Creative Touch Permanent Makeup and Aesthetics

The gut microbiome is the community of approximately 100 trillion microorganisms – bacteria, fungi, archaea, and viruses – resident principally in the large intestine, whose collective metabolic activity functions as a regulatory system with effects that extend well beyond digestion. Microbiome composition determines whether the gut produces protective metabolites that support barrier integrity, immune tolerance, and metabolic balance, or whether it generates pro-inflammatory signals – principally lipopolysaccharide – that drive systemic low-grade inflammation. The balance between these two outputs is now recognised as a meaningful contributor to skin health, metabolic function, immune regulation, and neurological signalling, operating through mechanisms that are distinct from, but interact with, every major axis of systemic homeostasis.

The gut microbiome is not a passive collection of digestive organisms – it is a metabolically active system that produces compounds, modulates immune responses, and communicates with the brain, liver, skin, and endocrine system through multiple parallel channels. The dominant bacterial phyla in a healthy microbiome are Firmicutes and Bacteroidetes, with ecologically important species including Faecalibacterium prausnitzii, Akkermansia muciniphila, Bifidobacterium species, and Roseburia species playing particularly well-documented protective roles. F. prausnitzii constitutes approximately 4% of the luminal microbiota in healthy individuals, and its depletion is associated with chronic intestinal inflammation and reduced SCFA output; A. muciniphila is strongly associated with healthy metabolic function, and both species are considered leading next-generation probiotic candidates. ^[5]

Diversity – the number and relative balance of distinct species – is the conventional proxy for microbiome resilience, but functional output is the more clinically meaningful measure: a microbiome can appear diverse on sequencing whilst producing inadequate quantities of protective metabolites, and conversely, a lower-diversity microbiome maintained on whole-food animal-based diets may retain functional output that diversity metrics alone would underestimate.

The microbiome’s systemic influence operates through four principal routes: production of short-chain fatty acids (SCFAs) that support immune regulation and gut barrier integrity; production of tryptophan-derived indole metabolites – principally indole-3-propionic acid (IPA) – that directly protect tight junction architecture; generation of LPS from gram-negative bacterial outer membranes when dysbiosis increases their relative abundance; and modulation of enteroendocrine signalling, including glucagon-like peptide-1 (GLP-1) output from colonic L-cells. Each route operates simultaneously, and the net systemic effect depends on which is dominant.

What Disrupts the Microbiome – Dysbiosis Drivers

Dysbiosis – a shift in microbiome composition away from commensal-dominant towards a higher relative proportion of gram-negative and pathobiont species – is not driven by any single dietary or lifestyle factor. The most consistently evidenced drivers are:

• Ultra-processed food additives – emulsifiers including carboxymethylcellulose (CMC) and polysorbate 80 (P80) directly disrupt the intestinal mucus layer and alter microbiome composition in ways that increase the pro-inflammatory potential of the microbial community. Human microbiome model research published in Gut demonstrated that both CMC and P80 act directly upon the microbiota – independently of host inflammation – increasing LPS and pro-inflammatory flagellin production; transfer of the emulsifier-treated microbiome to germ-free mice recapitulated low-grade inflammation and metabolic dysregulation. More recent in vitro work confirms that CMC diminishes epithelial integrity specifically through its interaction with the microbiome rather than direct epithelial contact, underscoring that the harm mechanism runs through microbial disruption. Artificial sweeteners including saccharin and sucralose alter microbial composition and reduce SCFA-producing species in human trials. The mechanism of harm is in the additives, not fibre displacement – a low-UPF diet of any macronutrient composition removes this additive exposure. ^[2]

• Antibiotic exposure – broad-spectrum antibiotics deplete commensal populations indiscriminately; recovery of pre-antibiotic diversity may take months and is incomplete in some individuals, with repeated courses compounding the disruption.

• Chronic psychological stress – HPA axis activation drives microbiome disruption through multiple routes: cortisol alters gut motility and mucosal immune function; CRH acts directly on intestinal mast cells via CRH-R1 and CRH-R2 receptors, increasing macromolecular intestinal permeability independently of the LPS pathway. A human colonic biopsy study published in Gut confirmed that CRH challenge measurably increased mucosal permeability through CRH receptor subtypes on subepithelial mast cells; this effect was abolished by mast cell stabilisation, confirming the mast cell as the operative mechanism. The gut microbiome is therefore directly responsive to psychological state, not merely to diet. ^[11]

• High sugar intake – promotes rapid growth of fermentative and pathobiont species at the expense of slower-growing commensals, shifting the ecological balance independent of additive exposure.

A note on dietary fibre: dietary fibre is the primary fermentation substrate for SCFA-producing bacteria, and its presence consistently supports butyrate-producing species. However, the evidence does not support fibre absence as the primary driver of dysbiosis in otherwise whole-food diets – whole food quality and absence of disruptive additives and excess sugar appear to be the consistent protective factors across dietary patterns, including low-fibre animal-based diets in emerging research.

The Three Routes to Gut-Protective SCFAs

SCFAs – principally butyrate, propionate, and acetate – are the primary protective output of a healthy gut microbiome, supporting gut epithelial integrity, reducing intestinal permeability, and regulating systemic immune function. Butyrate is the primary energy source for colonocytes, and its barrier-protective effect is mechanistically established: butyrate increases transepithelial electrical resistance (TEER) in colonocyte monolayers by facilitating tight junction assembly via AMPK activation, a finding confirmed in human cell line research. The mainstream narrative positions dietary fibre as the singular route to SCFA production, but three distinct routes exist: ^[8]

1. Dietary fibre fermentation – Bifidobacterium, Lactobacillus, F. prausnitzii, and Roseburia species ferment indigestible dietary fibre to produce butyrate, propionate, and acetate. This is the best-evidenced route and most consistently studied. Its depletion from butyrate-producing species is directly associated with epithelial barrier deterioration and increased intestinal permeability. ^[13]

2. Pre-formed dietary butyrate – ruminant dairy fat – butter, cream, and aged cheese – contains butyrate directly in its triglyceride structure as tributyrin, which is hydrolysed to free butyrate by pancreatic lipases and delivered to the colon without requiring microbial fermentation. In vitro upper gastrointestinal simulations have shown that tributyrin is substantially resistant to gastric acid, with a meaningful proportion remaining stable through to the large intestine where it supports barrier function and increases Bifidobacterium spp. and A. muciniphila abundance. This route is independent of microbiome composition and dietary fibre intake, and is not accounted for in fibre-centric SCFA discussions. ^[3]

3. Fermented foods – kimchi, kefir, sauerkraut, yoghurt, and aged cheese provide direct inoculation of live bacteria alongside SCFA precursors and short-chain organic acids produced during fermentation. A 2021 Stanford RCT (n=36, 10 weeks) demonstrated that a high-fermented-food diet significantly increased microbiome diversity and reduced 19 markers of systemic inflammation; by contrast, none of these inflammatory markers decreased in the high-fibre diet group over the same period, and microbiome diversity in the fibre group remained stable. The fermented food benefit operates through a mechanism that does not depend on the host’s existing microbial capacity to ferment fibre substrates – a practically meaningful distinction for clients whose baseline microbiome may be depleted. ^[12]

The practical implication is that whole-food dietary quality – whether plant-rich, animal-based, or mixed – is the consistent driver of SCFA availability when combined with appropriate fermented food intake and avoidance of disruptive additives.

LPS, Intestinal Permeability, and Metabolic Endotoxaemia

When dysbiosis increases the relative proportion of gram-negative bacteria, the total LPS burden in the gut rises. LPS is a structural component of gram-negative bacterial outer membranes – its presence is normal; its systemic translocation is not. Increased intestinal permeability – driven by tight junction dysfunction from SCFA depletion, direct additive disruption of the mucus layer, or CRH-driven mast cell degranulation – allows LPS to translocate into portal and then systemic circulation, a state termed metabolic endotoxaemia.

Systemic LPS binds Toll-Like Receptor 4 (TLR4) on macrophages, endothelial cells, and adipocytes, activating NF-κB signalling and driving production of TNF-α, IL-1β, and IL-6 – the same cytokine profile that characterises inflammageing. Metabolic endotoxaemia is robustly documented in obesity and type 2 diabetes, where circulating LPS concentrations are measurably elevated – one review of the clinical literature found plasma LPS concentrations approximately 76% higher in patients with T2DM compared to healthy controls, correlating with inflammatory marker burden. Its relevance in otherwise healthy individuals consuming Western diets is mechanistically plausible and consistent with the evidence, though the magnitude of effect in non-obese, non-diabetic populations warrants appropriately calibrated claims. ^[7]

The concept of increased intestinal permeability – sometimes referred to in lay contexts as “leaky gut” – is mechanistically sound and well-evidenced in IBD and coeliac disease, where tight junction disruption is histologically confirmed and clinically significant. Extrapolation to healthy non-IBD populations, where dietary factors produce measurable systemic inflammation, is supported by mechanistic plausibility but is more contested in the clinical literature than the mainstream wellness narrative typically acknowledges. The LPS/TLR4 pathway itself, however, is not in dispute. ^[7]

Tryptophan Metabolism – The IPA:Kynurenine Balance

Tryptophan metabolism represents one of the more recently appreciated functional intersections between the gut microbiome, immune activation, metabolic health, and neurological signalling. Dietary tryptophan is metabolised through two competing pathways whose relative balance reflects the functional state of the microbiome and the systemic inflammatory environment simultaneously.

The IPA pathway – commensal gut bacteria, principally Clostridium sporogenes, convert dietary tryptophan to IPA. IPA binds the pregnane X receptor (PXR) on intestinal epithelial cells, upregulating tight junction proteins including claudin-1, occludin, and ZO-1, and directly protecting gut barrier integrity. Research using human colonic epithelial cell models confirmed that IPA (at concentrations ≥0.5 mM) measurably increased TEER, upregulated claudin-1, occludin, and ZO-1 expression, inhibited LPS-induced apoptosis, and suppressed pro-inflammatory cytokine release (IL-1β, IL-6, TNF-α) through the TLR4/NF-κB pathway – a dual physical barrier and anti-inflammatory action from a single microbial metabolite. Additionally, IPA strengthened the mucus barrier by increasing MUC2 and MUC4 mucin production. Critically, IPA cannot be synthesised endogenously – its blood concentration is entirely dependent on commensal bacterial activity, making it a direct functional marker of microbiome health rather than a dietary intake measure. ^[4]

The kynurenine pathway – when immune activation increases, the enzyme indoleamine 2,3-dioxygenase (IDO) – upregulated by LPS, IFN-γ, and TNF-α – diverts tryptophan away from the IPA pathway towards kynurenine (KYN) production. A separate rate-limiting enzyme, tryptophan 2,3-dioxygenase (TDO), is activated specifically by glucocorticoids, providing a direct stress-responsive route into the kynurenine pathway that is independent of gut-derived LPS. Elevated circulating KYN:TRP ratio is an established marker of IDO/TDO-driven immune activation, measurably elevated in chronic inflammatory states, metabolic disease, and chronic psychological stress. ^[6]

The consequence of kynurenine pathway dominance extends beyond immune activation. Tryptophan is also the precursor for serotonin synthesis in gut enterochromaffin cells – the source of approximately 95% of the body’s serotonin. When IDO/TDO activation diverts tryptophan to kynurenine, serotonin substrate availability is reduced simultaneously, providing a direct biochemical mechanism linking gut dysbiosis and systemic inflammation to the altered mood and gut-brain signalling documented in the gut-brain axis literature. This mechanism is developed further in the ENS entity.

Higher IPA concentrations have been associated with greater insulin sensitivity, improved metabolic flexibility, and reduced inflammatory burden in human cohort data – establishing a connection between gut microbiome functional output and the metabolic health outcomes addressed in the T2DM entity. The IPA:KYN balance therefore provides a single functional readout that simultaneously captures gut barrier competency, immune activation state, metabolic health orientation, and stress axis activity.

Clinical Pearl IPA:KYN ratio cannot be inferred from diversity sequencing alone – a client with apparently normal microbiome diversity may show IDO-driven kynurenine dominance if their systemic inflammatory burden or chronic stress is elevated. Functional tryptophan metabolite profiling captures what sequencing does not.

The Microbiome–GLP-1 Connection (Emerging Evidence)

GLP-1 is produced not only in the ileal L-cells that mediate the ileal brake response, but also by L-cells distributed throughout the colon – a distribution that places GLP-1 output directly within the microbial environment. A. muciniphila has been specifically associated with improved GLP-1 secretion; in vitro research using human NCI-H716 L-cells demonstrated that A. muciniphila cell extracts induced a robust, dose-dependent increase in GLP-1 secretion, with the highest concentrations achieving over 2,000% greater secretion compared to negative controls – a magnitude comparable to glutamine, a well-characterised GLP-1 secretagogue. ^[1]

This creates a plausible mechanistic bridge from microbiome composition → colonic GLP-1 output → satiety signalling → metabolic regulation that extends the GLP-1 story beyond ileal brake pharmacology. This is an active and rapidly developing research area; the current evidence base is in vitro and early clinical, and is sufficient to establish the connection as scientifically credible, but not yet sufficient to make specific clinical claims about microbiome interventions as a route to GLP-1 augmentation in human practice. The GLP-1 and Ileal Brake entity carries the primary pharmacological detail; this connection is flagged here for completeness and will be updated as the evidence matures. ^[1]