• Bronwyn Kohler

Phytonutrients: the Gold at the End of the Rainbow

Updated: Jul 19

Long before there were humans to eat them, plants were waging chemical warfare. Everything from fungus to dinosaurs had leafy greens on their menu, and a plant's survival depended on making sure that it could endure the onslaught. Without the ability to run away, and only limited ability to defend themselves physically, plants turned to chemicals as their weapons of choice. They have evolved a vast array of defensive molecules known as secondary plant metabolites, which range from mildly bitter deterrents that discourage over-browsing to deadly molecules that can wipe out would-be attackers for good.

Plants can sense being touched, and change the way they grow, how they taste, and what effect they have on their predators according to how much they are being nibbled at. Plants even communicate with one another through airborne chemical messages and a complex underground fungal network coined the ‘wood-wide web’ to coordinate their defenses. A tree being browsed by a giraffe warns others down the way to pump more tannins into their leaves and become bitter, encouraging the herbivore to move on to sweeter pastures before doing too much damage. But what does all this have to do with rainbows?

Evolution is an arms race. For every defense that plants create, their attackers find new work-arounds. The herbivore that can turn a plant defense into an asset has an edge on the one that can’t stomach it, and the plant that develops a mutually beneficial synergy with its predators stays in business. Over the long journey of evolution, some herbivores evolved the ability to turn plant weapons into powerful metabolic tools. Humans have inherited many of these gifts formed over millennia of synergy with plants.

This synergy is poignantly demonstrated by a group of plant metabolites known as Salvestrol, first discovered by cancer drug researchers Profs. Dan Burke and Gerry Potter in 2002. Human beings, even healthy ones, produce about 1000 cancerous cells per day. The question Burke and Potter asked was not ‘why do humans get cancer?’, but rather ‘why don’t humans get cancer?’. What happens to all those cancer cells in healthy people? Their drug research had revealed that when a cell’s normal function breaks down, including when it becomes cancerous, a gene called CYP1B1 is activated to produce the protein it codes for. Healthy cells do not express the gene, so CYP1B1 protein serves as a highly specific marker for damaged cells. Burke and Potter discovered that resveratrol, a plant metabolite found in the skins of grapes and berries, could transform CYP1B1 into an enzyme that triggered cell death. This meant that CYP1B1 was effectively a plant-triggered cancer suicide gene. Soon many more plant metabolites with the same effect were added to the list, and the duo coined them Salvestrols.

So which plants contain these magic chemical bullets? Resveratrol, which is also a potent antioxidant, antiviral and anti-inflammatory agent, is found in red grapes, berries, red wine, plums and tomato peels. Notice a common theme? Many of the metabolites that act as Salvestrols are also pigments, found in the skins of fruits and vegetables with bright colours and bitter flavours. Diets rich in whole, colourful fruits and vegetables therefore deliver high levels of cancer cell-killing Salvestrols. But there is a catch…

The chemicals that act as Salvestrols are produced as plant defenses to fungal, bacterial, viral and insect attacks. In the absence of such attacks, the plants don’t produce as many defensive chemicals. Intensively farmed plants, which grow protected by fungicides and insecticides in microbially depleted soils never encounter the attacks that a wild plant would, and are therefore greatly depleted of these cancer-killing metabolites. This is part of why there is great value to consuming organically-raised fruits and vegetables which have had to fend off pests naturally in microbe-rich rich soils.

Salvestrols are not the only reason to eat colourful fruit and vegetables. Dozens of different plant metabolites have become integral components of healthy human metabolism. These 'phytonutrients' can only be found in selected plant foods. Since many are pigments, it follows that different vegetable colours are associated with particular health benefits.


Red fruits and vegetables contain potent antioxidants which are associated with cellular health and protection, vascular health and prostate health. Many are rich in resveratrol and therefore cancer-protective.

Berries, red and pink fruits, beetroot, kidney beans, red potatoes, radishes, red peppers and tomatoes fall into this category.


Orange fruits and vegetables are packed with carotenoids, most notably vitamin A precursor beta-carotene. Carotenoid rich foods include squashes, orange sweet potato, carrots, melons and stone fruits. Citrus and various orange fruits are also rich in bioflavanoids and vitamin C. Together, these phytonutrients support your immune and reproductive systems, and promote vision, skin, and bone health. They help prevent runaway inflammation, defend against infection, and ward off cancer and heart disease.


Green foods, especially leafy greens, are packed with a diversity of phytonutrients, each with its own set of nutritional gifts to give. Indoles and phytoestrogens support hormone balance and liver function; phytosterols combat high cholesterol; folate is essential to neural health and chlorophyll aids detoxification. Crucifers such as broccoli contain potent glucosinolates that are protective against various cancers.


Not only do purple, blue and black fruits such as berries contain resveratrol, the powerful Salvestrol discussed above, but they also contain the potent antioxidant pterostilbene. Both compounds help to defend cells from the relentless onslaught of oxidative stress associated with modern living that underlies the emerging epidemic of chronic disease. Studies suggest that they can help to defend against cancer, regulate of inflammation, improve blood lipids and improve cognitive health.


OK, the food rainbow is a little weird, but being an unconventional colour in a rainbow does not diminish this group's nutritional value. Brown and white foods such as nuts, seeds, garlic, onions and mushrooms contain a vast array of phytonutrients. The alliums (garlic, onions and other such strong smelling bulbs) contain sulphur-rich compounds that are potently antibacterial and antiviral, as well as cancer-protective. Nuts and legumes are packed with fibre and lignans that support digestion, hormonal health, detoxification and a healthy microbiome. Best of all, both coffee and chocolate make it onto this list for their wealth of antioxidants and heart health protecting flavanoids.

Plants quite literally provide humans with the secret weapons they need to defend their health. It is possible to survive without these precious plant-based nutrients, but your health will gradually deteriorate as the assaults of oxidative stress, inflammation and toxicity wear down your aging systems. Diets rich in colourful plant foods are associated not just with longer lifespans, but also with longer health spans. Multiple studies have shown that you get to live longer, stay stronger, think clearer, and enjoy life more into your old age if you eat a colourful whole-food plant-rich diet.

So don’t just leave it to the unicorns. Claim the treasures Nature has evolved for you and

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