A study by Japanese researchers from the Shibaura Institute of Technology highlights how the astringent taste of flavanols — found in cocoa, tea, grapes, and berries — may help activate brain function and the nervous system by stimulating the gastrointestinal tract, despite lower bioavailability.
The authors note their insights suggest that foods’ sensory properties are important for promoting human health.
The team determined that flavanol intake in mice 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,” says lead researcher Dr. Yasuyuki Fujii.
“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.”
Direct signal to the brain
Astringency is a dry, puckering, rough, or sandpapery sensation in the mouth caused by plant-derived polyphenols. These bioactive compounds, including flavanols, are studied for their risk reduction in cardiovascular diseases.
The scientists experimented on 10-week-old mice, administering flavanols orally at doses of 25 mg/kg or 50 mg/kg body weight, while control mice received only distilled water.
Behavioral tests revealed that the flavanol-fed mice exhibited greater motor activity, exploratory behavior, and improved learning and memory compared to controls.
Immediately after the administration, flavanols enhanced neurotransmitter activity across several brain regions. Levels of dopamine, its precursor levodopa, norepinephrine, and its metabolite normetanephrine rose in the locus coeruleus–noradrenaline network. In the brain system, these chemicals regulate motivation, attention, stress response, and arousal.
Furthermore, enzymes that are critical for noradrenaline synthesis and transport were upregulated, which strengthened the signaling capacity of the noradrenergic system.
Clearing out stress hormones
Further biochemical analysis revealed flavanol administration led to 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.
Flavanols also boosted the expression of c-Fos (a key transcription factor) and corticotropin-releasing hormone in the PVN.
The 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.
The study findings are published in the journal Current Research in Food Science.
Separate research on flavanols published last month by a team in Birmingham, UK, found that these compounds may protect men’s vascular health during prolonged sitting. However, external experts cautioned that the study’s small sample size, short duration, and focus on healthy men limit its implications.
