What are phytochemicals & why do we need them?

Phytochemicals immune system


What are phytochemicals?

Phytochemicals, also sometimes referred to as phytonutrients or polyphenols (these are actually a subclass of phytochemicals) are biologically active compounds of plant origin. These bioactive chemicals are a plants natural pesticides that it uses to protect from predators.  Normally the noxious properties of phytochemicals are activated by damage to the plant e.g. eating or chopping and are liberated to dissuade insects and pests from eating them. 

Natural plants have been used to prevent and to treat various diseases for thousands of years and these properties are now attributed to the abundance of phytochemicals.  Currently they are not established nutrients (deemed non-nutrive) – meaning we don’t have a specific recommended daily intake or reference amount for deemed necessary for health – this is in part because they are not essential to survive as say vitamins & minerals.  Lifestyle factors can act as a guide. If you smoke or live in a heavily polluted area, deal with high stress or high risk of infection you need them even more to help your body quash and protect against infection and free radicals that are attacking your cells.

Also, probably due to lack of understanding of their properties and clear proof regarding how a lack of a phytochemicals in the diet affects health.  Science has only just begun to scratch the surface, but in the last few years there is a significant body of evidence supporting their significant contribution to protection against disease.  And herein lies the beauty of plants over pills – drugs used to treat a disease after it’s developed, is like quenching chaos after it’s evident, dig a well when in thirsty, or casting a sword in a battle — It is treating the symptoms somewhat too late?

At present a large number of phytochemicals have been identified (literally 8000+).  They are broadly classified as Carotenoids & Polyphenols but there are many further subdivisions.  It’s not just all the various colourful fruits and veggies but also beans & pulses, tea, coffee, red wine, cacao, herbs, spices, condiments & olive oil.  See end of document for some specific examples.

Harness plant-powered medicine

Numerous studies support the health-giving properties of these compounds.  They impact our bodies in numerous & surprising ways: protecting our DNA from damage, acting as anti-oxidants, regulating hormonal function, boosting immune function and possessing anti-microbial properties.  They can even potentially destroy cancer-forming cells.  They play a crucial role in both your chronic inflammatory disease (e.g. non-infectious disease/lifestyle disease) risk and your ability to fight off colds and infections.  A 2013 study published in the Journal of Nutrition found a link between high polyphenol consumption and a 30 percent decrease in mortality in elderly adults.

Whole food synergy

The general message is to take advantage of the huge health potential of phytochemicals and eat more of them and a diverse selection.  Rather than taking a multi-vitamin/mineral supplement (which lacks inclusion of these powerful phytochemicals), by eating a diverse plant rich diet you will also ensure that you have many of your micronutrient needs covered (vitamin and minerals) but also be getting plenty of gut loving fibre to nurture the microbiome – these gut resident good bacteria are actually helping us liberate these phytochemicals from the food we eat.  Recent study showed greatest diversity in people eating >30g fibre/day and consuming over 30 different plant foods per week.  It is important to understand many foods have complex mixtures of different kinds of polyphenols and that not all polyphenols have identical effects, so variety is key.

Why not take a phytochemical pill?

Although some attempts have been made to harness the benefits of phytochemicals in supplements.  Phytochemicals can be easily degraded by certain processing techniques and studies looking at the quality have found huge variations in bioavailability.  Sometimes the method of extraction used may influence the nature of the compounds ingested and thus the safety of the product.

Phytochemicals are broad and varied.  Some are more readily absorbed (bioavailable) and utilized by the human body than others. This bioavailability often depends on other components found in in our meal.  E.g. When we eat turmeric, our liver does a great job of getting rid of the active phytochemical curcumin before our body can harness the benefits.  But if you consume turmeric with black pepper and eaten with a fat source, this significantly boosts bioavailability by up to 2000%.

In addition to these properties, some phytochemicals are so powerful that they can influence our response to drugs e.g. grapefruit & statin medication – powerful stuff!  Some supplement manufacturers recommend intakes far higher than those currently associated with the diet.  There have been numerous cases of liver toxicity in people taking some supplements without a break such as garlic or green tea supplements.  Much study is needed to determine the risks of phytochemical supplements, which may include carcinogenic effects, thyroid toxicity, interactions with prescription medications, antinutritional effects and hormone-like activity.  Do not attempt to self-prescribe but obtaining via a varied diet is a safe way to incorporate them into your diet. Plus taking a pill you miss out on all the whole food benefits: vitamins, minerals and fibre.


Want to live long and prosper? Simply eat a plant-heavy diet, which ups your phytochemical ante significantly. Overall, polyphenols appear to offer many promising health benefits both in fending off infection and in protection from chronic diseases including cancer, heart disease, obesity/metabolic disease/type 2 diabetes & neurodegenration. More research is needed before polyphenols can be recommended in supplemental doses.  For now, it is best to consume polyphenols in their natural form of plant foods.

Some examples of key phytochemicals with clinical evidence to feed ourselves well include:

  • Allicin in garlic. You may have heard that garlic is anti bacterial and for centuried has been usewd as both a food and medicine. This potent onion relative contains the active ingredient allicin, which fights infection and bacteria. British researchers gave 146 people either a placebo or a garlic extract for 12 weeks; the garlic takers were two-thirds less likely to catch a cold. Other studies suggest that garlic lovers who chow more than six cloves a week have a 30% lower rate of colon cancer and a 50% lower rate of stomach cancer.  But the way garlic is processed can really change its effects.  To optimise, use the ‘hack and hold’ technique – whereby crushing fresh garlic and letting it stand before cooking allows enzymatic conversion of alliin to beneficial allicin, the main active ingredient

  • Carotenes give produce its orange colours. Many of the immune-enhancing effects of carotenes, as well as other antioxidants, are due to their ability to protect the thymus gland from damage. The thymus is the major gland of our immune system and starts to decline from age 20! Carotenes have been shown to enhance the function of several types of white blood cells (our immune cells), as well as increase the antiviral and anticancer properties of our own immune system mediators, such as interferon

  • Sulforaphane is an isothiocyante stored inside plants, mainly cruciferous veggies in the inactive form glucoraphanin.  This is activated by the enzyme myrosinase (conveniently also found in broccoli) to release the bioactive sulforaphane.   Although myrosinase is somewhat heat sensitive, gentle heating is actually useful in aiding this chemical reaction.  Another super sulforaphane hack is to sprout your own broccoli seeds as these have way more sulphoraphane as the final plant.  Tanins (found in tea), in particular EGCG (Epigallocatechin gallate) synergises with sulforaphane in Broccoli to enhance effects.

  • Rosmarinic acid is a natural antioxidant found in culinary spice and medicinal herbs such as lemon balm, peppermint, sage, thyme, oregano, and rosemary to treat numerous ailments. 

  • Curcumin in turmeric is responsible for the yellow colour of turmeric.  There is now extensive research on its solid anti-inflammatory and anti-oxidant properties.  Although much of the research is on curcumin, one of the active ingredients in turmeric but there are over 300 compounds in turmeric and curcumin-free turmeric was also clinically effective so stick to the whole root if you choose to use it.  Turmeric is also a good inhibitor to viral entry into our cells.  So adding this spice regularly to meals could be useful to ward off infections. 

  • Anthocyanins (red, purple, and/or blue plant pigments) found in many fruits but can actually prevent the adhesion of pathogens to cell walls.  In fact, when compared to other berries, the photochemical bioavailability was much higher in cranberry juice as compared to other fruit juices which is thought to be one reason it helps prevent adhesion of pathogenic bacteria in the urinary tract.

  • Capsaicin which makes pepper spicy helps protect DNA from carcinogens. Resveratrol in grapes/grape skins.  Lycopene in tomatoes – enhanced by the cooking process.  Lutein in spinach.  Naringenin in grapefruit.