What is the difference between soluble and insoluble fibre?
The difference comes down to how each type behaves in water. Soluble fibre dissolves or swells in water and forms a gel-like texture, while insoluble fibre does not dissolve and helps give stools more bulk.
Both are forms of dietary fibre, the part of plant foods that is not fully digested or absorbed in the small intestine and reaches the large intestine. They play different roles in digestion, so the goal is not choosing one over the other. It is getting enough total fibre from a good mix of plant foods.
You might have heard fibre talked about as if it is one single nutrient. The reality is a little more nuanced, and that distinction helps explain why different foods can affect digestion differently.
| Fibre type | What it does in water | Main practical role | Common food sources |
|---|---|---|---|
| Soluble fibre | Dissolves or swells and forms a gel-like texture | Supports stool consistency and provides fermentable fibre for gut microbes | Oats, barley, legumes, apples, citrus, psyllium |
| Insoluble fibre | Does not dissolve | Adds bulk and supports regular bowel regularity | Wheat bran, wholegrain wheat foods, brown rice, nuts, seeds, vegetable skins |
Adults should consume 25–30g of total dietary fibre daily (men 30–38g, women 21–25g). There is no dietary reference intake for insoluble or soluble fibre, however experts recommend about 6-8g per day coming from soluble fibre.
How soluble and insoluble fibre work in the gut
Soluble fibre
Soluble fibre attracts water and can thicken stomach and intestinal contents into a softer, gel-like consistency. This is one reason it is often discussed in relation to digestion and stool form.
Some soluble fibres are fermented by gut microbes in the colon. In simple terms, they act as fuel for certain microbes, which is why soluble fibre often comes up in conversations about the gut microbiome and a healthy gut environment.
Not every soluble fibre behaves in exactly the same way. Solubility is a helpful label, but viscosity and fermentability matter too. For everyday eating, though, it is still a useful rule of thumb: soluble fibre is the type that mixes with water.
Insoluble fibre
Insoluble fibre does not dissolve in water. Its main practical role is adding bulk to intestinal contents and stool, which supports digestive movement and regularity.
It is generally less fermentable than many soluble fibres, although some parts can still be partly fermented. Even so, its big contribution is mechanical rather than gel-forming.
Because gut health content often focuses heavily on microbes, insoluble fibre can be easy to overlook. That would be a mistake. Bulk and movement matter too, especially in diets built around refined grains and convenience foods.
Which foods contain soluble fibre and insoluble fibre?
Many foods contain both types, so it is more accurate to think in terms of foods that are richer in one type rather than foods that are purely one or the other.
Foods richer in soluble fibre
- Oats and oat bran
- Barley
- Beans
- Lentils
- Chickpeas
- Split peas
- Apples
- Citrus fruits
- Psyllium husk
Oats are a good example of the overlap. They contain both soluble and insoluble fibre, but they are especially known for soluble beta-glucan.
Foods richer in insoluble fibre
- Wheat bran
- Wholegrain wheat breads and cereals
- Brown rice
- Nuts and seeds
- Leafy greens
- Cauliflower
- Green beans
- Potatoes with skin
- Vegetable stalks and skins
Keeping edible skins on fruit and vegetables is one of those small habits that can easily lift insoluble fibre intake.
Foods that give you a mix of both
Most whole plant foods provide a combination of soluble and insoluble fibre. Fruit, vegetables, legumes, oats, whole grains, nuts, and seeds all contribute.
A practical takeaway is to build variety across the day. A breakfast with oats and fruit, a lunch on wholegrain bread with salad and legumes, and a dinner with vegetables and brown rice will naturally cover more than one fibre type without needing to track categories too closely. For more ideas, see Best food for gut health.
Do you need both types of fibre?
Yes. For general digestive support, both types matter because they do different jobs.
Soluble fibre is associated with gel-forming and fermentable properties that help support a healthy gut environment. Insoluble fibre is more strongly linked with stool bulk and digestive movement. Since those roles are different, a varied intake makes more sense than trying to decide which fibre is “better”.
Many adults fall short because modern eating patterns tend to rely on refined grains and highly processed foods, while legumes, whole grains, fruit, vegetables, nuts, and seeds show up less often. If your meals are mostly white bread, low-fibre snacks, takeaway, or convenience foods, fibre intake can drop quickly.
Some common clues that your diet is low in fibre overall include:
- you rarely eat legumes, whole grains, fruit, vegetables, nuts, or seeds
- most of your grain foods are refined rather than wholegrain
- snacks are mostly low-fibre packaged foods
- bowel movements are infrequent or stools are often hard
Those signs are not diagnostic, but they are useful prompts to look at your overall eating pattern. You can also explore Top tips to maintain and improve your gut health and How to maintain a healthy digestive system and avoid digestive problems for broader digestive habits.
How can you increase fibre intake in a practical way?
The simplest approach is to add fibre to meals you already eat instead of trying to rebuild your diet from scratch. Small changes tend to stick better than dramatic overhauls.
- Choose oats instead of a low-fibre breakfast cereal.
- Add fruit to breakfast or snacks, keeping the skin on where edible.
- Swap white bread, pasta, or rice for wholegrain versions.
- Add beans, lentils, or chickpeas to soups, salads, pasta sauces, or grain bowls.
- Include nuts or seeds as part of snacks or breakfast.
- Keep vegetables easy to reach for, such as prepped salad leaves, carrots, or frozen veg.
It helps to spread fibre across the day rather than packing it into one meal. That mid-afternoon snack is often an easy place to add fruit, nuts, or roasted chickpeas.
Increase intake gradually over days to weeks, and make sure fluids come up with it. Adding fibre too quickly without enough fluid can lead to temporary bloating, gas, abdominal discomfort, or harder stools.
Should I take a fibre supplement?
Whole foods should stay the foundation because they provide fibre alongside vitamins, minerals, and other plant compounds. Still, a fibre supplement can be a useful convenience tool when meals are inconsistent or your intake tends to run low. Digest + Fibre or Clean Greens can fit into that kind of routine alongside a balanced diet.
Probiotic SB may be part of a broader routine for supporting gut health.
If you want to read more about the gut flora side of the picture, Top tips on maintaining healthy gut flora and What are good and bad gut bacteria go deeper.
Seek personalised healthcare advice before making major fibre changes if you have persistent digestive symptoms, ongoing bowel changes, recent bowel surgery, swallowing difficulties, or medically prescribed diet restrictions. If bowel discomfort is a recurring issue, How to deal with bowel discomfort covers that topic in more detail.
Frequently Asked Questions
Is soluble or insoluble fibre better for gut health?
Neither is universally better. Soluble fibre is often discussed for gut environment support and stool consistency, while insoluble fibre is more closely linked with stool bulk and regularity. For most people, getting both is the more practical goal.
Are fruits and vegetables a source of both types of fibre?
Yes. Most fruits and vegetables contain a mix of soluble and insoluble fibre. Skins, stalks, and tougher structural parts usually provide more insoluble fibre, while pectin-rich fruits such as apples and citrus are often highlighted for soluble fibre.
How do I know if I am not eating enough fibre?
A low intake of whole grains, legumes, fruit, vegetables, nuts, and seeds is a strong clue. Reliance on refined grain foods and highly processed snacks is another. Some people also notice infrequent bowel movements or hard stools, although these are not specific to fibre intake alone.
Should you increase fibre intake gradually?
Yes. Gradual increases are commonly recommended because they improve tolerance and reduce the chance of temporary bloating, gas, or abdominal discomfort. Pair the increase with adequate fluid intake.
References
- National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand including Recommended Dietary Intakes. Fibre. Available at: https://www.nrv.gov.au/nutrients/fibre
- National Institutes of Health, Office of Dietary Supplements. Dietary Fiber Fact Sheet for Health Professionals. Available at: https://ods.od.nih.gov/factsheets/DietaryFiber-HealthProfessional/
- Dahl WJ, Stewart ML. Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber. Journal of the Academy of Nutrition and Dietetics. 2015;115(11):1861-1870.
- Slavin J. Fiber and Prebiotics: Mechanisms and Health Benefits. Nutrients. 2013;5(4):1417-1435.
