Gut Health — Key Concepts and Q&A
Core Concepts
Q: The gut microbiome — what is it and why does it matter?
The gut microbiome is the community of trillions of microorganisms (bacteria, fungi, viruses, archaea) living primarily in the large intestine. Each person's microbiome is as unique as a fingerprint.
Functions of gut bacteria:
•Digest fibre → produce Short-Chain Fatty Acids (SCFAs: butyrate, propionate, acetate) — energy for gut lining cells, anti-inflammatory
•Synthesise vitamins: B12, K2, some B vitamins
•Regulate immune system: ~70% of immune cells are in the gut
•Produce neurotransmitters: 90% of serotonin made in gut (gut-brain axis)
•Protect against pathogens: competitive exclusion, produce antimicrobial compounds
•Metabolise drugs and toxins
Dysbiosis: Imbalance in gut microbiome composition — associated with IBS, inflammatory bowel disease, obesity, type 2 diabetes, depression, autoimmune conditions.
Q: What harms the gut microbiome?
•Antibiotics: Kill beneficial bacteria along with pathogens. Microbiome may take weeks-months to recover.
•Ultra-processed food: High sugar, refined starch, artificial emulsifiers, preservatives — feeds harmful bacteria, reduces diversity.
•Chronic stress: Gut-brain axis — stress alters gut motility, permeability, and microbiome composition.
•Alcohol: Disrupts microbiome balance, damages gut lining at high intake.
•Low fibre diet: Starves beneficial bacteria. Western diet → 40% less diversity than traditional diets.
•Unnecessary medications: NSAIDs (ibuprofen) damage gut lining. PPIs (antacids) alter bacteria when overused.
•Sleep deprivation: Circadian rhythm disruption affects gut microbiome composition.
Q: How to support gut health — evidence-based actions.
Dietary fibre (most evidence): Feeds Bifidobacterium, Lactobacillus. Target 25-38g/day.
•Prebiotic foods: garlic, onions, leeks, asparagus, bananas, oats, legumes, chicory
Fermented foods (emerging evidence): Increase microbiome diversity.
•Curd/yoghurt (live cultures), buttermilk, idli/dosa (fermented), kanji (fermented rice water), kefir, kimchi
Diverse plant foods: Aim for 30+ different plants/week (colours, types). Each plant type feeds different bacteria.
Polyphenols: Plant compounds that selectively feed beneficial bacteria.
•Sources: berries, dark chocolate, green tea, olive oil, turmeric, spices
Exercise: Regular moderate exercise increases microbial diversity.
Sleep: 7-9 hours supports circadian rhythm and microbiome stability.
Q: Probiotics and prebiotics — what do they do?
Probiotics: Live microorganisms that, when consumed in adequate amounts, confer health benefit (WHO definition).
•Lactobacillus acidophilus, Bifidobacterium longum (common strains)
•Evidence: good for antibiotic-associated diarrhoea, IBS, traveller's diarrhoea
•Benefit is strain-specific — not all probiotics work for all conditions
•Food sources preferred over supplements for general gut health
Prebiotics: Food components (mainly fibres) that selectively feed beneficial gut bacteria.
•Inulin (chicory, garlic, onion), FOS (fructooligosaccharides), beta-glucan (oats), resistant starch
Synbiotics: Combination of probiotics + prebiotics (e.g., yoghurt with inulin).
Q: IBS (Irritable Bowel Syndrome) — understanding and management.
IBS: Functional gut disorder — no structural damage but significant symptoms.
Prevalence: ~10-15% globally. More common in women.
Symptoms: Abdominal pain, bloating, altered bowel habits (diarrhoea, constipation, or both), urgency.
Types: IBS-D (diarrhoea predominant), IBS-C (constipation), IBS-M (mixed).
Low-FODMAP diet (strongest evidence): Reduce fermentable carbohydrates that cause gas/bloating.
•Avoid: onions, garlic, wheat, dairy, apples, watermelon, legumes (high FODMAP)
•Allowed: rice, potatoes, carrots, strawberries, firm tofu, hard cheese
•3-phase: elimination → reintroduction → personalisation
•Works for ~75% of IBS patients.
Revision Notes
GUT MICROBIOME: trillions of microorganisms in large intestine
Functions: fibre digestion → SCFAs | vitamin synthesis | 70% immune cells | 90% serotonin
HARM:
Antibiotics (disrupts diversity) | Ultra-processed food | Chronic stress | Low fibre | Alcohol
SUPPORT:
Fibre (25-38g/day): prebiotics (garlic, onion, oats, legumes)
Fermented foods: curd, idli/dosa, buttermilk (probiotics)
30+ plant varieties/week | Polyphenols (berries, turmeric, green tea)
Exercise | Sleep (7-9hr)
PROBIOTICS: live microorganisms. Strain-specific effects.
Good evidence: antibiotic diarrhoea, IBS, traveller's diarrhoea
PREBIOTICS: fibre that feeds beneficial bacteria
IBS: functional disorder. Low-FODMAP diet most evidence-based.
Phases: eliminate high FODMAP → reintroduce → personalise (works for ~75%)
