For decades, polyphenols were primarily considered plant-based antioxidants that neutralize harmful free radicals. But this view is long outdated. Current research shows that polyphenols are, in fact, highly effective signaling molecules that specifically intervene in cellular communication networks. They activate detoxification enzymes, regulate inflammatory processes, and even control the quality assurance of our mitochondria. This paradigm shift has far-reaching consequences for our understanding of healthy nutrition.
The paradigm shift: From radical scavengers to signal transmitters
The traditional view was simple and plausible: polyphenols – secondary plant compounds found in fruits, vegetables, tea, and red wine – work by directly neutralizing free radicals. This chemical antioxidant theory dominated nutritional research for decades.
However, this view is too simplistic. A comprehensive review article in the International Journal of Molecular Sciences (January 2026) clarifies that the health effects of polyphenols cannot be explained solely by their direct antioxidant capacity. Their concentrations in the body after consuming plant-based foods are far too low for that.
The researchers emphasize: "The modulation of cellular signaling pathways often goes beyond immediate antioxidant effects and may influence long-term cellular conditions such as inflammatory responses and metabolic adaptations." In other words, polyphenols primarily act as signaling molecules that tell the cell: "Activate your protective mechanisms!"
The most important signaling pathways: Where polyphenols intervene
Current research has identified several key signaling pathways that are modulated by polyphenols.
The Nrf2 signaling pathway – the activation of the body's own defense system
Perhaps the most important mechanism is the activation of the Nrf2 signaling pathway. Nrf2 (nuclear factor erythroid 2-related factor 2) is considered the "master regulator" of antioxidant defense. Under normal conditions, Nrf2 is retained in the cell cytoplasm and broken down. In cases of oxidative stress or due to certain polyphenols, this mechanism is disrupted; Nrf2 migrates into the cell nucleus and activates the production of the body's own protective enzymes there. .
A study using barley sprout extract impressively demonstrated how this works in practice: The addition of the phenolic extract activated the Nrf2/ARE signaling pathway and led to a significant increase in the activity of important antioxidant enzymes. :
-
Glutathione peroxidase : +27.2%
-
Superoxide dismutase : +24.6%
-
Catalase : +61.7%
-
Heme oxygenase-1 : +50.4%
The crucial point: Here, the polyphenols do not act as radical scavengers, but as signaling molecules that stimulate the cell to build its own protective shield.
Anti-inflammatory action via NF-κB
Another key target is the transcription factor NF-κB, which is considered a master switch for inflammatory processes. A review article in Frontiers in Pharmacology describes how polyphenols inhibit pro-inflammatory signaling pathways such as NF-κB, COX-2, and iNOS, and reduce the concentration of pro-inflammatory messengers such as TNF-α, IL-1β, and IL-6. .
In parallel, polyphenols modulate other signal transduction pathways, including MAPK, PI3K/Akt, and STAT signaling pathways, which are relevant for neuronal survival, synaptic plasticity, autophagy, and proteostasis. .
Regulation of microglia and nitric oxide production
A specific review article in Medical Gas Research (June 2026) focuses on the effect of polyphenols on microglia – the brain's immune cells. These cells can produce large amounts of nitric oxide (NO) when overactivated, which damages nerve cells.
The researchers show that plant phenolic compounds modulate the key signaling pathways NF-κB, MAPK, Nrf2 and PI3K/Akt, thereby suppressing the expression of inducible NO synthase (iNOS). . In doing so, they reduce oxidative and nitrosative stress and restore immune homeostasis.
The new perspective: An integrated model
Modern research integrates the various levels of action into a comprehensive picture. The review article in the International Journal of Molecular Sciences emphasizes the "integration of direct antioxidant chemistry, redox signaling, and mitochondrial quality control within a unified mechanistic framework." .
This means that polyphenols work on several levels simultaneously:
-
Direct radical scavenging (at high concentrations)
-
Activation of protective signaling pathways (Nrf2, inhibition of NF-κB)
-
Influence on mitochondrial function and autophagy
The importance of metabolites
A crucial step forward in our understanding is the realization that it is not necessarily the polyphenols themselves, found in the plant, that are effective, but rather their metabolites in the body. A review article in the Journal of Nutritional Biochemistry (January 2026) examines precisely these "circulating (poly)phenol metabolites" such as valerolactones, benzoic acid derivatives, urolithins, and hydroxycinnamic acids. .
These metabolites can modulate the ubiquitin-proteasome system (UPS) – a central cellular mechanism for protein degradation that plays a role in chronic diseases such as neurodegenerative, cardiovascular, and oncological disorders. However, the researchers emphasize: "While bioavailability studies have described the absorption and metabolism of dietary polyphenols, less is known about which specific metabolites reach target tissues in biologically active concentrations." .
Practical consequences: What does this mean for nutrition?
The finding that polyphenols act as signaling molecules has practical consequences for our diet.
Diversity is crucial
Since different polyphenols act on different signaling pathways, a diverse intake is beneficial. The review article in Frontiers in Pharmacology emphasizes that polyphenols "broadly intervene in inflammatory, oxidative, and cellular stress mechanisms." .
The dose makes the signaling substance
For signaling effects, lower concentrations are often sufficient than for direct radical scavenging. This explains why even moderate amounts of fruit and vegetables can have health-promoting effects.
The role of the microbiome
Gut bacteria play a crucial role in converting polyphenols into active metabolites. Research refers to "microbiota-driven biotransformation" as a key factor for their efficacy. .
Limits of research
Despite the impressive progress, the researchers point out several limitations. :
-
Current knowledge is largely based on cell culture models and animal experiments, often using supraphysiological doses.
-
The applicability to humans is still insufficiently researched.
-
The large interindividual variability (due to different microbiomes) makes standardized recommendations difficult.
-
Clinical studies with physiologically relevant concentrations and chronic exposure patterns are largely lacking.
Conclusion
Research conducted in 2025 and 2026 has fundamentally changed our understanding of polyphenols. They are not primarily free radical scavengers, but highly effective signaling molecules that communicate with central regulatory systems in our cells. They activate the body's own protective switches (Nrf2), suppress inflammation (NF-κB), and even influence the quality control of our mitochondria.
In practical terms, this means that a polyphenol-rich diet with plenty of fruits, vegetables, tea, and high-quality plant oils is more than just an "antioxidant supply"—it's a dialogue with our cells that stimulates them to stay healthy. However, research is only just beginning to fully understand the complex signaling networks and the role of individual metabolic and microbiome differences.
Official sources & studies:
-
Jalouli M et al.: Targeting natural antioxidant polyphenols to protect neuroinflammation and neurodegenerative diseases (Frontiers in Pharmacology, 2025) - quoted from naturmed-praxis.de
-
Ferreira S et al.: Modulation of the ubiquitin-proteasome system by circulating (poly)phenol-derived metabolites (Journal of Nutritional Biochemistry, January 2026) - PubMed
-
Dietary Polyphenols (Flavonoids) Derived from Plants for Use in Therapeutic Health (International Journal of Molecular Sciences, January 2026)
-
Sahakyan N: Plant-derived phenolics as regulators of nitric oxide production in microglia (Medical Gas Research, June 2026) - PubMed/LWW
-
Wang M et al.: Investigation of the composition and antioxidant properties of phenolic compounds from barley seedlings (Journal of Future Foods, January 2026) – ScienceDirect
