Talk:Flavonoid

Nutritional Value

Is there anything known about the nutritional value of this allegedly dietary chemical? The article seems to focus a lot on what this class of chemicals doesn't do (Which at times seems rather absurd. Do we really need 4 references to show flavonoids are not a prescription drug? Why is this even relevant?). I assume this is perhaps to combat misinformation though the article doesn't actually mention any controversy, or what misinformation it's attempting to combat. It also doesn't really mention what is known about this chemical's biological activity (if anything). 184.180.243.223 (talk) 05:55, 29 August 2025 (UTC)

They are non-nutrient antioxidants, they have no nutritional value. Veg Historian (talk) 13:29, 29 August 2025 (UTC)

As flavonoids are a chemical class within the parent category of polyphenols, this discussion from the polyphenol article applies.

Although showing "antioxidant" activity in test tube experiments, there is no evidence that flavonoids have dietary antioxidant activity or nutritional value, i.e., they have no proven biological effects in vivo. Quoting from the polyphenol article, "Polyphenols were once considered as antioxidants, but this concept is obsolete. Most polyphenols are metabolized by catechol-O-methyltransferase, and therefore do not have the chemical structure allowing antioxidant activity in vivo; they may exert biological activity as signaling molecules."

Definitive publications on the fate of flavonoids (and polyphenols, generally) are rare because these food compounds are cleaved during digestion into smaller metabolites which cannot be traced in the body specifically to target organs. The metabolites are excreted rapidly in the urine, indicating they are unlikely to have binding or functional properties typical of a hormone or drug with specific cellular targets.

In Europe by EFSA and the United States by the FDA, flavonoids have no designation as dietary antioxidants or nutrients. The EFSA document itemizes cases where no cause-and-effect relationship can be shown between flavonoids and antioxidant activity (hundreds of flavonoid examples with antioxidant claims are given in Part 2.)

These facts seem to be difficult for the general public to absorb, as there are countless layperson reports, news, blogs, woo articles, etc. proclaiming colorful "flavonoid" foods like blueberries, cherries, apples, citrus fruits, etc. are "rich in antioxidants", yet no quality WP:BMI review sources support this. Individual levels of vitamins A, C, and/or E as they apply for such foods are the only dietary antioxidants.

Regarding the issues raised by IP 184.180.243.223: perhaps these can be focused to

1) how do we clearly define the non-nutrient status of flavonoids?

2) how do we better define the non-antioxidant status of flavonoids, and clearly show health claims are not valid or approved?

3) rather than addressing a "controversy", how do we clarify the absence of scientific proof for biological activity from dietary intake?

As the IP inferred, excluding discussion of these topics gives the impression of deterring misinformation, but the challenge will be providing sources to nail it down. Some of these points are partially addressed by the paragraphs under Research in the flavonoid and polyphenol articles. Zefr (talk) 16:37, 29 August 2025 (UTC)

From what I see they have no direct antioxidant effect. In regard to the current status of flavonoids and these unreliable health claims would this paper help clarify the issues? . This was a review from the International Life Sciences Institute Europe working group. Maybe add that source if you think it is useful here because it goes into a lot of detail including some of what you have described above.

The only other free source that covers this in brief is the Linus Pauling Institute which has a section "Direct antioxidant activity" which concludes "the relative contribution of dietary flavonoids to plasma and tissue antioxidant function in vivo is likely to be very small or negligible". There are several listed reasons for this, the main being flavonoid concentrations in humans even at high doses are "100 to 1,000 times lower" than other antioxidants like vitamin C. Perhaps adding a line about this might be useful to the reader or resolve what the IP was after. Veg Historian (talk) 19:53, 29 August 2025 (UTC)

Honestly, just adding a brief summary of those points at the top of the Research section, or even @Veg Historian's initial response to that paragraph would go a long way. Perhaps the Research section could be rewritten from the initial position that these chemicals have no verified nutritional value, and the other research offering supporting evidence of this position, with breakdowns noting specific health benefits that have been investigated (like cancer, inflammation, etc) without meaningful results. I don't think a huge change is needed here. And thank you all for your work. 184.180.243.223 (talk) 23:45, 29 August 2025 (UTC)

With Special:Diff/1308856717, I made a general edit and addressed the non-nutrient status and absence of causality evidence for the presumed physiological antioxidant effects in humans. Open for further discussion and editing. Zefr (talk) 22:17, 31 August 2025 (UTC)

The statements “Flavonoids are non-nutrient antioxidants” and "Flavonoids have no antioxidant activity in vivo" cannot both be true. It is inaccurate to call something a non-nutrient antioxidant while asserting it has no antioxidant function. It’s like calling water a “non-nutrient diuretic” but then saying “it doesn’t make you urinate.”

Flavonoids are non-nutrient polyphenols. They show antioxidant activity in vitro, but this does not translate in vivo, because plasma concentrations are far too low for direct radical scavenging. Their real importance lies in cell-signaling and gene-regulatory actions that up-regulate endogenous antioxidant systems (Nrf2-mediated glutathione synthesis, SOD, catalase). Thus, flavonoids are antioxidant-modulating, not antioxidants per se.

A more scientifically accurate restatement might take the following form: “Flavonoids are non-nutrient polyphenolic compounds. They do not act as direct antioxidants in the body but can influence antioxidant defenses and other physiological processes through cell-signaling pathways.” 0gravitytampabay (talk) 16:44, 9 November 2025 (UTC)

The statement that flavonoids "influence antioxidant defenses and other physiological processes through cell-signaling pathways" is conjecture only from in vitro studies, so is unsupportable for adding to the article. There are no WP:MEDRS reviews, no international clinical guidelines, and no substantial scientific consensus that flavonoids have such functions in vivo.

This applies to your points below. The EFSA opinion review is cited in the article, but it defines the cocoa effect only from an exceptional (unrealistic) amount of cocoa flavonoid intake (200 mg of specific flavonoids per day), and the physiological effect is vague for whether it has systemic significance. The LPI review makes no certain conclusions about flavonoid intake having any significant clinical effect. Zefr (talk) 18:15, 9 November 2025 (UTC)

Flavonoids (introductory paragraphs)

The sentence in the second paragraph: “Flavonoids … have no established effects on human health or prevention of disease” is not supported by current secondary literature or regulatory findings. It is therefore inaccurate under WP:V and WP:ACCURACY.

1. Regulatory evidence – The European Food Safety Authority (EFSA, 2012, EFSA Journal 10(7):2809) concluded there is a cause-and-effect relationship between cocoa flavanols and maintenance of normal endothelium-dependent vasodilation at intakes of 200 mg/day. That is an established human physiological effect.

2. Human clinical evidence – Multiple meta-analyses and systematic reviews document reproducible physiological outcomes: – Hooper L et al., Am J Clin Nutr 2012 95:740 – meta-analysis of 42 RCTs → ↑ flow-mediated dilation and ↓ systolic BP (~2–4 mm Hg). – Khan N & Mukhtar H, J Nutr 2014 144:1677 – tea catechins → improved vascular function and lipid profile. – Whyte A R et al., Nutrients 2021 13:4143 – anthocyanin-rich berries → better cerebral perfusion and cognitive performance. – Xu Y et al., Phytother Res 2020 34:122 – quercetin → modest improvement in HOMA-IR and fasting glucose.

3. Mechanistic clarification (2025) - A new peer-reviewed study from Shibaura Institute of Technology (Fujii Y et al., “Astringent flavanol fires the locus-noradrenergic system, regulating neurobehavior and autonomic nerves,” Current Research in Food Science 2025, DOI 10.1016/j.crfs.2025.101195) shows that orally administered astringent flavanols activate corticotropin-releasing-hormone neurons and the locus coeruleus–noradrenergic network, enhancing arousal and memory in mice. The authors propose a sensory-neural mechanism—taste receptor stimulation transmitting signals to the CNS—explaining how flavanols can influence brain function despite low plasma bioavailability.

4. Summary of consensus evidence - Flavonoids are non-essential nutrients and lack significant direct antioxidant activity in vivo. Nevertheless, multiple subclasses (flavanols, catechins, anthocyanins, quercetin) show measurable, reproducible physiological effects in humans and clear mechanistic plausibility.

Suggested neutral revision:

“Flavonoids are not essential nutrients and do not act as direct antioxidants in the body; however, they can modulate antioxidant defenses and other physiological functions through cell-signaling pathways. Several subclasses have demonstrated measurable effects in humans—including vascular, metabolic, and neurocognitive responses—though the relevance of these findings to long-term disease prevention remains under investigation.”

This formulation aligns with EFSA (2012), the Linus Pauling Institute (2023 update), and current peer-reviewed literature while avoiding unsourced medical claims.

Key citations:

EFSA Panel on Dietetic Products, Nutrition and Allergies (2012). EFSA Journal 10(7):2809 “Scientific Opinion on the substantiation of health claims related to cocoa flavanols and maintenance of normal endothelium-dependent vasodilation.”

Hooper L et al. (2012). Am J Clin Nutr 95:740–751.

Whyte A R et al. (2021). Nutrients 13:4143.

Xu Y et al. (2020). Phytother Res 34:122–137.

Fujii Y et al. (2025). Current Research in Food Science 10.1016/j.crfs.2025.101195.

Linus Pauling Institute. “Flavonoids.” Micronutrient Information Center (2023 revision).

Fujii Y et al., “Astringent flavanol fires the locus-noradrenergic system, regulating neurobehavior and autonomic nerves,” Current Research in Food Science 2025, DOI 10.1016/j.crfs.2025.101195 0gravitytampabay (talk) 17:06, 9 November 2025 (UTC)

See comment in above section. The statement “Flavonoids … have no established effects on human health or prevention of disease” remains accurate. "Established effects" would mean there are WP:MEDASSESS sources (top of left pyramid), such as systematic reviews and/or international clinical guidelines proclaiming "consume more flavonoid-rich foods to prevent x disease!", statements which of course do not exist.

Further, if there were established effects of flavonoids on human health, federal organizations like the FDA would include flavonoids among the list of essential nutrients, each having a rigorously-defined Daily Value, which does not exist for flavonoids.

As discussed in the article, the metabolism and fate of flavonoids and their metabolites cannot be measured with precision in vivo, leaving the compounds with unknown and undefinable functions, if any, as they are rapidly excreted (indicating non-useful purposes).

Other than the LPI review and EFSA opinion, the sources you offer do not qualify as WP:MEDRS reviews of any conclusive evidence. Zefr (talk) 18:32, 9 November 2025 (UTC)

Outdated information in research and meteabolism

The research section is a bit outdated. The Linus Pauling Review has last been reviewed in 2016 and misses a number of reviews that have been published since, as well as e.g. new risk assessments for soy or tea catechins.

There are a lot of health claims for various flavonoids, so it might be useful to address them here and make it clear what the evidence says. The lack of essentiality does not say anything about health benefits - fibre is not essential yet has clear health benefits and a DRI/DRV - and the lack of DRV/DRI is also not evidence for a lack of health benefits, as the DRV/DRI process is mainly for essential nutrients and the introduction of other compounds is still under discussion.

The metabolism section could also be improved - there is a huge difference between different compounds, and an absorption of less than 5% is not correct (at least for some compounds, there is a considerably higher uptake). As bioavailability is interpreted slightly differently in nutrition research, it might be useful to be quite precise.

I'd be happy to draft something here if there is interest. Ggck2 (talk) 15:19, 27 August 2026 (UTC)

They have low oral bioavailability but the article does not mention technological approaches that have been used to enhance absorption. I have no idea how mainstream or widely used any of these improvement strategies are but this review covers the topic Carrot juice (talk) 20:00, 27 August 2026 (UTC)

There is an added problem that in nutrition, bioavailability is often used different than in pharmacology - so metabolites in various forms are included - so glucuronidation or sulphation does not affect bioavailability in that interpretation. It makes it somewhat confusing, but is nevertheless common practice. Ggck2 (talk) 21:27, 27 August 2026 (UTC)

The proposed draft on flavonoid metabolism seems beyond WP:NOTTEXTBOOK #6,7, and is WP:WFTWA. Zefr (talk) 22:01, 1 September 2026 (UTC)

Why would you say that updating information and making them accurate is WP:NOTTEXTBOOK? The metabolism section is simply outdated and wrong.

As per advice given, there is no need for a COI-template when discussing the article and not making edit requests. Ggck2 (talk) 05:49, 2 September 2026 (UTC)

On the subject of outdated things, I've restored the further reading section (but not any of the database removals). I don't think any of the books that were included in the section encroach on contentious medical things. I have no objection to removal of books that are not relevant, but I restored the section because Harborne's flavonoids is still one of the key all-time greats reviewing the diversity of flavonoids and their distribution across the plant kingdom. It's still factually relevant and it's probably the most widely-cited review of flavonoids ever. Elemimele (talk) 12:00, 14 September 2026 (UTC)

update?

I absolutely don't want to let this article get used to trumpet dubious health claims associated with flavonoids - nearly every paper that's ever been written seems to claim something extravagent - but the tone of the article does seem somewhat at odds with a few more up-to-date reviews such as these: . I am not expert at health matters so I'm just noting the references in case they're relevant to anyone else. My interest is only in flavonoid chemistry in plants... (hence my restoration of Harborne, above) Elemimele (talk) 12:05, 14 September 2026 (UTC)

Harborne is still one of the most relevant sources - and much written there doesn't change.

I wonder whether there is too much emphasis on health aspects and not enough on others. Flavonoids are such a diverse group of compounds that most health effects observed in epidemiological studies are most likely simply the result of a diet rich in fruits and vegetables; it's very different to separate the two. The fact that they are not recognised by any regulatory agency is therefore not really surprising.

What would be interesting would be to update data on ADME/PK. "Poorly absorbed" is not really correct, about 10% of catechins are absorbed, and nutritionists use a different definition of bioavailable (which is unfortunately often a bit confusing). "Rapid excretion" is therefore a bit too generic - some metabolites, especially from gut metabolism, can have half-lives of many hours. Considering the large number of flavonoids, there will be a huge amount of data which will probably be beyond the scope of this article - but it would be good to correct at least the statements that can't be generalised. Ggck2 (talk) 21:54, 14 September 2026 (UTC)

(I probably shouldn't really comment on Harborne, as he worked almost next door to our Department ...).

Ggck2 (talk) 08:10, 15 September 2026 (UTC)

Nutrient status and metabolism

Nutrients in human nutrition are generally considered to be compounds that are essential for live (dietary fibre is a bit of an exception as it is not essential) - not compounds that have an physiological effect (these are more commonly referred to as bioactive compound). The statement on nutrient status should therefore simply state:

1. Flavonoids are not considered as nutrients for humans as they are not essential for survival.

The data on metabolism is not correct - flavonoids are such a complex and diverse group of compounds that a single statement will never describe everything. In addition to this, flavonoid research often uses a slightly different definition of bioavailability, which includes metabolites and therefore can be confusing (e.g. depending on the interpretation, glycosides have a bioavailability of 0 as they are always deglycosylated - but some publications refer to the uptake of the aglycone). For example for the flavanol epicatechin, more than 80% of the compound are taken up by the human body in one form or another, and well over 10% are taken up as conjugated epicatechins (https://www.nature.com/articles/srep29034). Likewise, not all are rapidly excreted with plasma half-lives well above 6h for some compounds.

I think discussing this would go beyond the scope of this article, and suggest the following version revision:

1. The absorption and metabolism for flavonoids by the human body varies considerably between different compounds.[1][2][20][21][22] Flavonoids have negligible antioxidant activity in the body, and the increase in antioxidant capacity of blood seen after consumption of flavonoid-rich foods is not caused directly by flavonoids, but by production of uric acid resulting from flavonoid depolymerization and excretion.[1][2][3] Microbial metabolism is a major contributor to the overall metabolism of dietary flavonoids.[1][2][23]

Ggck2 (talk) 08:13, 20 September 2026 (UTC)

Flavonoids as prescription drugs

{Edit COI|summary="Some flavonoids have been used as prescription drugs."}

The text

Due to the absence of proof for flavonoid health effects in clinical research, neither the United States FDA nor the European Food Safety Authority has approved any flavonoids as prescription drugs.[1][20][24][25]

is not entirely correct, as Catechin actually has been used as a drug more than 40 years ago (see Catechin#Adverse_events). It would also not be the European Food Safety Authority (EFSA) that approves drugs in Europe but the European Medicines Agency (EMA). I suggest the following change:

Flavonoid are currently not authorised as prescription drugs in Europe or the US.[1][20][24][25]

Ggck2 (talk) 08:29, 20 September 2026 (UTC)