Nutrition and diet

Dietary fibre

Also called: fibre, dietary fiber, roughage

Dietary fibre is the part of plants that humans cannot digest. Instead, it travels to the colon, where bacteria ferment it into short-chain fatty acids. The NHS recommends 30 grams a day for UK adults. The current average is around 19 grams. Higher fibre intake is linked to lower risk of bowel cancer, heart disease and type 2 diabetes.

The two types

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.

What 30 grams a day looks like

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 19 grams, mostly from wheat products with little plant variety.

Top fibre foods per UK portion

  • 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.

Why fibre matters beyond regularity

  • Lowers risk of bowel cancer. The strongest evidence comes from large UK and European cohort studies showing a roughly 25 percent risk reduction for the highest fibre intake compared with the lowest.
  • 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 stretch the gut and trigger satiety hormones, which can reduce overall calorie intake without conscious effort.

How to ramp up without bloating

Increase fibre slowly. Add about 5 grams a week 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.

Common questions

Can you have too much fibre?
Yes. Above 50 to 60 grams a day, most people experience bloating, gas and irregular stools. Excess fibre can also bind some minerals like iron and zinc, reducing absorption. The 30 grams a day NHS target sits well below problem levels.
Are fibre supplements as good as fibre from food?
Psyllium husk and partially-hydrolysed guar gum have the best evidence among supplements. They help where the diet falls short. Whole foods give you fibre alongside polyphenols, vitamins and minerals, so they remain the first choice.
Does fibre help or hurt if I have IBS?
It depends on type and dose. Soluble fibre, especially psyllium, helps both IBS-D and IBS-C. Insoluble fibre and high-FODMAP fibres often worsen IBS symptoms. The NICE-recommended approach is to start with low-dose soluble fibre and adjust by symptoms.
Why does fibre cause gas?
Bacteria in the colon ferment fibre and produce gas as a by-product. The gas is normal and the bacteria are doing helpful work. Most people adapt within 2 to 4 weeks of a higher-fibre intake. Slow ramp-up and adequate water reduce the discomfort.

Sources