However, flavanols present a scientific puzzle. Only a small portion of what people consume actually makes it into the bloodstream after digestion. This low bioavailability raises an important question: if so little is absorbed, how do flavanols still appear to influence brain function and the nervous system?

A New Hypothesis Focused on Taste

To explore this mystery, researchers led by Dr. Yasuyuki Fujii and Professor Naomi Osakabe at Shibaura Institute of Technology in Japan turned their attention to sensory perception. Their study, published in Current Research in Food Science, examined whether the distinctive astringent taste of flavanols could itself act as a signal to the brain.

“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.

Testing Flavanols in Animal Experiments

The team tested this idea using 10-week-old mice. The animals received oral doses of flavanols at 25 mg/kg or 50 mg/kg of body weight, while a control group was given distilled water. The mice that consumed flavanols showed noticeably higher levels of physical activity, increased exploration, and stronger performance in learning and memory tasks compared with the control group.

Brain analysis revealed that flavanols boosted neurotransmitter activity in multiple regions. Shortly after administration, levels of dopamine and its precursor levodopa increased, along with norepinephrine and its metabolite normetanephrine in the locus coeruleus-noradrenaline network. These chemicals play key roles in motivation, attention, alertness, and stress regulation. The researchers also observed increased production of enzymes essential for norepinephrine synthesis (tyrosine hydroxylase and dopamine-β-hydroxylase) and transport (vesicular monoamine transporter 2), suggesting stronger signaling within this brain system.

Stress Pathways and Hormone Responses

Additional biochemical tests showed higher levels of catecholamines in urine, which are hormones released during stress, along with increased activity in the hypothalamic paraventricular nucleus (PVN). This brain region is central to controlling stress responses. Flavanol intake also raised levels of c-Fos (a key transcription factor) and corticotropin-releasing hormone in the PVN, further indicating activation of stress-related brain pathways.

Effects That Resemble Exercise

When viewed together, the findings suggest that flavanols can trigger broad physiological responses similar to those produced by physical exercise. Rather than acting only through absorption into the bloodstream, flavanols appear to function as a moderate stressor that stimulates the central nervous system, leading to heightened attention, alertness, 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.

Implications for Sensory Nutrition

The results point to new possibilities in the emerging field of sensory nutrition. By focusing on how foods feel and stimulate the nervous system, researchers suggest it may be possible to design next-generation foods that combine appealing taste, beneficial physiological effects, and improved palatability.

This work was supported by JSPS KAKENHI (Grant Number 23H02166).