The distinctive astringency – the dry, puckering sensation – experienced when eating cocoa, red wine, or berries may do more than simply affect taste. New research suggests this sensation can directly stimulate the brain, potentially enhancing alertness, focus, and memory. This surprising finding challenges conventional nutritional thinking, which typically focuses on the bioavailability – how much of a substance is absorbed into the bloodstream – of beneficial compounds.
For years, flavanols, the plant-derived polyphenols responsible for this astringency, have been linked to positive health outcomes, including reduced risk of cardiovascular disease and improved cognitive function. However, the limited amount of flavanols that actually enter circulation after consumption has puzzled scientists. How could these compounds exert such noticeable effects on the brain if so little is absorbed?
Researchers at the Shibaura Institute of Technology in Japan, led by Dr. Yasuyuki Fujii and Professor Naomi Osakabe, proposed a novel explanation: the sensation of astringency itself might be the key. Their study, published in Current Research in Food Science, investigated whether the taste of flavanols could directly signal the brain, triggering physiological responses.
“Flavanols exhibit an astringent taste. We hypothesized that this taste serves as a stimulus, transmitting signals directly to the central nervous system,” explained Dr. Fujii. “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.”
To test this hypothesis, the team conducted experiments on mice. They administered flavanol solutions at doses of 25 mg/kg or 50 mg/kg of body weight to one group, while a control group received distilled water. The results were striking. Mice that consumed flavanols exhibited increased physical activity, greater exploratory behavior, and improved performance on learning and memory tasks compared to the control group.
Further analysis revealed significant changes in brain activity. Shortly after flavanol administration, levels of dopamine and its precursor, levodopa, increased, alongside norepinephrine and its metabolite normetanephrine, specifically within the locus coeruleus-noradrenaline network. This network is crucial for regulating motivation, attention, alertness, and the body’s stress response. The researchers also observed increased production of enzymes vital for norepinephrine synthesis and transport, suggesting enhanced signaling within this brain system.
The effects extended beyond neurotransmitter activity. Biochemical tests showed elevated levels of catecholamines in the mice’s urine – hormones released during stress – and increased activity in the hypothalamic paraventricular nucleus (PVN), a brain region central to controlling stress responses. Levels of c-Fos, a key transcription factor, and corticotropin-releasing hormone also rose in the PVN, further confirming activation of stress-related brain pathways.
Interestingly, the observed physiological responses closely resembled those triggered by physical exercise. This suggests that flavanols, rather than relying on absorption into the bloodstream, function as a mild stressor, stimulating the central nervous system and leading to heightened attention, alertness, and memory. “Stress responses elicited by flavanols in this study are similar to those elicited by physical exercise,” Dr. Fujii noted. “moderate intake of flavanols, despite their poor bioavailability, can improve the health and quality of life.”
These findings contribute to the growing field of sensory nutrition, which explores how the sensory properties of food – taste, smell, texture – can influence brain and body function. The research suggests that it may be possible to develop foods that not only provide nutritional value but also directly stimulate the nervous system, offering a novel approach to enhancing cognitive performance and overall well-being.
While this study was conducted on mice, the implications for human health are significant. The research highlights the potential for harnessing the sensory impact of foods to promote brain health, even in cases where absorption of key compounds is limited. Further research is needed to confirm these findings in humans and to explore the optimal levels of flavanol intake for maximizing cognitive benefits. However, the current evidence suggests that enjoying a piece of dark chocolate or a handful of berries may offer more than just a pleasant taste experience – it could be a subtle, yet powerful, boost for the brain.
This work was supported by JSPS KAKENHI (Grant Number 23H02166).
