (2018). A Next-Generation Beneficial Microbe: Akkermansia muciniphila. Journal of Clinical Biochemistry and Nutrition: 63(1), pp 33-35.
- Ozdal, T et al. (2016). The Reciprocal Interactions Between Polyphenols and Gut Microbiota and Effects on Bioaccessibility. Nutrients: 8(2),
- Scalbert, A et al. (2005). Dietary Polyphenols and the Prevention of Diseases. Critical Reviews in Food Science and Nutrition: 45, pp 287-306.
- Scalbert, A et al. (2005). Polyphenols: Antioxidants and Beyond. Am J Clin Nutr :81(suppl), pp 215S-217S.
- Trebatická, J et al. (2015). Psychiatric Disorders and Polyphenols: Can They Be Helpful in Therapy? Oxidative Medicine and Cellular Longevity.
- Tsao, R. (2010). Chemistry and Biochemistry of Dietary Polyphenols. Nutrients: 2, pp 1231-1246.
- World Health Organisation. (2019). Cardiovascular Diseases.
- Xu, H et al. (2018). Flavonoids Intake and Risk of Type 2 Diabetes Mellitus. A Meta-Analysis of Prospective Cohort Studies. Medicine: 97.