flavonoids

Foods Richest in flavonoids

No food chart data available.

About flavonoids

Basic description

Flavonoids are a group of phytonutrients that fall into the chemical category of polyphenols. They are responsible for many of the pigments in plant foods, from the deep blues of blueberries (anthocyanins) to the pale yellows of onion skins (quercetin glycosides). The name derives from the Latin word flavus, meaning “yellow.” As a group, flavonoids are highly bioactive, functioning in UV protection, pathogen defense, and pollinator attraction in plants, while exerting antioxidant and anti-inflammatory effects in human physiology.

Over 6,000 unique flavonoids have been identified. Plant foods provide far greater quantities than animal foods, with vegetables and fruits being the most concentrated dietary sources.

Some well-studied flavonoids are known independently of any single food source (quercetin, for example). Others are closely identified with specific foods: catechins in green tea, tangeretin in tangerines and other citrus. The chemical diversity within this family is staggering.

Flavonoids are studied primarily for their antioxidant and anti-inflammatory activities, along with cardiovascular and nervous system effects. Their intake has been associated with decreased risk of certain cancers, including lung and breast cancer, though the dose required for such benefits remains uncertain and research findings conflict on several points. More details appear in the Role in Health Support section.

The Summary of Food Sources section provides additional information about flavonoids in specific foods.

Role in health support

Antioxidant benefits

Because many flavonoids,and especially those belonging to two flavonoid subgroups called flavonols and flavan-3-ols,can be effective in reducing free radical damage to cells and other components in body tissue, they provide antioxidant benefits. It is not clear, however, if flavonoids should be considered in the same category as vitamin C or vitamin E.

One reason for this is because their concentration in the bloodstream is so much lower. Another reason lies in the fact that many of the antioxidant functions of the flavonoids are not performed by the flavonoids themselves, but by forms of the flavonoids that have been altered by human metabolism. Even though the full details are not known about the way flavonoids function as antioxidants, however, studies have documented better protection of certain cell types,for example, red blood cells,following consumption of flavonoid-rich foods. Blueberries, for example, have been repeatedly studied in this context for their flavonoid-related antioxidant benefits.

In this antioxidant context, it is also worth pointing out the potentially unique relationship between flavonoids and vitamin C. Recent studies have shown the ability of flavonoids to alter transport of vitamin C, as well as to alter function of an enzyme called ascorbate oxidase, which converts vitamin C into a non-vitamin form (monodehydroascorbate). The full significance of these interactions is not yet understood, but the transport and cycling of vitamin C is flavonoid related. This association is logical, since many foods high in vitamin C ( papaya, bell peppers, broccoli, Brussels sprouts, and strawberries) are also high in flavonoids.

Anti-inflammatory benefits

Much of the research on flavonoids as anti-inflammatories has involved their ability to block the production of messaging molecules that promote inflammation. In metabolic terms, this activity of flavonoids involves the inhibition of cyclo-oxygenase (COX) and lipoxygenase (LOX) enzymes. Not only have specific flavonoids (for example, quercetin) been shown to provide these benefits but so also have flavonoid-containing extracts from a variety of foods, spices, and herbs. In addition to the metabolic activities described above, food flavonoids have also been shown to suppress inflammatory signaling in another metabolic pathway called the nuclear factor kappa-B (NF-kB) pathway.

Cardiovascular system benefits

Not surprisingly, since many problems in the cardiovascular system involve problems with oxidative stress and inflammation, the antioxidant and anti-inflammatory benefits from food flavonoids provide direct support for this body system. In the bloodstream, flavonoids have been shown to help protect LDL cholesterol molecules from oxygen-related damage. This LDL protection, in turn, helps to lower risk of atherosclerosis. Flavonoids including rutin and hesperidin have also been shown to increase the strength and integrity of the blood vessel walls, lowering risk of blood vessel problems. In one study, adding a spice mix to a meal of beef,a mix that contained such flavonoid-rich herbs as oregano, rosemary, garlic, ginger, and black pepper,led to a significant improvement in vascular function over the next several hours. Yet herbs and spices are by no means the only foods studied in this regard; similar effects have been demonstrated for soy foods, chocolate, pomegranate juice, and grape juice.

Finally, numerous flavonoids,including quercetin and rutin,have been shown to help prevent excessive clumping together of platelet cells that could otherwise lead to unwanted clogging of the blood vessels. This property of flavonoids is called an “anti-aggregatory” property, and it’s yet another way in which these phytonutrients help support the cardiovascular system.

In 2014, a research group looked at cardiovascular benefits related to the flavonoid content of fruits and vegetables. These researchers were able to determine that six total fruit and vegetable servings did a better job at protecting cardiovascular health than four total servings. They also decided upon six total servings of fruits-plus-vegetables as their minimal recommendation for heart health. The WHF daily sample menus typically include 6-10 total servings from these two food groups, exceeding this recommendation.

Support of the nervous system

Protection of nerve cells from oxygen-based damage, and help during the slow and demanding process of nerve regeneration (outside of the brain and spinal cord), are both demonstrated benefits of flavonoid intake for the nervous system. There is some preliminary evidence that the onset of certain chronic neurodegenerative diseases,including age-related dementia and Alzheimer’s disease,may be delayed when long-term intake of flavonoids has been strong.

Because flavonoids may help to improve blood flow in the brain, there is also preliminary evidence to suggest the possibility of better brain functioning in some areas, including areas involving cognitive function.

Other health benefits

In terms of their anti-cancer potential, research on flavonoids has been somewhat mixed. Due to their well-documented antioxidant and anti-inflammatory properties, flavonoids would be expected to lower risk of certain cancers since chronic oxidative stress and chronic unwanted inflammation can place cells at greater risk of becoming cancerous. Furthermore, because flavonoids are known to modify the body’s detoxification pathways, it might be expected that flavonoids would help lower exposure to unwanted toxins that could pose increased cancer risk. In studies on animals and on isolated cell types, the above expectations seem to be fully met, with flavonoid intake improving detoxification, oxidative stress, unwanted inflammation, and initiation of cells into pre-cancerous states. However, in larger scale studies on humans and risk of human cancers, greater intake of flavonoids has not been consistently associated with decreased risk of cancer. To date, the strongest evidence appears to involve breast cancer and lung cancer where decreased risk is a more consistent finding.

Part of the mixed findings in this flavonoids-and-cancer area might involve the complex nature of flavonoids as a group. For example, it may be the case that certain subgroups of flavonoids are particularly helpful for lowering risk of certain types of cancer. It might also be the case that studies have had trouble accurately quantifying flavonoid intake. There are thousands and thousands of food flavonoids, and yet some studies have only focused on very select examples or limited types of foods.

Improved detoxification is a likely benefit of consistent flavonoid intake, yet like with the area of cancer risk, research here has been somewhat mixed. When cells detoxify unwanted contaminants, there are two key steps involved in the process. In a first step (called Phase 1), potentially damaging molecules are made more reactive so that they can be passed on to Phase 2. In this second, Phase 2 step, the activated molecules get neutralized by being combined with a second neutralizing molecule. Flavonoids can impact both steps in detoxification (Phase 1 and Phase 2). With Phase 2, these influences seems fairly consistent because they tend to promote the combining/neutralizing goal of Phase 2. However, with respect to Phase 1, the role of flavonoids is more complicated since they can switch Phase 1 either on or off. In other words, they can both facilitate and block this first step in detoxification. This complicated relationship between flavonoids and detoxification has resulted in some mixed research findings, although overall, most researchers have concluded that strong flavonoid intake modified detoxification in a helpful way and decreases the risk of problems from unwanted toxins.

Another potential benefit is better regulation of cell cycles. Most cells go through stages of activity where they rest, divide, or go into a self-dismantling and self-recycling process called apoptosis. For the health of all body systems, it is important for these cell cycle stages to stay in balance. Ample intake of food flavonoids appears to promote these cell cycle balances, most likely through regulation of signaling that takes place between cells and their surroundings.

Summary of food sources

Flavonoids are produced by plants, and plant foods are by far our greatest source of these health-supporting phytonutrients. Among all plant food groups, by far it’s been fruits and vegetables that have been best studied and most analyzed for their flavonoid content. There is also flavonoid data on nuts and seeds, grains, beans and legumes, and select other foods and beverages (for example, green and black tea).

It’s important to remember that flavonoids are a very large (more than 6,000 have been so far identified) and very diverse group of phytonutrients. The U.S. Department of Agriculture’s (USDA) Flavonoid Database actually breaks down its flavonoid analyses into five of the basic flavonoid chemical subgroups, and it analyzes the best food choices in each of these subgroups. This approach to understanding the flavonoid content of food, because it emphasizes the need to consume a wide variety of flavonoids that includes all of the different types. In keeping with this approach, the charts below will show you our top WHF in each of the flavonoid subcategories. The five subcategories shown in the charts below are: (1) flavonols (which include quercetin, kaempferol, myricetin, and isorhamnetin); (2) flavan-3-ols (which include catechins, epicatechins, gallocatechins, and theaflavins); (3) flavones (which include apigenin and luteolin); (4) flavonones (which include hesperetin, naringenin, and eriodictyol); and (5) anthocyanidins (which include cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin).

Best sources of flavonoids

flavonols

flavan-3-ols*

flavones

flavonones

anthocyanidins

onions

apples

parsley

oranges

blueberries

apples

bananas

bell peppers

grapefruit

bananas

romaine lettuce

blueberries

celery

lemons

strawberries

tomatoes

peaches

apples

tomatoes

cherries

garbanzo beans

pears

oranges

pears

almonds

strawberries

watermelon

cabbage

turnip greens

chili peppers

cranberries

sweet potatoes

cantaloupe

plums

quinoa

lettuce

raspberries

garbanzo beans

*It’s important to note that in the U.S. the largest single source of flavonoids is black and green tea, and that over half of all flavonoid intake comes from the flavan-3-ol subgroup that is so concentrated in tea; this subgroup includes catechins, epicatechins, gallocatechins, and theaflavins.

As you can see, it takes a variety of foods from a variety of different food groups to give you a good cross-section of flavonoid subcategories. The USDA estimates that in the U.S., daily total flavonoid consumption by the average adult is approximately 250-275 milligrams, with about half of total consumption coming in the form of flavan-3-ols from black and green tea.

The colorful reds, blues, and purples in berries are provided by their anthocyanidins, and that is why you find so many of these fruits listed in the anthocyanidin column.

As a group of phytonutrients, flavonoids emphasize,in a way that is not as well emphasized by perhaps any other nutrient,how valuable fruits and vegetables are to our nourishment and everyday health.

Impact of cooking, storage and processing

You will lose some flavonoids from plant foods during prolonged storage. For example, onions stored at room temperature will lose about one quarter to one third of their original flavonoid content over six months, with most of the loss occurring in the first two weeks.

As water-soluble nutrients, flavonoids can be lost through water contact, and in some cases, up to 80% of specific flavonoids can be lost into cooking water during the boiling of foods. Because many flavonoids provide visible colors in a food, loss of flavonoids during boiling can often be seen in a dulling of the food’s colors. Color changes of this kind indicate overcooking; when boiling or steaming dulls a food’s colors, significant nutrient loss, including flavonoids, has occurred.

Flavonoids are susceptible to damage by heat, and as mentioned earlier, they are also susceptible to damage over prolonged periods of time. Freshness matters: the fresher the produce at time of purchase, the higher its flavonoid content is likely to be. Heat susceptibility is one reason to avoid frying or lengthy cooking even at medium temperatures. (The WHF Healthy Saute method, for example, typically calls for cooking times of 5-8 minutes or less.)

Flavonoids concentrate in the skins and outer portions of fruits and vegetables. These portions are worth consuming, though they should be washed and gently scrubbed with a vegetable brush to reduce contamination risk. Certified organic produce reduces this concern further. Flavonoid-rich foods store best in whole, natural form without pre-cutting, pre-slicing, or pre-peeling before refrigeration.

Risk of dietary deficiency

As mentioned earlier, average consumption of flavonoids in the U.S. is far less than 1 gram per day (at about 250-275 milligrams), with black and green tea serving as the number one source of these phytonutrients. This level of intake is likely inadequate from a health standpoint, though no good standard exists for determining optimal flavonoid amounts. There is no Dietary Reference Intake (DRI) for flavonoids and no Daily Value (DV); in addition, nutrient databases do no provide anywhere close to comprehensive information about the overall flavonoid content of foods. All of these limitations make statements about dietary deficiency somewhat tentative. However, from a common sense standpoint, let’s say that a person consumed six vegetable and four fruit servings in a day, for a total of 10 vegetable-plus-fruit servings. Furthermore, let’s say that all of these servings came from whole, natural foods. In this situation, a person’s total flavonoid intake would be likely to fall somewhere near 1 gram (1,000 milligrams) or more. In this context, average flavonoid intake in the U.S. appears inadequate. In addition, since a disproportional amount of U.S. flavonoids come from a single flavonoid subgroup (flavan-3-ols provided from black and green tea), there is likely to be flavonoid deficiency from the other subgroups given the pattern of flavonoid consumption in the U.S.

Risk of dietary deficiency for flavonoids is basically synonymous with low dietary intake of whole, natural foods, and in particular, low intake of vegetables and fruits. The most reliable way to ensure ample flavonoid intake is to consume whole natural foods, especially fresh, brightly colored vegetables and fruits whose flavonoid pigments provide their characteristic colors.

Other circumstances that might contribute to deficiency

Most documented risks for flavonoid deficiency have already been discussed since they involve poor dietary intake. Overconsumption of processed foods, overcooking of foods, and underconsumption of fresh vegetables and fruits are the primary circumstances related to deficiency. Problems with the chewing of fresh foods can increase a person’s flavonoid deficiency risk, especially if these foods are avoided in a meal plan due to chewing problems. Lack of appetite can also put a person at risk of deficiency, simply due to overall low intake. In studies of the overall U.S. population, inadequate intake of nutrients,including flavonoids,can be associated with poverty and general lack of access to fresh foods.

Relationship with other nutrients

As described earlier, a unique relationship exists between flavonoids and vitamin C. Flavonoids affect the transport of vitamin C around the body, and they also help regulate the function of an enzyme called ascorbate oxidase, which converts vitamin C into a non-vitamin form (monodehydroascorbate). The full significance of these interactions is not yet understood, but these nutrients have a special and unique relationship. This relationship is consistent with the observation that many foods are high in both flavonoids and vitamin C. The top five WHF for vitamin C (papaya, bell peppers, broccoli, Brussels sprouts, strawberries) are all rich in flavonoids as well.

Risk of dietary toxicity

No evidence indicates that dietary flavonoids are directly toxic, even in meal plans that contain an abundance of fresh vegetables and fruits as well as an abundance of nuts, seeds, beans, legumes, and whole grains. When consumption of the foods above is very high, the total fiber content of the diet usually goes up dramatically. (In comparison to average fiber intake in the U.S., which averages about 16 grams per day, fiber intake in countries with high consumption of the foods above often exceeds 100 grams. (The WHF Healthiest Way of Eating Plan averages over 50 grams of daily fiber.) High flavonoid intake from whole natural foods would naturally accompany high fiber intake, and no toxicity risks have been associated with this dietary pattern.

In addition, since flavonoids are water-soluble, they likely follow the pattern of other water-soluble nutrients, which involves lower risk of toxicity than is associated with fat-soluble nutrients, and in many cases, a decision by the National Academy of Sciences (NAS) not to establish a Tolerable Upper Intake Level (UL) for water-soluble vitamins like vitamin B1 or vitamin B2 when obtained from food. A similar decision might end up holding true for flavonoids as well, although it’s important to remember that the NAS has yet to even establish flavonoids as a required human nutrient or to set Dietary Reference Intake (DRI) amounts for flavonoids as a group or for any specific flavonoid.

Disease checklist

Public health recommendations

As described earlier, there are no specific public health recommendations for flavonoid intake. There are currently no Dietary Reference Intakes (DRIs) from the National Academy of Sciences and there is no Daily Value (DV) from the U.S. Food and Drug Administration. However, as described earlier in our Risk of Dietary Toxicity section, the recommendation for optimal flavonoid intake is to focus on a whole, natural, fresh foods diet that provides ample servings of vegetables and fruits. In many of the WHF sample daily meal plans, the total vegetable-plus-fruit servings add up to 5-8 servings or more. When coupled with other flavonoid-rich foods,including nuts, seeds, beans, legumes, and whole grains,flavonoid intake is likely to far surpass the current U.S. average level of approximately 250-275 milligrams, and may in fact get closer to a level of approaching 1 gram (1,000 milligrams).

What can high-flavonoid foods do for you?

What events can indicate a need for more high-flavonoid foods?

Sources of flavonoids include: apples, apricots, blueberries, pears, raspberries, strawberries, black beans, cabbage, onions, parsley, pinto beans, and tomatoes.

For serving size for specific foods see the Nutrient Rating Chart.

Description

What are flavonoids?

Flavonoids, an amazing array of over 6,000 different substances found in virtually all plants, are responsible for many of the plant colors that dazzle us with their brilliant shades of yellow, orange, and red.

Classified as plant pigments, flavonoids were discovered in 1938 when a Hungarian scientist named Albert Szent-Gyorgyi used the term “vitamin P” to describe them.

The chemistry of flavonoids is complicated, and within the non-technical term “flavonoids” can be found many different chemical groups of substances. These groups include flavonols, dihydroflavonols, flavones, isoflavones, flavanones, anthocyanins, and anthocyanidins. Within each of these groups fall hundreds, and sometimes thousands of different flavonoids.

For example, well-known flavonols include quercetin, rutin, and hesperidin, while well-known flavones include apigenin and luteolin. Flavonoids may also be named directly after the unique plant that contains them. Ginkgetin is a flavonoid from the ginkgo tree, and tangeretin is a flavonoid from the tangerine.

How it functions

What is are the functions of flavonoids?

Protection of cell structures

Most flavonoids function in the human body as antioxidants. In this capacity, they help neutralize overly reactive oxygen-containing molecules and prevent these overly reactive molecules from damaging parts of cells. Particularly in oriental medicine, plant flavonoids have been used for centuries in conjunction with their antioxidant, protective properties. Scultellaria root, cornus fruit, licorice, and green tea are examples of flavonoid-containing foods widely used in oriental medicine. While flavonoids may exert their cell structure protection through a variety of mechanisms, one of their potent effects may be through their ability to increase levels of glutathione, a powerful antioxidant, as suggested by various research studies.

Vitamin C support

The relationship between flavonoids and vitamin C was actually discovered by mistake. Dr. Albert Szent-Gyorgyi, the Nobel Prize winning researcher who discovered flavonoids, was attempting to make a preparation of vitamin C for one of his patients with blood vessel problems. The preparation he gave the patient was not 100% pure—it contained other substances along with the vitamin C. It worked amazingly well.

Later, when Dr. Szent-Gyorgyi purchased a pure solution of vitamin C, he found it was not nearly so effective with his patient. He suspected flavonoids as the magic addition to vitamin C in his first impure preparation. Present-day research has clearly documented the synergistic (mutually beneficial) relationship between flavonoids and vitamin C. Each substance improves the antioxidant activity of the other, and many of the vitamin-related functions of vitamin C also appear to require the presence of flavonoids.

Inflammation control

Inflammation—the body’s natural response to danger or damage—must always be carefully regulated to prevent overactivation of the immune system and unwanted immune response. Many types of cells involved with the immune system—including T cells, B cells, NK cells, mast cells, and neutrophils—have been shown to alter their behavior in the presence of flavonoids. Prevention of excessive inflammation appear to be a key role played by many different chemical categories of flavonoids.

Antibiotic activity

In some cases, flavonoids can act directly as antibiotics by disrupting the function of microorganisms like viruses or bacteria. The antiviral function of flavonoids has been demonstrated with the HIV virus, and also with HSV-1, a herpes simplex virus.

Deficiency symptoms

What are deficiency symptoms for flavonoids?

Excessive bruisability, nose bleeds, swelling after injury, and hemorrhoids can be indicators of flavonoid deficiency. Generally weakened immune function, as evidenced by frequent colds or infections, can also be a sign of inadequate dietary intake of flavonoids.

Toxicity symptoms

What are toxicity symptoms for flavonoids?

Even in very high amounts (for example, 140 grams per day), flavonoids do not appear to cause unwanted side effects. Even when raised to the level of 10% of total caloric intake, flavonoid supplementation has been shown non-toxic. Studies during pregnancy have also failed to show problems with high-level intake of flavonoids.

Factors that affect function

What factors might contribute to a deficiency of flavonoids?

Poor intake of fruits and vegetables—or routine intake of high-processed fruits and vegetables—are common contributing factors to flavonoid deficiency. It is difficult to overemphasize the impact of processing and a non-whole foods diet on flavonoid intake. If the pulpy, fibrous parts of fruits are eliminated from the juice, and the vibrant natural colors of canned vegetables are lost during repeated heating, risk of flavonoid deficiency is greatly increased.

Nutrient interactions

How do other nutrients interact with flavonoids?

Present-day research has clearly documented the synergistic (mutually beneficial) relationship between flavonoids and vitamin C. Each substance improves the antioxidant activity of the other, and many of the vitamin-related functions of vitamin C also appear to require the presence of flavonoids.

Health conditions

What health conditions require special emphasis on flavonoids?

Flavonoids may play a role in the prevention and/or treatment of the following health conditions:

Food sources

What foods provide flavonoids?

Virtually all fruits, vegetables, herbs and spices contain flavonoids. They are also found in other types of food, including dry beans (where they give red beans,black beans, and speckled beans their color) and grains (where the color provided by flavonoids is usually in the yellow family). Products made from the foods above (for example, wines made from grapes) also typically contain a wide variety of flavonoids.

While the flavonoid family is too complex to report all of its food connections, some highlights are especially important. In the fruit family, it is berries that come out highest in the chemical category of flavonoids called anthocyanins. Black raspberries, for example, may contain up to 100 milligrams of anthocyanins per ounce.

Green tea has flavonoid components called catechins that may reach 1,000 milligrams (or 1 gram) per cup. In general, the more colorful components of the food—like the skins of fruits—contain the highest concentration of flavonoids. However, flavonoids can be both white and green in color, and for this reason may show up in less noticeable ways in food. One example involves the white pulpy inside of oranges. In addition being found in the watery orange-colored sections of this fruit (which contain virtually all of the orange’s vitamin C content), the orange’s flavonoids can also be found in the white pulpy portion inside the skin and surrounding the sections.

Nutrient rating chart

Food Source Analysis not Available for this Nutrient

What events can indicate a need for more high-flavonoid foods?

Sources of flavonoids include: apples, apricots, blueberries, pears, raspberries, strawberries, black beans, cabbage, onions, parsley, pinto beans, and tomatoes.

For serving size for specific foods, see Nutrient Rating Chart below at the bottom of this page.

Related Articles

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