The Host Capacity Model: A Systems Biology Framework for Chronic Illness
A unifying framework for SIBO, MCAS, POTS, post-COVID illness, and hEDS overlap — built on colonocyte bioenergetics, NAD+ metabolism, and the dysbiosis cascade.
The paradigm shift
Modern medicine treats disease as something that happens to you — infection occurs, dysbiosis develops, inflammation activates. Therapeutic goal: kill the pathogens, suppress the symptoms, manage the disease. This model fails for chronic illness.
Chronic illness isn't an accident. It's a failure of the body's host capacity — its ability to maintain a healthy internal ecosystem. The Host Capacity Model inverts the paradigm: disease arises from failure of the host to suppress dysbiosis, maintain barriers, and regulate inflammation. Cure disease by restoring the host.
Principle 1: The host determines microbial ecology
Bacteria don't decide to overgrow. They grow when the host environment allows it. Standard model: bacteria overgrow → cause dysbiosis → cause disease. Host Capacity Model: host barrier function fails (colonocyte bioenergetic failure) → dysbiotic bacteria exploit the weakened environment → dysbiosis is downstream, not upstream. Killing bacteria without restoring host capacity guarantees recurrence. Restore host capacity, and dysbiosis resolves even without antimicrobials.
Principle 2: Colonocyte bioenergetics are the foundation
Colonocytes are your gut's immune and barrier system. They depend entirely on mitochondrial ATP for tight junction maintenance (claudins, ZO-1), mucus synthesis and secretion (goblet cells), antimicrobial peptide production (Paneth cells), metabolite signaling to feed beneficial bacteria, and barrier function — the primary defense against dysbiosis. When mitochondrial function fails, usually from NAD+ depletion driven by chronic CD38 activation, all of these collapse simultaneously. The energy deficit is the primary lesion. Everything else is downstream.
Principle 3: NAD+ depletion is the key bottleneck
NAD+ is the electron carrier for all cellular energy production. It cycles between NAD+ (energy extraction in the Krebs cycle) and NADH (energy regeneration in the electron transport chain). When NAD+ is depleted, the Krebs cycle slows, electron transport stalls, cells can't produce ATP, colonocytes fail, dysbiosis establishes.
Why NAD+ depletes: CD38 activation from chronic inflammation converts NAD+ to inactive ADP-ribose; PARP overactivation from DNA damage consumes NAD+ for repair; SIRT3 cannot function when NAD+ is low, leading to loss of mitochondrial acetylation control. The result is a vicious cycle where inflammation consumes NAD+, which worsens mitochondrial function, which perpetuates inflammation.
Principle 4: Energy failure cascades into dysbiosis
The cascade is mechanical, not mysterious. NAD+ depletes → colonocyte ATP production drops → tight junctions collapse, mucus thins, antimicrobial defenses decline → barrier breaks down, LPS translocates, dysbiotic bacteria exploit the environment → dysbiotic metabolites (H₂S, D-lactate, secondary bile acids) perpetuate inflammation → inflammation perpetuates NAD+ depletion. Chronic dysbiosis-driven illness persists despite antimicrobials because host capacity never recovered.
Principle 5: Barrier failure drives multisystem disease
When the intestinal barrier fails, LPS translocation activates TLR4 and drives systemic inflammation. Dysbiotic metabolites enter circulation, producing brain fog, fatigue, pain, and MCAS activation. Increased permeability triggers immune activation against food antigens (food sensitivities) and dysbiotic bacterial antigens via molecular mimicry (autoimmunity). "Leaky gut" matters not just for intestinal symptoms but for systemic disease perpetuation.
The model applied to major chronic conditions
SIBO. Standard view: bacteria overgrew, kill them. Host Capacity view: colonocyte energy failure allowed dysbiosis to establish in the small intestine. Restore bioenergetics, suppress dysbiosis, restore barrier — dysbiosis resolves.
MCAS. Standard view: mast cells are hyperreactive. Host Capacity view: in dysbiosis-driven MCAS, dysbiotic metabolites (especially H₂S) trigger mast cells. The primary lesion is dysbiosis. Treat dysbiosis and MCAS resolves.
POTS. Standard view: autonomic dysfunction; volume expansion and salt. Host Capacity view: POTS is often secondary to endothelial mitochondrial dysfunction. Restore endothelial NAD+, address dysbiosis-driven endotoxemia, manage symptoms.
Post-COVID illness. Standard view: lingering viral effects. Host Capacity view: SARS-CoV-2 damaged mitochondrial Complex I/III in multiple cell types, driving NAD+ depletion, dysbiosis, barrier breakdown, and inflammation. The disease is the mitochondrial aftermath, not the virus. Intensive NAD+ restoration is primary.
The four-phase recovery model
All chronic illnesses following this framework use the same structure. Phase 1: assessment — measure the bioenergetic deficit (OAT, NAD+), identify dysbiotic profile (metagenomics, SCFA), assess barrier (zonulin, calprotectin), quantify inflammation (hs-CRP, LPS/LBP). Phase 2: mapping — understand which pathways are blocked, which species dominate, how severe barrier breakdown is, how findings correlate with clinical presentation. Phase 3: restoration — restore bioenergetic capacity (NAD+, mitochondrial cofactors), suppress dysbiosis (antimicrobials, dietary restriction), restore barrier (butyrate, L-glutamine, mucosal healing), manage symptoms during recovery. Phase 4: prevention — sustain bioenergetic recovery (long-term NAD+ maintenance), prevent dysbiosis recurrence (probiotics, resistant starch, healthy diet), maintain barrier integrity, monitor for recurrence signals.
Where to start
If you have a specific condition, start with the corresponding mechanistic framework: SIBO protocol, MCAS stratification, dysbiosis treatment, post-COVID gut dysfunction, or the hEDS/POTS/MCAS overlap. If your case is complex or multisystem, request a consultation to map your specific bioenergetic and dysbiosis profile.