Fisetin: What the Plant Compound Is, Occurrence & Use

Fisetin is a secondary plant compound from the group of flavonoids, more precisely the flavonols. The yellow pigment occurs naturally in various types of fruit and vegetables, above all in strawberries. In recent years, fisetin has become better known as a component of food supplements and is frequently mentioned in connection with other flavonoids such as quercetin. Anyone dealing with fisetin should first understand what substance it is chemically, in which foods it occurs, in which forms it is offered and what to look out for when selecting and using it. This guide classifies the facts objectively, without health-related promises of effect, because in the EU no health-related claims are authorised for fisetin.

What is fisetin?

Fisetin belongs to the polyphenols and there to the subgroup of flavonols, to which quercetin and kaempferol also belong. Chemically it is a yellow pigment that is formed in plants as a secondary plant compound. Secondary plant compounds are substances that plants do not need for pure growth, but which serve, among other things, as pigments, for defence against predators or for protection from environmental influences.

For humans, fisetin is not an essential nutrient, meaning the body does not depend on a certain intake and also develops no deficiency symptoms when fisetin is lacking. It is one of the bioactive accompanying substances of a plant-rich diet. In research, fisetin is investigated like many flavonoids, among other things in the laboratory and in animal models. Transferable, authorised health-related statements for humans, however, do not exist in the EU for this substance.

Occurrence in foods

Fisetin is contained in several plant foods, although mostly in small amounts. The highest contents are usually described in strawberries. Further sources include apples, grapes, onions and some types of vegetables. The contents vary considerably depending on variety, degree of ripeness, cultivation conditions and storage.

• Strawberries: considered one of the richest natural sources of fisetin.
• Apples and grapes: contain fisetin in smaller amounts, in part especially in the skin.
• Onions: supply, in addition to quercetin, some fisetin as well.

Through a normal mixed diet only comparatively small amounts of fisetin are taken in. Anyone who wants to increase the proportion of flavonoids in the diet basically benefits from a colourful, fruit- and vegetable-rich diet, as is also recommended by professional societies such as the German Nutrition Society. The consumption of whole, little-processed fruit thereby supplies, in addition to fisetin, numerous further accompanying substances.

Forms as a supplement

As a food supplement, fisetin is predominantly offered as an extract, often obtained from the smoke tree or other fisetin-rich plants. Common dosage forms are capsules with a standardised fisetin content as well as occasionally powder. The concentration in such products is significantly above what can be achieved through food.

Since fisetin, like many flavonoids, is fat-soluble and poorly water-soluble, some products combine it with oils or special formulations in order to support absorption. Such additives are intended to increase bioavailability, that is the proportion that actually reaches the body. Fisetin is also often offered together with other polyphenols such as quercetin in combination preparations. When selecting, pay attention to the actually stated pure fisetin content per portion, not just the total amount of the extract.

Intake and dosage

Binding official dosage recommendations for fisetin do not exist, since it is classified as a bioactive plant compound and not as an essential nutrient. Manufacturers state different amounts, which mostly move in the range of a few hundred milligrams per day. Since fisetin is fat-soluble, intake is often recommended with a meal containing some fat, because this can support absorption.

Some users do not use fisetin daily on a permanent basis, but in certain rhythms with breaks, as are in part discussed in research. These approaches, however, are not to be understood as a generally valid recommendation. For everyday use the following applies: orient yourself to the dosage information of the respective product and do not exceed the recommended daily amount without professional advice. More is not automatically better with secondary plant compounds, and very high amounts are not sufficiently studied.

What to look for when buying?

When buying, the stated fisetin content per capsule or portion is the most important piece of information. Some products advertise with high extract amounts without stating the pure fisetin proportion, which makes comparison difficult. Reputable suppliers state the origin of the extract, the plant part used and the standardised content.

Pay attention also to a short ingredient list without unnecessary additives and to testing for residues and heavy metals, since plant extracts can be contaminated depending on origin. Combination preparations with further flavonoids can be sensible, but make comparing the individual amounts more difficult. A transparent, ideally independent certificate of analysis is a good sign of quality. Light-protected packaging also helps to preserve the sensitive pigment.

It is also sensible to compare the costs per daily dose instead of the pure pack price, because products differ greatly in capsule count and fisetin content. Anyone who pays attention to plant-based capsule shells or wants to avoid certain additives will find the necessary information on the ingredient list. With combination preparations containing quercetin or other flavonoids, a close look is worthwhile at what ratio the individual substances are contained in, since some products name fisetin prominently but supply only small amounts of it.

Safety and tolerance

Fisetin occurs in usual amounts in many foods and is considered harmless in these amounts. For highly concentrated extracts there is less long-term data, which is why the manufacturer information should not be exceeded. Side effects are rarely described with usual use, but individual intolerances such as gastrointestinal irritation can never be completely ruled out.

Like other polyphenols, fisetin can theoretically interact with medications, for example via breakdown in the liver. If you regularly take medicines, are pregnant, breastfeed or have health complaints, speak with your doctor before taking it. Food supplements do not replace a balanced diet and no medical treatment.

Fisetin in the context of flavonoids

In order to classify fisetin correctly, it helps to take a look at the large group of flavonoids to which it belongs. Flavonoids are an extensive class of secondary plant compounds that occur in almost all plant foods and are divided into several subgroups, including flavonols, flavones, flavanols and anthocyanins. Fisetin, like quercetin, is one of the flavonols. These compounds are co-responsible for many of the yellow, orange and red colour tones in fruit and vegetables.

For nutrition, less the individual substance is decisive than the interplay of many flavonoids and further accompanying substances that one takes in through a plant-rich diet. Professional societies therefore emphasise the value of a varied diet with plenty of fruit, vegetables, herbs and wholegrain products, instead of highlighting individual substances in isolation. An isolated extract does supply a high amount of a single flavonol, but cannot reproduce the diversity of a natural food matrix. This classification is helpful in order to assess the role of fisetin realistically.

Honestly classified

Fisetin is an interesting, much-studied plant compound, but much regarding its significance for humans is still being researched. A large part of the available data comes from laboratory and animal experiments, which cannot readily be transferred to humans. Specific health-related statements are not authorised in the EU, and high concentrations from extracts are not to be equated with the natural occurrence in foods. Anyone who orients themselves to a varied, plant-rich diet takes in fisetin regularly in small amounts anyway and at the same time supplies themselves with many further plant compounds. An extract can sensibly supplement such a diet, but not replace it, because the diversity of nutrients and fibre from whole foods cannot be reproduced by a single substance.

Frequently Asked Questions (FAQ)

What is fisetin?

Fisetin is a secondary plant compound from the group of flavonols, to which quercetin also belongs. It is a yellow pigment that occurs in plants and is not an essential nutrient for humans.

In which foods is fisetin found?

The highest contents are mostly described in strawberries. Further sources are apples, grapes, onions and some types of vegetables, but in each case in rather small amounts.

How is fisetin taken?

As a supplement it is mostly taken as a capsule, often with a fat-containing meal, since fisetin is fat-soluble. Binding official dosages do not exist; follow the information of the manufacturer.

What should I look for when buying?

Important is the stated pure fisetin content per portion, not just the extract amount. Pay attention also to origin, standardised content, few additives and testing for residues.

Is fisetin safe?

In the amounts from foods, fisetin is considered harmless. For highly concentrated extracts there is less long-term data. With medication intake, pregnancy, breastfeeding or illnesses you should obtain medical advice beforehand.