The Science
Understanding the Systems We Work With
This page is provided for educational purposes. It summarises the biological systems relevant to WellThesis formulation directions — including the gut-brain axis, the microbiome, vagus nerve signalling, and metabolite biology. It does not constitute medical advice.
System Overview
The Gut-Brain Axis
The gut-brain axis refers to the bidirectional communication network connecting the central nervous system (CNS) with the enteric nervous system (ENS) and the gastrointestinal tract. This network is not a single pathway but an integrated system involving neural, endocrine, immune, and microbial components.
The enteric nervous system — sometimes described as the “second brain” — contains an estimated 100 to 500 million neurons embedded in the gut wall. It operates both autonomously and in constant dialogue with the brain via vagal, spinal, and humoral pathways.
Research across multiple disciplines has demonstrated associations between gut-brain axis function and outcomes spanning mood, cognition, stress responsiveness, immune regulation, and metabolic health. The direction and strength of causality in many of these associations remains an active area of investigation.
Key Communication Pathways
- Vagus nerve
Direct neural connection — carries signals in both directions between gut and brain
- HPA axis
Hypothalamic-pituitary-adrenal stress response pathway, modulated by gut signals
- Immune signalling
Cytokines and immune mediators produced in the gut acting systemically
- Enteroendocrine cells
Specialised gut cells secreting hormones including serotonin, GLP-1, and peptide YY
- Microbial metabolites
Short-chain fatty acids and other microbiome-derived compounds with systemic effects
Microbial Ecology
The Microbiome
The human gastrointestinal tract is home to an estimated 38 trillion microbial cells, comprising bacteria, archaea, fungi, viruses, and other microorganisms. This community — collectively referred to as the gut microbiome — is a complex ecosystem with significant individual variation in composition.
Microbial diversity is a feature of a healthy microbiome that appears consistently in research literature, with lower diversity associated — in epidemiological and observational studies — with a range of adverse health outcomes. The mechanisms underlying these associations are increasingly understood to involve metabolite production, immune education, barrier function, and direct neural signalling.
The microbiome is not static. It is shaped continuously by diet, physical activity, antibiotic exposure, stress, sleep quality, and ageing. This plasticity is scientifically significant: it suggests that environmental and dietary interventions may have meaningful effects on microbiome composition, though the clinical relevance of specific compositional changes remains an evolving area of research.
Emerging research suggests associations between microbiome composition and a broad range of physiological domains — including immune development, metabolic regulation, and neurological function. The direction and magnitude of causation in many cases remains uncertain; association should not be interpreted as mechanism without adequate supporting evidence.
Neural Signalling
The Vagus Nerve
The vagus nerve is the longest cranial nerve in the body and constitutes the primary neural component of the gut-brain axis. It is a mixed nerve carrying both afferent (gut to brain) and efferent (brain to gut) signals, with approximately 80% of its fibres being afferent — meaning most vagal traffic is from the gut upward.
Through vagal afferent pathways, the brain receives continuous information about the state of the gastrointestinal tract — including luminal content, stretch, inflammation, microbial metabolites, and enteroendocrine hormone levels. This information influences autonomic tone, feeding behaviour, mood regulation, and immune function.
Research into vagal tone — a measure of vagal activity — suggests associations with stress resilience, inflammatory regulation, and overall autonomic nervous system function. Emerging evidence from microbiome research indicates that microbial metabolites and signals may modulate vagal activity, though the clinical implications of this in humans require further investigation.
Vagal Signal Types
Afferent (gut → brain)
Mechanoreceptor signals (stretch, tension), chemoreceptor signals (nutrients, pH, microbial products), and enteroendocrine hormone detection. Accounts for ~80% of vagal fibres.
Efferent (brain → gut)
Parasympathetic motor signals regulating gut motility, secretion, mucosal immune function, and intestinal blood flow. The cholinergic anti-inflammatory pathway operates via this route.
Biochemistry
Metabolites and Signalling Molecules
Short-Chain Fatty Acids
SCFAs — including butyrate, propionate, and acetate — are produced by microbial fermentation of dietary fibre. They serve as an energy source for colonocytes, regulate gut barrier integrity, modulate immune function, and emerging evidence suggests systemic and neurological effects via multiple pathways.
Neurotransmitter Precursors
An estimated 90–95% of the body's serotonin is synthesised in the gut by enterochromaffin cells. Tryptophan, the dietary precursor to serotonin, is also metabolised via the kynurenine pathway, producing neuroactive compounds. The gut microbiome influences these metabolic routes in ways that are actively studied.
Immune Modulation
The gut is the body's largest immune organ. Microbial signals, structural components, and metabolites play significant roles in educating and regulating the mucosal immune system, with systemic implications for inflammatory tone. Dysregulation of gut immune function is implicated in both intestinal and extra-intestinal conditions.
Systemic Connections
Stress, Cognition, and Metabolism
Research across epidemiology, animal models, and clinical studies has identified associations between gut microbiome composition and outcomes spanning psychological stress resilience, cognitive function, and metabolic parameters. It is important to distinguish between association and causation: observational associations between microbiome states and health outcomes do not, on their own, establish a causal mechanism.
Where mechanistic evidence exists — particularly from well-designed randomised controlled trials — the picture is more compelling. Certain probiotic strains, for example, have been studied in the context of HPA axis reactivity, stress-related gastrointestinal symptoms, and cognitive performance, with results that vary by strain, dose, population, and outcome measure.
The intersection of gut biology and metabolic health is another area of significant research interest, with emerging evidence implicating the microbiome in insulin sensitivity, GLP-1 secretion, lipid metabolism, and energy regulation. These associations are biologically plausible given the role of microbial metabolites and the ENS in regulating host metabolism, though the clinical translation of these findings is still developing.
We engage with this body of research carefully — taking seriously what the evidence supports while being transparent about what it does not yet establish.
How We Evaluate Evidence
Our Scientific Framework
Every formulation direction is evaluated against ten criteria. No single criterion is sufficient on its own — the framework is designed to surface the full complexity of moving from scientific evidence to a manufacturable, safe, and claim-appropriate product.
Biological Rationale
Is there a credible, mechanistic basis for the ingredient's proposed action in the relevant biological system?
Evidence Quality
What is the strength, consistency, and applicability of the existing research — preclinical, clinical, or observational?
Safety Profile
What is the documented safety record at the proposed dose, including contraindications and drug interactions?
Dose Feasibility
Can an effective and safe dose be incorporated into a commercially viable product format?
Ingredient Compatibility
Do the ingredients in a formulation interact in ways that affect efficacy, safety, or stability?
Stability
Does the ingredient remain stable across the product's intended shelf life and storage conditions?
Delivery & Bioavailability
Does the delivery format support adequate absorption and bioavailability of the active compound?
Manufacturing Repeatability
Can the formulation be produced consistently at scale to meet the specification the evidence supports?
Regulatory Suitability
Is the ingredient and associated claim appropriate under the regulatory frameworks of target markets?
Real-World Experience
Is there meaningful real-world use data, consumer reports, or clinical practice observation to complement research findings?
The information on this page is for educational purposes and does not constitute medical or clinical advice. Individual circumstances vary. Consult a qualified healthcare professional before making any health-related decisions.