Gut Health — Advanced Guide

Advanced Gut Health Topics

Leaky Gut and Intestinal Permeability

INTESTINAL BARRIER FUNCTION:
  Single layer of epithelial cells connected by tight junctions
  Allows: nutrients through | Blocks: pathogens, undigested food, toxins
  
  Leaky gut (increased intestinal permeability):
    Tight junctions become loose
    Undigested food particles, bacteria, toxins enter bloodstream
    Triggers systemic inflammation and immune response
  
  CAUSES OF LEAKY GUT:
    Dysbiosis: overgrowth of harmful bacteria
    Diet: excessive refined sugar, processed food, alcohol, gluten (in sensitive)
    NSAIDs: ibuprofen, aspirin damage gut lining
    Stress: cortisol disrupts epithelial tight junctions
    Antibiotics: kill beneficial bacteria, allow pathogen overgrowth
  
  HEALING STRATEGIES:
    Remove triggers: processed food, alcohol, food intolerances
    Replace: digestive enzymes, HCl if deficient
    Reinoculate: probiotics + fermented foods
    Repair: L-glutamine (gut cell fuel), zinc, collagen, bone broth
    Rebalance: stress management, sleep optimisation
  
  CONDITIONS LINKED TO DYSBIOSIS:
    IBS, IBD (Crohn's, UC), coeliac disease
    Type 2 diabetes, obesity
    Mental health: depression, anxiety
    Autoimmune: rheumatoid arthritis, thyroid disease
    Skin: eczema, psoriasis, acne

SIBO (Small Intestinal Bacterial Overgrowth):
  Bacteria from large intestine colonise small intestine
  Symptoms: bloating (especially after meals), gas, diarrhoea, malabsorption
  Diagnosis: hydrogen/methane breath test
  Treatment: specific antibiotics (rifaximin) + diet + address root cause

The Gut and Immunity

GUT IMMUNE SYSTEM:
  GALT (Gut-Associated Lymphoid Tissue): 70% of immune system
  Peyer's patches: lymphoid tissue sampling gut contents
  IgA secretion: first-line antibody defence in gut lumen
  Gut bacteria educate immune system — particularly in early life
  
MICROBIOME AND DISEASE:
  Obese microbiome: more Firmicutes (extract more calories from food)
  Lean microbiome: more Bacteroidetes
  Transplanting obese mouse microbiome → lean mouse gains weight
  
BENEFICIAL BACTERIA:
  Lactobacillus: ferment lactose, produce lactic acid, inhibit pathogens
  Bifidobacterium: produce short-chain fatty acids, support immunity
  Akkermansia muciniphila: maintain gut lining, metabolic health marker
  Faecalibacterium prausnitzii: anti-inflammatory, reduced in IBD
  
SHORT-CHAIN FATTY ACIDS (SCFAs):
  Produced when gut bacteria ferment dietary fibre
  Butyrate: fuel for colonocytes, anti-inflammatory, reduce colon cancer risk
  Propionate: liver metabolism, appetite regulation
  Acetate: energy substrate, immune regulation

Revision Notes

LEAKY GUT: tight junctions loosen → inflammation → autoimmune/systemic issues
4Rs: Remove (triggers) → Replace (enzymes) → Reinoculate (probiotics) → Repair (glutamine)
SIBO: bacteria in small intestine | bloating after meals | breath test diagnosis
GALT: 70% immune system in gut | IgA first-line defence
SCFAs: butyrate (gut fuel) + propionate + acetate — produced from fibre fermentation
FIRMICUTES: more in obese | BACTEROIDETES: more in lean — diet shapes ratio