Flavanols Break the Rules of Nutrition: Scientists Uncover the Surprising Way They Boost the Brain

Health & Nutrition

The health benefits of dietary flavanols appear to come from their ability to trigger responses in the brain and the body’s stress systems.

That slightly dry, tightening feeling some foods leave in the mouth is known as astringency, and it comes from naturally occurring plant compounds called polyphenols.

Among them are flavanols, which have attracted attention for their links to lower cardiovascular risk and potential benefits for the brain. These compounds are plentiful in familiar foods like cocoa, red wine, and berries, and studies have associated them with sharper memory, stronger cognitive performance, and protection against damage to nerve cells.

Yet there is a long-standing puzzle: flavanols are poorly absorbed by the body (the fraction that actually enters the bloodstream after ingestion). If only small amounts reach circulation, it remains unclear how they exert measurable effects on the brain and nervous system.

Sensory signaling may explain flavanol effects

Seeking answers, a research group led by Dr. Yasuyuki Fujii and Professor Naomi Osakabe at Shibaura Institute of Technology in Japan explored an alternative explanation. Rather than focusing on absorption alone, they examined whether flavanols might act through sensory pathways, particularly taste.

Their study, published in the journal Current Research in Food Science, tested the idea that the characteristic astringent taste of flavanols could serve as a direct signal to the brain, activating neural responses even before these compounds are fully processed by the body.

“Flavanols exhibit an astringent taste. We hypothesized that this taste serves as a stimulus, transmitting signals directly to the central nervous system (comprising the brain and spinal cord). As a result, it is thought that flavanol stimulation is transmitted via sensory nerves to activate the brain, subsequently inducing physiological responses in the periphery through the sympathetic nervous system” explains Dr. Fujii.

Flavanols trigger brain and stress responses

The team tested this idea in experiments using 10-week-old mice. The animals were given oral doses of flavanols at 25 mg/kg or 50 mg/kg of body weight, while a control group received only distilled water. Mice that consumed flavanols showed increased movement, more exploratory behavior, and stronger learning and memory performance than the controls.

Flavanol Induced Neural and Stress Pathways Diagram
A single oral administration of astringent FLs stimulated the central nervous system, activating the hypothalamic coricotropin-releasing hormone (CRH) neurons. The secreted CRH activated the noradrenaline (NA) neural network in the locus coeruleus (LC). The projection of NA from LC to the hypothalamus preoptic area suppresses sleep and promotes wakefulness. The projection of NA and dopamine (DA) from LC and DA from the ventral tegmental area to the hippocampus enhances memory. The projection of NA from LC to the brainstem activates sympathetic nerve activity, augmenting circulation and metabolism. Credit: Dr. Yasuyuki Fujii from Shibaura Institute of Technology

The researchers also observed heightened neurotransmitter activity in several parts of the brain. Levels of dopamine and its precursor levodopa, as well as norepinephrine and its metabolite normetanephrine, rose in the locus coeruleus–noradrenaline network shortly after administration.

These signaling molecules play central roles in motivation, attention, stress regulation, and alertness. In addition, key enzymes involved in producing noradrenaline (tyrosine hydroxylase and dopamine-β-hydroxylase) and transporting it (vesicular monoamine transporter 2) were increased, further boosting the activity of the noradrenergic system.

In addition, biochemical analysis revealed higher urinary levels of catecholamines—hormones released during stress—as well as increased activity in the hypothalamic paraventricular nucleus (PVN), a brain region central to stress regulation. Flavanol administration also boosted the expression of c-Fos (a key transcription factor) and corticotropin-releasing hormone in the PVN.

Implications for health and food design

Taken together, these results demonstrate that flavanol intake can trigger wide-ranging physiological responses resembling those induced by exercise—functioning as a moderate stressor that activates the central nervous system and enhances attention, arousal, and memory.

“Stress responses elicited by flavanols in this study are similar to those elicited by physical exercise. Thus, moderate intake of flavanols, despite their poor bioavailability, can improve the health and quality of life,” remarks Dr. Fujii.

These findings have potential implications in the field of sensory nutrition. In particular, next-generation foods can be developed based on the sensory properties, physiological effects, and palatability of foods.

Reference: “Astringent flavanol fires the locus-noradrenergic system, regulating neurobehavior and autonomic nerves” by Yasuyuki Fujii, Shu Taira, Keisuke Shinoda, Yuki Yamato, Kazuki Sakata, Orie Muta, Yuta Osada, Ashiyu Ono, Toshiya Matsushita, Mizuki Azumi, Hitomi Shikano, Keiko Abe, Vittorio Calabrese and Naomi Osakabe, 11 September 2025, Current Research in Food Science.
DOI: 10.1016/j.crfs.2025.101195

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