Flavonoids are plant compounds found in familiar foods such as onions, citrus fruit, berries and soya. If you have read about quercetin, catechins or anthocyanins, you have already met a few members of this family. Bioflavonoids is another name you may see for them. [2]
You do not need a cupboard full of powders to explore them. I would begin with the foods you like, then look at what the research tells us about including more variety. The names are useful when you want to learn more, but they should not make putting dinner together feel difficult.
What are flavonoids, and how do they fit into polyphenols?
Flavonoids are a large family within the wider group called polyphenols. Both sit within the broader subject of phytochemicals, compounds produced by plants. They are grouped by their chemical structures, rather than by a single health effect. [2] [8]
In plants, flavonoids have jobs including contributing colour and helping responses to environmental stresses. Anthocyanins provide many red, blue and purple pigments. Other members of the family are less obvious when you look at a food, so colour alone will not tell you everything it contains. [3] [10]
The phrase antioxidant often appears alongside flavonoids. It describes an activity that can be measured in an experiment. Human research also looks at cell signalling, inflammation and blood-vessel function. A strong result in a laboratory test does not establish that a supplement prevents illness. [8]
Which types of flavonoids are in everyday foods?
These six subgroups are commonly discussed in dietary research. A food can contain several compounds, so the examples are starting points for exploring, rather than a complete list. [1]
| Type | Examples | Where to find them |
|---|---|---|
| Flavonols | Quercetin, kaempferol, myricetin, isorhamnetin | Onions, kale, broccoli, apples and berries. |
| Flavan-3-ols, also called flavanols | Catechin, epicatechin, EGCG; linked forms include proanthocyanidins | Tea, cocoa, apples, grapes and berries. |
| Flavones | Apigenin, luteolin, chrysin | Parsley, thyme and celery provide members of this group. |
| Anthocyanins | Forms of cyanidin, delphinidin, malvidin, pelargonidin and peonidin | Red, blue and purple berries and grapes. |
| Flavanones | Hesperetin, naringenin, eriodictyol | Citrus fruit. |
| Isoflavones | Genistein, daidzein, glycitein, biochanin A | Soya beans and soya foods are useful sources. |
Examples are based on the Linus Pauling Institute's food-source reference. [1] The foods listed supply members of each group; they do not necessarily contain every example named.
Are flavonols and flavanols the same?
No. The spelling is close, but they are different subgroups. Quercetin is a flavonol. Catechin is a flavanol, also called a flavan-3-ol. That distinction helps when comparing studies: a paper on one group cannot automatically tell us what another will do. [1]
Anthocyanins and anthocyanidins are related too. Anthocyanins have sugars attached to an anthocyanidin structure. The anthocyanin guide is another route into the subject. [3]
Which other names are worth exploring?
There are more names beyond the six common dietary groups. Keeping a wider list gives you routes into the chemistry, the foods and future reading.
- Flavanonols, also called dihydroflavonols, include taxifolin. These are distinct from catechins and are studied as their own compounds. [19]
- Chalcones and related dihydrochalcones are another area of plant and medicinal chemistry. Evidence for a particular extract or medicine should not be assigned to ordinary food servings. [20]
- Aurones and phlobaphenes appear in the wider plant-pigment literature. They are useful topics if you are curious about how plants make colour, rather than extra dietary targets. [10]
A 2019 food-analysis study examined red chicory, red onion, aubergine, purple sweet potato and black carrot. Researchers identified different mixtures of anthocyanins, other flavonoids and phenolic acids. It is an interesting example of variety within vegetables, but the study measured extracts and antioxidant activity, not health outcomes in people. [4]
What does research show about blood vessels and heart health?
A six-month UK trial tested freeze-dried blueberry preparations equivalent to 150 g or 75 g of fresh blueberries daily against placebo in adults with metabolic syndrome. This means a cluster of risk factors such as raised blood pressure, central body fat and abnormal blood fats. There were 138 people randomised and 115 completed the study. [12]
The higher blueberry amount improved some measures of blood-vessel function, including how well an artery widened in response to increased blood flow. The main outcome, insulin resistance, did not improve, and blood pressure was unchanged. The study did not test whether blueberries prevented heart attacks. [12]
The authors reported:
“improved markers of vascular function and elements of lipid status.”
Curtis and colleagues, American Journal of Clinical Nutrition (2019) [12]
This gives a specific food finding to explore. It does not isolate anthocyanins from everything else in blueberries, or establish the same result for every flavonoid. I would make space for berries if you enjoy them, while keeping the rest of your meals varied.
Can flavonoids help with memory and thinking?
The research is mixed. One of the original papers linked here followed 1,779 adults in the Framingham Offspring cohort, with repeated diet assessments and cognitive tests. Over a median of 11.8 years, the researchers found some modest patterns, but no clear overall association between higher flavonoid intake and slower age-related cognitive decline. [9]
Their conclusion included:
“our findings do not support a clear association”
Shishtar and colleagues, Public Health Nutrition (2020) [9]
A different 2021 study followed 49,493 women and 27,842 men. Higher long-term flavonoid intake was associated with lower odds of reported difficulties with memory and thinking. These were participants' own reports, rather than the repeated cognitive tests used in the Framingham study. The studies asked related but different questions. [11]
Both were observational. They cannot prove that flavonoids caused a benefit, or that a supplement prevents dementia. The earlier news report is still available, with the original 2021 study now linked in Resources so you can read beyond its headline.
What happens to flavonoids after we eat them?
They change during digestion and metabolism, the processes your body uses to handle substances. Gut microbes help break down some flavonoids, producing smaller compounds called metabolites. Food structure and differences between people influence how much reaches the circulation and in what form. Cassidy and Minihane's review explains these variations. [13]
This helps explain why a milligram figure on a packet is only part of the story. The original compound, its metabolites and the person taking it all matter. A result obtained by placing a concentrated compound directly onto cells may involve exposures quite different from eating a meal. [6]
How can I include flavonoid-containing foods more often?
Look at a meal you already make and choose one addition. An onion can go into soup, herbs into a bean salad, and fruit alongside breakfast. There is no need to build a separate flavonoid menu.
- Stir berries into porridge or serve them with another breakfast you enjoy.
- Add parsley and chopped celery to a lentil salad.
- Use onions and broccoli in a stir-fry.
- Try tofu in a curry, or soya beans in a bowl of mixed vegetables.
- Use unsweetened cocoa for flavour in oats or a homemade date-based treat.
These are ideas using the food groups above, not recipes with calculated doses. I like planning a week's meals around ingredients that can appear in more than one dish. Parsley bought for a salad could also finish a soup. Batch cooking can make those choices easier on busy days.
Dr Michael Greger's NutritionFacts.org offers another way to explore flavonoids through food. Its topic page links to educational videos and research questions. I would follow the underlying studies when a particular claim catches your attention, especially if it concerns treating disease. [14]
Do I need raw, fresh or organic ingredients?
You can use cooked meals as well as fresh fruit and salads. Cooking and processing affect flavonoid content and availability in different ways, depending on the food and method. There is no single rule that makes every compound more available. [13]
Frozen and tinned fruit and vegetables can count towards your five a day. [16] That gives you options when fresh ingredients are expensive or difficult to use before they spoil. Check what you already have in the freezer before adding more to the shopping list.
Organic is my personal preference, but it should never feel like a condition of starting. Choose what you can afford and enjoy. This article is not a reason to replace familiar ingredients with expensive specialist foods.
Should I buy quercetin, catechin or other flavonoid supplements?
I would not turn findings about foods into a shopping list of isolated compounds. A supplement changes the dose and the combination of substances being consumed. The results of food studies do not establish that an extract will produce the same outcome. [13]
Concentrated products also need their own safety assessment. For example, uncommon liver injuries have been reported with green tea products, mainly extracts in capsules or tablets. Green tea can interact with some medicines. Ask a pharmacist about a product if you take medication. [15]
Can quercetin help with hay fever?
There is some promising human research on supplements. In a 2022 trial, 66 Japanese adults with pollen-allergy symptoms took a specific quercetin formulation or placebo for four weeks. The supplement supplied 200 mg of quercetin daily, and some scores for sneezing, a runny nose, itchy eyes and quality of life improved compared with placebo. This was a small, short study of a formulation designed to improve absorption. [21]
An earlier trial in 24 people tested enzymatically modified isoquercitrin, a quercetin-related supplement, for eight weeks around the Japanese cedar pollen season. Eye symptom and medication scores improved, while nasal symptoms did not differ significantly. [22]
A 2025 review brought together 13 trials of different polyphenolic preparations in 823 people with allergic rhinitis, which includes hay fever. It found improvements in some nasal symptoms, but rated the certainty of key findings low to very low. Quality-of-life effects were not significant overall. [23]
I would describe this as encouraging research that needs stronger confirmation. These studies tested supplements, so they cannot tell us that eating more onions or apples will relieve hay fever, or establish a benefit for every quercetin product. If symptoms are troubling you, ask a pharmacist about suitable treatment and whether a supplement fits with any medicines you take.
A few more practical questions
Is there a daily flavonoid target?
There is no established dietary requirement for flavonoids as a group. [17] I would focus on the balance and variety of your food, rather than trying to reach a number taken from one study. The balanced plant-based diet guide can help with the wider plan.
Should I drink more green tea?
Tea supplies flavan-3-ols, but you can include that group through other foods too. [1] If you like it, the green tea and matcha article is a related topic. That older guide still awaits the same review as this page.
If iron is a concern, tea and coffee can reduce absorption when taken with meals. The Vegan Society suggests drinking them outside meal times and including vitamin C with iron-containing foods. [18] You can find practical combinations in the iron guide.
Where can I explore the earlier research?
The older papers offer several routes into the subject. Gardana and colleagues analysed flavonoids and furanocoumarins in bergamot juice; this was a composition study, not a treatment trial. Moon and colleagues reviewed enzymes involved in processing medicines and other substances. The citrus review by Benavente-García and Castillo explores proposed biological actions, while the broader reviews cover chemical structure and mechanisms. [5] [6] [7] [8]
Hichri and colleagues' plant-science review looks at how flavonoid production is regulated. It is a different question from whether a supplement improves health, and a useful starting point if you are interested in plants themselves. [10]
