Polyphenol — Glossary

Polyphenols are a structurally diverse class of plant-derived secondary metabolites characterised by multiple phenolic hydroxyl groups, found widely across fruits, vegetables, legumes, and botanical preparations.

The term "polyphenol" covers several thousand individual compounds, conventionally organised into subclasses: flavonoids (including flavonols, flavanones, anthocyanins, and isoflavones), phenolic acids (hydroxybenzoic and hydroxycinnamic acid derivatives), stilbenes, and lignans. The precise boundaries of the classification vary between sources; some frameworks include tannins and curcuminoids, whilst others treat these as distinct groupings.

Polyphenols are synthesised in plants primarily via the shikimate and phenylpropanoid pathways. They function ecologically as pigments, UV screens, feeding deterrents, and signalling molecules in plant–microbe interactions. Their concentration in any given plant material is highly variable, depending on cultivar, growing conditions, harvest time, and post-harvest handling.

Considerable laboratory and epidemiological research has examined polyphenols in recent decades. A persistent limitation across this body of work is low oral bioavailability: most polyphenols are extensively metabolised by intestinal and hepatic enzymes, and by the gut microbiota, before reaching systemic circulation. The biological activity of resultant metabolites is an active area of phytochemical research and is not yet fully characterised. No regulatory claim of therapeutic effect should be inferred from mechanistic or in vitro findings alone.

In Australia, polyphenol-containing botanical ingredients in listed medicines (AUST L) must comply with the Therapeutic Goods Act 1989 and the evidence requirements set out by the Therapeutic Goods Administration (TGA). Permitted indications are restricted to those on the TGA's permitted indications list; no serious-disease representations are permissible without full registration (AUST R) status.

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