Food and the gut
What is fibre? Why your gut needs it every day
Fibre is the part of plant food that the small intestine cannot digest. It reaches the colon, where it holds water in the stool and feeds gut bacteria. People who eat more fibre have lower rates of heart disease, type 2 diabetes and bowel cancer. Most adults need 25 to 30 grams a day, from vegetables, fruit, pulses, whole grains and millets.
In short
- Fibre softens and bulks the stool, feeds gut bacteria, slows the absorption of sugar and helps you feel full.
- Large studies show the greatest benefit at 25 to 29 grams a day or more.
- Different fibres do different jobs, so variety matters.
- Increase fibre gradually over two to four weeks, with enough water, to avoid gas.
What are the types of fibre?
| Type | What it does | Where it is found |
|---|---|---|
| Soluble fibre | Forms a gel; softens stool, lowers cholesterol, slows sugar absorption | Oats, isabgol, pulses, apples, citrus fruit, carrots |
| Insoluble fibre | Adds bulk and speeds passage | Wheat bran, whole grains, vegetable skins, leafy greens |
| Fermentable (prebiotic) fibre | Feeds beneficial gut bacteria | Onion, garlic, banana, pulses, oats, cooked and cooled rice |
Most plant foods contain a mixture.
What does fibre do in the gut?
Keeps stools soft and regular
It holds water and adds bulk, so stool passes without straining. This protects against piles and fissures.
Feeds gut bacteria
Bacteria ferment fibre into short-chain fatty acids, the main fuel for the cells lining the colon.
Steadies blood sugar
Soluble fibre slows the absorption of sugar after a meal.
Lowers cholesterol
Soluble fibre binds bile acids, and the liver uses cholesterol to replace them.
Helps with weight
High-fibre meals are more filling for the same calories.
What does the evidence show?
A series of reviews covering many long-term studies and trials found that people with the highest fibre intake had a 15 to 30 percent lower risk of death from any cause, heart disease, stroke, type 2 diabetes and bowel cancer than those with the lowest intake. The benefit was greatest at 25 to 29 grams a day, with signs of further gain above that.
Which Indian foods are good sources?
- Pulses: all dals, rajma, chana, lobia, sprouts
- Whole grains and millets: whole-wheat atta, ragi, jowar, bajra, oats, brown or hand-pounded rice
- Vegetables: beans, carrot, okra, gourds, drumstick, leafy greens, cabbage, peas
- Fruit, with the skin where it is eaten: guava, apple, pear, orange, papaya, banana
- Nuts and seeds: peanuts, almonds, flaxseed, sesame, chia
- Isabgol (psyllium): a soluble fibre supplement, useful when food is not enough
Refined flour, polished rice, juices and packaged snacks contain little.
How do I increase fibre without gas?
Go slowly
Add one extra serving every few days over two to four weeks. Gut bacteria need time to adapt.
Drink more water
Fibre works by holding water. Without enough fluid it can worsen constipation.
Cook and soak
Soak pulses overnight and cook them well. Cooked vegetables are gentler than raw ones at first.
Spread it out
Include some fibre at each meal, not all at once.
When should I be careful with fibre?
- IBS: soluble fibre helps; coarse bran often worsens bloating. See IBS.
- A narrowed bowel, as in some people with Crohn’s disease: follow the advice of your doctor.
- Slow stomach emptying: large amounts of fibre can sit in the stomach.
- During an attack of diverticulitis: a low-fibre diet for a few days, then back to high fibre.
Questions patients ask me
Does fibre cause gas and bloating?
A sudden increase does, because bacteria ferment it. A gradual increase with enough water is usually well tolerated, and the gas settles within a few weeks.
Can I take isabgol every day?
Yes. It is a natural soluble fibre and is suitable for long-term use. Take it with a full glass of water, and keep it two hours apart from other medicines.
Is fruit juice as good as whole fruit?
No. Juicing removes most of the fibre and leaves the sugar. Eat the fruit whole.
Do I get enough fibre from roti and rice?
Whole-wheat roti provides some. Polished rice provides very little. The bulk of your fibre should come from the dal, vegetables and fruit eaten with them.
Sources
This page is written for patients and is based on the guidelines and studies below. It is for education and does not replace a consultation.
- Systematic reviews of carbohydrate quality and human health. Reynolds A et al. Lancet. 2019. PubMed 30638909
- International consensus statement on the definition of prebiotics. Gibson GR et al. Nat Rev Gastroenterol Hepatol. 2017. PubMed 28611480
- American College of Gastroenterology guideline on irritable bowel syndrome. Lacy BE et al. Am J Gastroenterol. 2021. doi:10.14309/ajg.0000000000001036
- Systematic review of fibre for haemorrhoid symptoms. Alonso-Coello P et al. Am J Gastroenterol. 2006. PubMed 16405552