Insoluble fibre is indigestible carbohydrate that does not dissolve in warm water.
Insoluble fibre is the type of fibre that adds bulk to our stools helping to pass solids out more easily.
Insoluble fibres found in our diet include cellulose, hemicellulose and lignins.
Insoluble fibre is important for maintaining good gut health. Good sources of this form of fibre are vegetables, fruit and whole grains.
Health benefits
Insoluble fibre is helpful for the health of our gut in the following ways:
- Promotes movement in the bowel
- Prevents constipation
- May help to reduce the risk of haemorrhoids (piles) and diverticulosis
- Helps good gut bacteria to grow
Which foods contain insoluble fibre?
Good sources of insoluble fibre include:
- Wholegrain foods such wheat bran, brown rice and couscous
- Root vegetables, such as carrots, parsnips and potatoes
- Celery, cucumbers and courgettes
- Fruit with edible seeds
- Beans, pulses and lentils
- Nuts and seeds
In terms of fruits and vegetables, the skins are a particularly good source of insoluble fibre.
Insoluble fibre, bowel movements and constipation
The bowel is a muscular organ that contracts to move contents through.
Insoluble fibre helps by adding bulk and moisture to stools which makes it easier for the bowel to steadily push its contents through and therefore helps to prevent constipation.
Because insoluble fibre helps to give stools moisture, it is important to drink the recommended intake of fluids, which in the UK is 6 to 8 cups, or around 1.2 litres, of non-alcoholic fluid.
Insoluble fibre, haemorrhoids and diverticulosis
Haemorrhoids, also known as piles, is a swelling of tissue in the rectum or anus which can be caused by persistent constipation.
Having to regularly strain to pass solids can put excess pressure on the blood vessels close to the anus, causing the area to become swelled.
Diverticulosis is when bulges form on the inside of the colon (large intestine) and cause bacteria to get trapped and can result in symptoms such as feeling sick, having a high temperature and rectal bleeding.
Having a diet with an adequate source of insoluble fibre can reduce problems associated with diverticular disease.
Insoluble fibre and gut bacteria
Our gut contains helpful bacteria which are essential for the health of our digestive system.
Helpful gut bacteria play a key role in helping to digest food for energy and promoting immune health.
- Gut inflammation: Blastocystis ST7 metabolism can trigger gut disease
- Microbiome: small changes in sleep patterns linked to harmful gut bacteria
- Weight gain triggered by toxic substances from gut
Gut bacteria feed off insoluble fibre and so this form of fibre is needed to help maintain a healthy level of helpful gut bacteria.
Insoluble fibre and blood glucose levels
People with diabetes will want to strike a balance between having food with a good source of insoluble fibre and keeping blood glucose levels stable.
Some good sources of insoluble fibre such as potatoes and whole grain foods are relatively high in carbohydrate so should be eaten in moderation, particularly if after meal blood glucose levels are consistently too high.
Generally speaking, non-starchy vegetables and fruits with lower carbohydrate content are a good way of getting insoluble as well as soluble fibre into your diet whilst not raising blood sugar levels too high.
Non-starchy vegetables are particularly good for people looking to lose weight.
