Fibre Supplements: Psyllium, Inulin, FOS — Which One Do You Need?

Why Most People Need More Fibre

UK average fibre intake is approximately 18–20g/day. The target is 30g/day. The shortfall has real consequences: constipation, reduced microbiome diversity, higher cardiovascular risk, and impaired glucose tolerance.

Food is always first. But fibre supplements can close the gap.

Types of Fibre: Soluble vs Insoluble

Soluble fibre dissolves in water, forming a gel. It: - Slows gastric emptying (increases satiety, reduces post-meal glucose spike) - Lowers LDL cholesterol (bile acids adsorbed by the gel are excreted rather than recycled) - Is fermented by gut bacteria to produce short-chain fatty acids (butyrate, propionate)

Insoluble fibre doesn't dissolve. It: - Adds bulk to stool - Speeds transit time (reduces constipation) - Does not significantly feed gut bacteria

Most whole plant foods contain both. Supplements tend to be predominantly one or the other.

Psyllium Husk

Type: Primarily soluble (70% soluble, 30% insoluble) Source: Seed husks of Plantago ovata

The most evidence-backed fibre supplement. Multiple RCTs show: - LDL cholesterol reduction: A 2018 meta-analysis of 28 trials found psyllium significantly reduces LDL cholesterol (average ~10mg/dL reduction) - Blood glucose management: Reduces post-meal glucose spikes and improves HbA1c in type 2 diabetes - IBS-C: First-line dietary intervention for constipation-predominant IBS — better than bran

Dose: 5–10g daily, taken with a large glass of water (essential — psyllium can cause obstruction if taken without adequate fluid).

Start low (1–2 teaspoons) and increase slowly — sudden high doses cause bloating in most people.

Inulin and FOS (Fructooligosaccharides)

Type: Soluble, prebiotic Source: Chicory root (inulin), sugar beet (FOS), various plants

These are prebiotics — not absorbed, but fermented by Bifidobacterium and Lactobacillus. The fermentation produces butyrate and other SCFAs.

Benefits: - Significantly increases Bifidobacterium counts - Improves calcium absorption (short-chain fructooligosaccharides enhance calcium uptake in the colon) - Modest effects on bowel regularity

Important caveat: Inulin and FOS are high-FODMAP. For people with IBS, they can dramatically worsen bloating and gas — particularly in the first few weeks. Start extremely low (1g/day) if you have IBS.

Dose: 5–10g/day for gut health. Build up over 3–4 weeks.

GOS (Galactooligosaccharides)

Type: Soluble, prebiotic Source: Derived from lactose

Similar to FOS but with different bacterial targeting. GOS specifically stimulates Bifidobacterium species. Used in infant formula to mimic the prebiotic effects of human breast milk.

For adults: Good evidence for increasing microbiome diversity. Available in some specialist products. Lower FODMAP concern than FOS for most people.

XOS (Xylooligosaccharides)

Type: Soluble, prebiotic Source: Corncobs, sugarcane

Emerging evidence — effective at very low doses (1–2g) compared to FOS/inulin. Specifically stimulates Bifidobacterium. Well-tolerated even in IBS in small studies. May be a better option than inulin/FOS for sensitive guts.

Methylcellulose and Calcium Polycarbophil

Type: Insoluble and soluble (synthetic)

Used primarily for constipation management. Non-fermentable — less bloating than fermentable fibres. No prebiotic benefit but useful when fermentation-related bloating is a problem.

Wheat Bran

Type: Primarily insoluble Source: Outer layer of wheat grain

Good for constipation and stool bulk. Does NOT have the cholesterol-lowering effects of psyllium. Can worsen IBS symptoms in some people. Contains phytates which can reduce mineral absorption when consumed in very large amounts.

Choosing the Right Supplement

| Goal | Best choice | |------|------------| | Lower LDL cholesterol | Psyllium | | Improve blood glucose | Psyllium, beta-glucan (oats) | | Constipation | Psyllium, methylcellulose | | Microbiome diversity | Inulin/FOS, GOS, XOS | | IBS-C (no FODMAP issues) | Psyllium | | IBS with FODMAP sensitivity | Methylcellulose or small-dose psyllium | | General gut health | Diverse whole plant foods first, then inulin or GOS |

Practical Tips

1. Always increase fibre slowly — regardless of type. 5g/week increase is a reasonable rate. 2. Drink more water — fibre absorbs water; without it, constipation can worsen. 3. Combine types — a mix of soluble and insoluble fibre from food is more effective than any single supplement. 4. Don't rely on supplements over food — a varied plant-based diet provides fibre types, polyphenols, and micronutrients that no supplement can replicate.

If you have IBD, a motility disorder, or significant gut symptoms, consult a registered dietitian before adding high-dose fibre supplements.