The same astringent dryness in the mouth that you might feel after consuming cocoa or berries could actually serve as a hidden stimulus for the brain. Flavanols, by activating sensory nerves, can trigger systems responsible for attention, memory, and stress response—essentially giving the brain a gentle workout.

What is an astringent sensation?

An astringent sensation is experienced as dryness, tightness, roughness, or even a sandpaper-like feeling in the mouth. This occurs when eating foods rich in certain plant compounds—polyphenols. Among these are flavanols, which have long been linked to a reduced risk of cardiovascular diseases. Cocoa, red wine, and berries are especially high in flavanols. Research shows that these substances may enhance memory, cognitive function, and protect brain cells from damage.

The flavanol mystery: how do they work?

Flavanols present a scientific puzzle, as only a small fraction of these compounds actually enter the bloodstream after digestion. Their low bioavailability raises the question: if the body absorbs so little, how do flavanols influence brain and nervous system function?

A new hypothesis: the role of taste

To unravel this phenomenon, researchers led by Dr. Yasuaki Fujii and Professor Naomi Osakabe from Shibaura Institute of Technology (Japan) focused on sensory perception. Their study, published in Current Research in Food Science, explored whether the distinctive astringent taste of flavanols could itself serve as a signal to the brain.

Dr. Fujii explains: “We hypothesized that the astringent taste of flavanols acts as a stimulus, sending signals directly to the central nervous system (including the brain and spinal cord). As a result, stimulation of sensory nerves by flavanols activates the brain, which then triggers physiological responses in the body via the sympathetic nervous system.”

Animal experiments

This hypothesis was tested on 10-week-old mice, which were given flavanols at doses of 25 or 50 mg/kg of body weight, while a control group received distilled water. Mice that received flavanols showed noticeably higher physical activity, explored their environment more, and performed better in learning and memory tasks compared to the control group.

Effects on the brain and neurotransmitters

Brain analysis revealed that flavanols increased neurotransmitter activity in various regions. Shortly after administration, levels of dopamine and its precursor levodopa, as well as noradrenaline and its metabolite normetanephrine in the locus coeruleus-noradrenaline system, rose. These substances play a key role in motivation, attention, alertness, and stress regulation. There was also an increase in the production of enzymes necessary for the synthesis and transport of noradrenaline, indicating enhanced signaling in this brain system.

Stress pathways and hormonal responses

Additional biochemical tests showed elevated levels of catecholamines in urine—hormones released during stress—as well as increased activity in the paraventricular nucleus (PVN) of the hypothalamus, which controls stress responses. Flavanol intake also raised levels of c-Fos (an important transcription factor) and corticotropin-releasing hormone in the PVN, further indicating activation of the brain’s stress pathways.

Effects similar to physical exercise

Overall, the results suggest that flavanols can trigger broad physiological responses similar to those seen with physical exercise. Rather than acting solely through absorption into the bloodstream, flavanols appear to serve as a mild stressor, stimulating the central nervous system and enhancing attention, alertness, and memory. As Dr. Fujii notes, “The stress responses triggered by flavanols are similar to those caused by physical exercise. Thus, moderate consumption of flavanols, despite their low bioavailability, may improve health and quality of life.”

Implications for sensory nutrition

These findings open new possibilities in the emerging field of sensory nutrition. By studying how foods are perceived and stimulate the nervous system, scientists suggest it may be possible to create a new generation of products that combine pleasant taste, beneficial physiological effects, and enhanced sensory appeal.