The red of a tomato, the purple of a berry and some of the compounds in a cup of tea are examples of the chemistry that makes plant foods interesting. Phytochemicals are compounds produced by plants. You may also see them called phytonutrients, especially when people discuss their possible effects on health. [1] [2] [3]
You do not need to remember their names to include them in your food. A varied plant-based diet brings many compounds together. Evidence is stronger for the foods and overall diet than for the benefits of isolated phytochemicals. [1]
This is a part of food I enjoy thinking about: what else could go into a salad, which vegetables would work in a soup, or how to use something different from the shopping basket. I would begin with that curiosity and the meals you already like.
What is the difference between phytochemicals and phytonutrients?
The terms overlap in everyday nutrition writing. Phytochemical describes a chemical made by a plant; phytonutrient is often used to emphasise a possible nutritional or health role. The Linus Pauling Institute defines phytochemicals, in the broadest sense, as:
“chemicals produced by plants”
Linus Pauling Institute, Oregon State University [1]
In health research, the term generally refers to plant compounds beyond essential nutrients. They should not all be treated like vitamins with established daily requirements. [1] There are exceptions to a neat dividing line: some carotenoids, including beta-carotene, can be converted into vitamin A by your body. [3]
If a name sounds complicated, look for the food it belongs to. Learning that an apple contains flavonoids can be interesting. You can still enjoy the apple without learning the chemistry first.
Which plant foods contain phytochemicals?
They occur across plant foods, including fruit, vegetables, pulses, whole grains, nuts and tea. [1] The compounds fall into overlapping families. Flavonoids are part of the larger polyphenol group; anthocyanins and isoflavones sit within the flavonoid family. [2]
There are many more types to explore than a short list can show. Some names describe a broad family and others a single compound inside it. The explanations include established roles in plants, biological actions studied in people, and promising laboratory findings. These are different kinds of evidence.
Broad families
| Group or compound | Where it comes from | What it does, or what research is exploring |
|---|---|---|
| Polyphenols | Fruit, vegetables, tea, cocoa and other plant foods | A broad family containing flavonoids and compounds such as resveratrol. Researchers study their effects on cell signalling and other processes; there is no single effect shared equally by every polyphenol. [2] [18] |
| Flavonoids and bioflavonoids | Apples, onions, citrus fruit and tea | Bioflavonoids is another name commonly used for flavonoids. In plants, members of this family help with pigmentation and responses to environmental stresses. Human research examines signalling and vascular effects. [2] |
| Anthocyanins and anthocyanidins | Red, blue and purple berries and grapes | Contribute red, blue and purple pigments. Anthocyanins are sugar-linked forms of anthocyanidins. Their biological actions are being studied; colour alone does not establish a health benefit. [2] |
| Proanthocyanidins | Apples, berries, cocoa and grape seeds | Linked chains of flavonoid units. Grape-seed extracts have been studied for blood pressure and cholesterol, with small, varied trials. Those findings cannot simply be assigned to every food containing them. [2] [25] |
| Carotenoids | Carrots, tomatoes, spinach and kale | Plant pigments including beta-carotene, lycopene and lutein. Some can supply vitamin A after conversion; others cannot. Lutein and zeaxanthin are present in the retina of the eye. [3] |
| Glucosinolates | Broccoli, cabbage, kale and Brussels sprouts | Break down into compounds including isothiocyanates. These are studied for effects on enzymes and cellular responses to stress. Food studies and laboratory mechanisms do not establish cancer treatment. [4] |
| Allium compounds, including organosulfur compounds and sulfides | Garlic and related allium vegetables | Crushing garlic allows enzymes to turn alliin into allicin, which can form other sulfur compounds. Research on garlic preparations includes cardiovascular risk factors, with results depending on the preparation. [12] |
| Phytoestrogens, including isoflavones | Soya foods; lignan-containing foods such as flaxseed | Some compounds or their metabolites can interact with estrogen receptors. Their effects depend on the compound and tissue; describing them as universal hormone balancers would be misleading. [14] [13] |
Individual compounds and food-based topics
| Group or compound | Where it comes from | What it does, or what research is exploring |
|---|---|---|
| Lignans | Flaxseed, sesame seeds, whole grains and other plants | Gut bacteria can convert plant lignans into enterolignans, which have weak estrogenic activity. The contribution of lignans themselves to disease prevention is still being investigated. [13] |
| Sulforaphane | Formed from glucoraphanin in broccoli and some other cruciferous vegetables | An isothiocyanate studied for effects on enzymes involved in handling foreign chemicals and cellular stress. This is more specific than saying broccoli flushes out toxins. [4] |
| Chlorophyll | Green leaves and algae | The green pigment captures light for photosynthesis. Chlorophyll supplements and chlorophyllin are different products; the plant role does not establish a general human detox effect. [15] |
| Curcumin | Turmeric | A yellow pigment studied for inflammatory pathways. Early human evidence on some turmeric/curcumin products and knee-osteoarthritis symptoms is encouraging, but stronger evidence is needed. Culinary turmeric is not the same as a tested extract. [16] |
| Ellagic acid | Raspberries, strawberries, pomegranates and walnuts | Shows antioxidant and other biological activity in laboratory work. It is an interesting research topic, but there is no evidence supporting its use as a cancer treatment. [17] |
| Resveratrol | Grape skins, peanuts and some berries | Studied for cell signalling, stress responses and ageing mechanisms. Laboratory and animal lifespan findings do not demonstrate that supplements make humans live longer. [18] |
| Capsaicin | Chilli peppers | Responsible for chilli heat. Topical capsaicin medicines act on pain-related nerve cells and can relieve some muscle and joint pain. Eating chilli is not equivalent to applying a medicine. [19] |
| Astaxanthin | Certain microalgae, including Haematococcus pluvialis | A pink-red carotenoid pigment. Included here because algal pigments are often discussed alongside plant compounds. EFSA has assessed supplement safety; that assessment does not establish a general health benefit. [20] |
| Phytosterols | Nuts, seeds, grains and other plant foods; some enriched foods | Plant sterols and stanols reduce intestinal cholesterol absorption. LDL reduction is best established for suitable enriched products at studied amounts, rather than an unspecified serving of any plant food. [26] |
Plant extracts and specialist research topics
These were part of my wider list too. They offer further things to learn about, although they are not all everyday food ingredients or reasons to buy a supplement.
| Group or compound | Where it comes from | What it does, or what research is exploring |
|---|---|---|
| Boswellic acids | Boswellia resin, also known as frankincense | Preclinical work examines enzymes involved in inflammation. Small studies of Boswellia extracts suggest possible help with osteoarthritis symptoms, but the evidence needs better trials. Resin extracts are different from ordinary foods. [22] [21] |
| Coumarins | A family including coumarin, found in Cassia cinnamon and other plants | Coumarin contributes fragrance and flavour. It is not a nutrient to maximise: substantial ongoing exposure can harm the liver in susceptible people. Ceylon cinnamon generally contains much less coumarin than Cassia. [23] |
| Dithiolethiones | Naturally occurring and synthetic compounds discussed in specialist research | Studied for increasing the activity of phase 2 enzymes, which help process foreign chemicals. Much work concerns experimental agents and animal models; this is not an established dietary treatment. [24] |
Antioxidants describe an activity rather than a separate phytochemical family. The section below explains that distinction; the antioxidants and free radicals article is another route into the topic.
Some linked guides are older and still await the same evidence review as this overview. The sources beside each summary above support the explanation given here.
Is eating the rainbow useful?
Colour can be a helpful reminder to vary your fruit and vegetables. Some plant pigments, such as anthocyanins and carotenoids, contribute to those colours. Green leaves can contain carotenoids too, even when their yellow or orange pigments are less obvious. [2] [3]
It is a prompt, rather than a score for how healthy your dinner is. Pale foods have a place: onions contain flavonoids, and whole grains and beans belong in a varied plant-focused diet. [2] [10] A plate does not need every colour at every meal.
I would think across the week. If your usual soup has carrots, perhaps add another vegetable you enjoy. If breakfast is always the same fruit, try a different one when it suits your budget. Familiar favourites can stay while you explore.
What does research actually tell us?
A 2017 systematic review by Aune and colleagues brought together 95 prospective studies, which followed people over time. Higher fruit and vegetable intake was associated with lower risks of cardiovascular disease and death from any cause; the association with total cancer was smaller. [5]
These were observational findings. They cannot establish that one phytochemical caused the difference, and other habits or imperfect dietary reporting may affect the results. They support interest in fruit and vegetables as foods, rather than prove that a capsule containing one of their compounds will have the same effect. [5]
What is a dietary phytochemical index?
Researchers have also explored ways to estimate how much of a person's diet comes from phytochemical-rich foods. In a small study published in 2010, Vincent and colleagues used a dietary phytochemical index based on the proportion of food energy coming from those foods. Among 54 young adults, the index was related to measures of body fat and oxidative stress, but not to the cytokines measured, which are immune-signalling proteins. [27]
This was a cross-sectional study, meaning it compared diet and health measures without assigning people a diet to follow. It cannot show that phytochemicals caused the differences or give you a daily amount to aim for. I find the food question more useful in the kitchen: could you add beans to your soup, another vegetable to dinner or some berries to breakfast? [27]
Where does cancer-prevention advice fit?
The World Cancer Research Fund recommends making whole grains, vegetables, fruit and pulses a major part of the usual diet. Its evidence review identifies strong evidence for whole grains and foods containing fibre reducing colorectal cancer risk. Evidence varies for other food and cancer combinations. [10]
Reducing risk is different from guaranteeing prevention or treating an existing illness. A particular vegetable cannot be promised to prevent cancer, and a laboratory result showing an effect on cancer cells does not establish that eating that food treats cancer in a person. [4] [6]
A plant-based perspective from Dr Michael Greger
NutritionFacts.org, Dr Greger's educational organisation, discusses phytonutrients through everyday foods and makes the point:
“the whole is often greater than the sum of its parts”
NutritionFacts.org, Phytonutrients [7]
I would use that as a reminder to look at the whole food, then check the evidence behind a specific health claim. The topic page introduces research questions; it is not itself a clinical trial. The studies and evidence reviews linked here help distinguish promising ideas from demonstrated outcomes.
Are all phytochemicals antioxidants?
No. Antioxidant describes an activity, rather than one family of plant compounds. Antioxidants interact with free radicals, reactive chemicals that can damage cells. Some phytochemicals show antioxidant activity, while researchers also study other actions, including effects on cell signalling. [6] [2]
Activity measured in a test tube does not tell you how much of a compound reaches tissues after digestion or whether it prevents disease. Flavonoids, for example, are changed during absorption and metabolism, so the substances circulating in your body may differ from those originally in the food. [2]
I would avoid choosing a food simply because its packaging advertises a very high antioxidant score. It is more useful to ask whether you enjoy it, how it fits into your meals and what evidence supports the claim being made.
Does cooking destroy phytochemicals?
Cooking can change them in different ways. It is too simple to say raw is always better. In a laboratory study, Dewanto and colleagues heated tomatoes and found increased bioaccessible lycopene and measured antioxidant activity, while vitamin C decreased. Bioaccessible means available to be released from the food during digestion. [8]
This was a food-analysis study, not a trial showing that cooked tomatoes prevent disease. The practical lesson is that cooking can involve trade-offs, rather than removing all nutritional value. [8] A tomato sauce can have a place alongside a fresh tomato salad.
I would choose a mixture of preparations you enjoy. A warm vegetable soup in winter and a colourful salad in summer can both fit. Follow safe preparation instructions, and do not let worry about the perfect method stop you using the ingredients you have.
How can I include more variety without making cooking difficult?
Start with a meal you already make. You could add beans and another vegetable to a soup, serve a curry with different vegetables, or put a handful of berries over porridge. These are food ideas to adapt, rather than recipes with calculated amounts of phytochemicals.
Planning helps me turn an idea into dinner. Choose an ingredient, decide which meal it will go into and add it to the shopping list. If you buy a cabbage, plan where the rest might go as well, perhaps into soup or another cooked dish.
- Breakfast: try a different fruit with your oats.
- Lunch: add cooked pulses or another vegetable to a familiar dish.
- Dinner: use a mixture of vegetables in a stew or curry.
- Flavour: experiment with herbs or spices you already have.
Keep enough substantial food in the meal too. Variety is one part of eating well; energy, protein and essential nutrients still need attention. The balanced plant-based diet guide explains how to bring those needs together.
Do I need phytochemical supplements or greens powders?
A concentrated extract should not be assumed to reproduce the benefits of the food it came from. Antioxidant supplement trials have not consistently shown cancer-prevention benefits, and some have found harm. [6]
For example, the ATBC randomised trial followed 29,133 male smokers aged 50 to 69 in Finland. Participants receiving beta-carotene supplements had a higher incidence of lung cancer than those not receiving beta-carotene. This was a supplement study in a specific population, not evidence that eating carrots causes the same harm. [11]
If a powder claims to replace vegetables, ask what was actually tested: that product, that dose and a meaningful health outcome, or simply an ingredient in a laboratory? If you take medicines or are receiving cancer treatment, discuss concentrated supplements with your healthcare team before using them. [6]
This is separate from using a supplement for an identified nutrient need. The B12 guide covers reliable B12 sources on a fully plant-based diet. Choosing food for its phytochemicals does not replace that planning.
Does everything need to be fresh or organic?
No. Frozen and tinned fruit and vegetables can count towards your five a day, as can vegetables cooked into meals. Choose tinned options in water or natural juice, without added sugar or salt where available. [9] You do not need a basket of fresh produce every day to make a useful change.
I personally choose organic when it suits me, but I would not want the cost to put you off eating more plants. Use what you can afford and will enjoy cooking. A few dependable cupboard and freezer ingredients may make more sense for your week than lots of unfamiliar fresh food.
A few more practical questions
Do I need to calculate a daily phytochemical target?
There is no single daily target that covers this whole collection of compounds. The category includes many substances with different properties. [1] Focus on a varied diet and practical food guidance, rather than trying to add up an undefined total.
Does a superfood provide everything?
I would keep your choices broad. No single ingredient has to carry the whole diet, and you do not need expensive powders to try another vegetable, pulse or whole grain. Choose one addition you would enjoy this week and give it a place in a meal.
