This article was written by Serge, MSc. Plant Biologist and Environmental Scientist with a BSc in Plant Biology and an MSc in Environmental Biology and Biogeochemistry. My background covers plant biochemistry, botany, and field research in forest and soil ecosystems. I write from real experience, not just literature.
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Plants do not make the compounds in your food for you. They make them to survive UV radiation, pest attack and oxidative stress. Every flavonoid, every carotenoid and every phenolic compound in your vegetables and herbs exists because the plant needed it first. That is the starting point for understanding phytochemicals in food.
I studied this in detail during my plant biochemistry coursework, and it changed how I read nutrition. The compounds that end up on your plate are plant defence chemistry. That they interact with human physiology at all is a coincidence of molecular shape. A useful one, but a coincidence.
Why Plants Make the Compounds That Make Food Valuable
Plants cannot move. When a pathogen attacks, when UV radiation increases or when a herbivore starts feeding, the plant cannot run. It responds biochemically.
Secondary metabolites are that response. Flavonoids, glucosinolates, terpenoids and many others serve the plant as UV screens, antimicrobials, feeding deterrents and managers of oxidative stress. I explain the logic behind this in more depth in why plants produce secondary metabolites.
What makes food interesting from a biochemistry angle is that many of these same compounds interact meaningfully with human physiology. Not because evolution designed it that way, but because we share enough basic molecular architecture with the rest of the living world that plant defence chemistry and human cell biology overlap in useful ways.
My plant ecological stress physiology training covered secondary metabolite investment as a resource allocation decision. The plant weighs the metabolic cost of producing these compounds against the survival benefit, and when stress increases, the investment increases. That decision is written into the chemistry of everything you eat.
The Compounds Worth Knowing About
Coloured fruits and vegetables get their pigmentation from flavonoids and carotenoids. Anthocyanins, a type of flavonoid, give berries their deep reds and purples. Carotenoids give carrots and tomatoes their orange and red tones.
Carotenoids are more than pigments: they are essential to photosynthesis, helping capture light and protecting the photosynthetic machinery from damage. None of these colours are decorative. They are functional compounds whose levels shift with growing conditions.
Leafy greens contain chlorophyll alongside vitamins and phenolic acids. Cruciferous vegetables like broccoli and kale (Brassica oleracea) produce glucosinolates, sulphur-containing compounds stored separately from an enzyme called myrosinase. When the tissue is damaged, the two meet and form isothiocyanates, such as sulforaphane in broccoli, which are the biologically active breakdown products. That is exactly what happens when you chew them.
Alliums like garlic (Allium sativum) and onion (Allium cepa) produce organosulphur compounds through a similar damage-response mechanism. The pungent chemistry that makes your eyes water when you cut an onion is the plant’s defence system activating. The same chemistry that makes raw garlic so sharp is what makes it worth eating, as I explain in medicinal plants and their active compounds.
Herbs and spices tend to have the highest secondary metabolite concentrations of all. Turmeric (Curcuma longa), rosemary (Salvia rosmarinus) and ginger (Zingiber officinale) accumulate terpenoids and phenolic compounds in amounts that dwarf what you find in most vegetables.
Small quantities carry a lot of phytochemical density, although some, like the curcumin in turmeric, are hard for the body to absorb, as I cover in turmeric chemistry and bioavailability.
Growing Conditions Change What You Eat
This is something I think about a lot, given my background in plant stress physiology and my field research experience.
A plant grown under stress produces a different chemical profile from one grown in comfortable, optimal conditions. Low soil nutrients, water stress, high UV exposure and pest pressure all trigger secondary metabolite production as part of the plant’s defence response.
My silver birch field research showed this directly. Under elevated ozone and temperature stress, the trees shifted carbon allocation away from primary growth toward stress-response chemistry. The same principle operates in food plants.
Wild plants and traditionally grown varieties often show higher phytochemical concentrations than commercially optimised crops grown for yield, uniformity and shelf life. When you remove the stressors, the plant has less reason to produce defensive chemistry.
Soil biology plays a role too. Mycorrhizal fungi networks, microbial diversity and organic matter all influence nutrient availability and plant stress levels in ways that ripple through into the chemistry of what the plant produces above ground.
I explain how those fungal networks work in mycorrhizal fungi in garden soil, and if you want to check how alive your own soil is, my guide Soil Life Check walks you through simple tests. The connection between what happens underground and what ends up in leaves and stems is closer than most people realise.
Traditional Food Systems and Plant Chemistry
Different food traditions around the world converged independently on plant diversity as a core principle: varied coloured vegetables, fermented foods, herbs and spices used daily, and whole, unprocessed plant foods as the foundation of every meal. Fermentation itself changes plant chemistry in interesting ways, which I look at in fermenting herbs and bioavailability.
From a plant biochemistry angle, this makes complete sense. Diversity of plant species means diversity of biosynthetic pathways and compound classes. No single plant produces everything, and a varied plant-based diet covers a wider range of phytochemical profiles than a narrow one.
Traditional food cultures developed through observation over long periods rather than controlled trials. But the plant biology they were working with was real, and the patterns they identified hold up when you look at them through a plant biochemistry lens.
What This Means Practically
Eat a wide variety of plant species. Prioritise colour diversity, because pigmentation reflects phytochemical diversity. Include herbs and spices regularly, because concentration matters more than most people realise.
Choose minimally processed whole plant foods where possible, because heavy processing degrades many secondary metabolites. And vary your cooking, since some compounds survive best raw while others, like the lycopene in tomatoes, become more available when cooked with a little fat.
Growing some of your own food is one of the most direct ways to put this into practice, and my guide Your First Vegetable Garden takes you through getting started.
None of this is complicated. The biochemistry behind it is, but the practical application is not. That gap between how complex the science is and how simple the takeaway turns out to be is one of the more satisfying things about studying plant chemistry.
FAQs
Do plants produce different compounds depending on how they are grown?
Yes. Environmental stress during growth influences secondary metabolite production significantly. Plants under UV, nutrient or pest pressure accumulate higher concentrations of protective compounds like flavonoids and phenolics than plants grown in optimised, low-stress conditions.
Why do colourful fruits and vegetables contain more phytochemicals?
Plant pigmentation is largely produced by flavonoids and carotenoids, both biologically active compounds. Deeper and more varied colour generally reflects higher phytochemical diversity and concentration.
What are glucosinolates and why do cruciferous vegetables contain them?
Glucosinolates are sulphur-containing compounds produced by plants in the Brassicaceae family as feeding deterrents. When the tissue is damaged, the enzyme myrosinase converts them into isothiocyanates, such as sulforaphane, which are the biologically active breakdown products. Chewing, chopping and crushing all activate this process.
Why do herbs and spices have such high phytochemical concentrations?
Most culinary herbs and spices accumulate secondary metabolites as UV screens or antimicrobial defences. Leaves, roots, seeds and bark concentrate these compounds, which is why a small amount carries more chemical complexity than a large serving of most vegetables.
Is wild-harvested food more nutritious than cultivated food?
Not always, but wild plants often show higher secondary metabolite concentrations because they grow under more environmental stress. The difference varies considerably by species and growing environment, as I explore in wild-harvested vs cultivated herbs.
What is the phenylpropanoid pathway?
It is the main biosynthetic route plants use to produce flavonoids, lignins, many tannins and a wide range of other secondary metabolites, starting from the amino acid phenylalanine. Many of the most studied plant compounds in food science come from this pathway.
Do cooking methods affect phytochemical content?
Yes, in both directions. Heat, water and processing affect each compound class differently. Volatile compounds and some vitamins are often best preserved raw or lightly cooked, while others, such as lycopene in tomatoes and carotenoids in carrots, become more available to the body when cooked, especially with a little fat.
Why do traditional food systems emphasise plant diversity?
Different plant species produce different secondary metabolite profiles through different biosynthetic pathways. Eating a wide range of plant species covers a broader range of compound classes than eating the same few plants repeatedly.
