FASTING, THE GUT-BRAIN AXIS
New Insights from the Inaugural Psychoneuroimmunology Congress
Recently, our scientific director Dr Robin Mesnage spoke at the First International Congress of the Scientific Society of Psychoneuroimmunology in Granada on 14 November 2025, an event that brought together researchers working across neuroscience, immunity and metabolism. The congress highlighted how closely our biological systems communicate with one another, and how tools such as structured fasting can positively influence these connections supported by modern science.
Fasting has long been recognised as one of the most reliable longevity tools observed across species. From simple organisms to mammals, reducing nutrient intake in a structured and rhythmic way can extend lifespan, improve metabolic flexibility and switch on deep cellular repair processes. These shifts often begin in the gut, one of the body’s busiest metabolic and immune hubs, and then extend into the immune and nervous systems. This whole-body perspective helps explain how nutrition affects the gut-brain axis and shapes communication throughout the body.
The gut as a metabolic and immune hub
The gut is home to a vast microbial ecosystem, dense immune tissue and the enteric nervous system, sometimes described as a second brain. When food intake shifts during fasting, this environment changes quickly. Microbial communities start to reorganise, digestion slows and the gut lining begins natural repair processes.
These shifts also affect immunity. Roughly 70% of the body’s immune cells sit in or around the gut, and they constantly monitor the microbial and dietary landscape. As this environment changes during fasting, immune activity adjusts too, helping to regulate inflammation throughout the body.
During fasting, immune activity begins to recalibrate. Studies in animals and humans show reductions in inflammatory markers in those who start with higher inflammation and shifts towards greater metabolic balance in people with chronic immune activation. These adaptive responses are central to the field of psychoneuroimmunology, the field that explores how the immune system influences brain function and behaviour.
The gut-brain axis in fasting
The gut-brain axis is the two-way communication system between the intestine and the brain, which works through nerve pathways, immune signals and chemicals made by gut microbes. When fasting changes gut activity, these messages change as well. Certain microbes that do well during fasting make helpful short chain fatty acids and other compounds that can interact with the brain. At the same time, calmer immune activity in the gut leads to fewer inflammatory signals that can affect mood, thinking and stress levels. Instead of acting on just one part of the body, fasting seems to create a coordinated reset across several connected systems.
The oral microbiome and the brain: a neglected connection
The oral microbiome, the community of microorganisms in the mouth, plays an important role in cardiovascular and mental health, yet it is often overlooked.
Recent research shows that certain sulphur producing bacteria in the mouth can influence inflammation, and that fasting shifts the balance of these salivary microbes. This suggests that fasting may reshape the mouth’s microbial environment in a way that supports wider metabolic and immune changes, complementing its effects on the gut. These shifts may have downstream effects on whole body inflammation and on processes linked to brain health.
The mouth and gut form a continuous tract that is constantly communicating with both the immune system and the brain. Looking at them together gives a clearer picture of how fasting may influence health across several connected systems.
Connecting the dots
The emerging field of psychoneuroimmunology highlights that the body works as a connected whole rather than in separate parts. When metabolism, immunity and brain function are viewed together, patterns that once seemed complex become easier to understand.
The congress in Granada introduced this integrative field and explored how lifestyle factors, including diet, shape the communication between the gut, the immune system and the brain.
Within this context, fasting stands out as a particularly powerful example. It shows how one dietary change can influence several systems at once, from shifts in microbial communities to steadier immune signals and changes in neural pathways. Together, these coordinated responses suggest that fasting may help support healthy communication across the body’s major regulatory networks.
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