Dietary fibre

Fibre is split into soluble and insoluble. Most plant foods contain both, in varying ratios. The split matters because the two types do different jobs and the gut tolerates them differently.

Soluble fibre

Dissolves in water and forms a gel. Slows the absorption of sugar and cholesterol. Feeds gut bacteria. Helps both constipation and diarrhoea by regulating water content of stool. Good sources: oats, barley, beans, lentils, peas, apples, pears, citrus fruits, psyllium husk, chia seeds.

Insoluble fibre

Does not dissolve in water. Adds bulk to stool and speeds up movement through the gut. Best for relief of slow-transit constipation. Can worsen gas and bloating in some IBS patients. Good sources: wholemeal bread, brown rice, wholegrain pasta, the skins of fruit and vegetables, nuts, seeds, wheat bran.

Hitting 30 grams takes intention. A typical example day: porridge with berries (8g) for breakfast, a wholemeal sandwich with hummus and salad (10g) for lunch, a handful of nuts (3g) as a snack, and a stir-fry with brown rice and mixed vegetables (10g) for dinner. Most UK adults eat closer to 20 grams, mostly from wheat products with little plant variety.

• Cooked porridge oats, 200g: 5 to 6g fibre.
• Tinned baked beans, half a 415g tin: around 8g.
• Wholemeal bread, two slices: 5 to 6g.
• Pear, one medium: 5g.
• Lentils, cooked, 100g: 8g.
• Almonds, 30g handful: 4g.
• Chia seeds, 1 tablespoon: 5g.
• Broccoli, cooked, 80g portion: 2g.
• Apple with skin, one medium: 4g.

• Lowers risk of bowel cancer. Pooled cohort evidence shows roughly a 10 percent lower risk of colorectal cancer for each extra 10 grams of fibre a day, with cereal fibre showing the strongest link.
• Lowers cholesterol. Soluble fibre, especially oat beta-glucan and psyllium, reduces LDL cholesterol modestly.
• Supports stable blood sugar. Soluble fibre slows glucose absorption.
• Feeds the microbiome. Bacteria ferment fibre into butyrate and other short-chain fatty acids that fuel the colon and reduce inflammation.
• Supports satiety. High-fibre meals can increase fullness through stomach distension, fermentation and changes in gut hormones, though the effect on overall calorie intake is inconsistent across studies.

Increase fibre slowly. Add a few grams every few days and drink more water. Start with soluble fibre rather than insoluble: oats and pulses are easier on the gut than bran and raw vegetables. People with IBS may struggle with high-fibre diets and should follow a low-FODMAP elimination if symptoms worsen, then reintroduce systematically.