Overview
The parts of plant food your own enzymes cannot break down. Soluble fibre forms a gel and feeds gut bacteria; insoluble fibre adds bulk and speeds transit. Most people in North America get around half the recommended amount.
Why your body needs it
Not digested by us — it feeds gut bacteria, adds bulk, slows glucose absorption and binds bile acids. Soluble and insoluble types do different jobs.
Food sources
- Legumes
- Whole grains and oats
- Fruit with skin
- Vegetables
- Nuts and seeds
Very high intakes can bind minerals such as iron and zinc.
Recommended intake
38 g (men) · 25 g (women) for most adults. The upper limit, past which harm becomes likely, is None established.
Reference intakes are population figures. Pregnancy, illness, age and medication all move an individual’s needs, which is one of several reasons this page is information rather than advice.
Low fibre / deficiency
Most at risk: Most people in North America — average intake is roughly half the recommendation.
Possible causes
A diet built on refined grains, meat and processed food, with few vegetables, legumes, fruit or wholegrains. Very common and rarely thought of as a deficiency.
Signs & symptoms
Constipation, and over time a less diverse gut microbiome. Low intake is associated with bowel disease and cardiovascular risk.
Every sign here has other, often likelier, explanations. A list of symptoms is a reason to look into something, never a diagnosis.
Testing / diagnosis
Not measurable in blood. Assessed by what you eat and how your bowels behave.
Food strategies
Legumes, wholegrains, vegetables, fruit with skins, nuts and seeds. Increase gradually over a couple of weeks and drink more water — a sudden jump causes bloating and can make constipation worse rather than better.
Supplements
Psyllium is the best-evidenced and works for both constipation and loose stools. Supplements do not carry the vitamins, minerals and polyphenols that fibre-rich food does, so they are a supplement rather than a substitute.
Safety
Rapid increases cause bloating, wind and discomfort. Increase gradually and with enough fluid.
Interactions: Can slow absorption of medicines — separate psyllium and similar from tablets.
When to seek professional advice
Speak to your doctor about a persistent change in bowel habit, blood in the stool, or unexplained weight loss. These are not fibre questions, and they need investigating.
This page is general reference information, not medical or dietetic advice, and it cannot account for your health history or medications. Decisions about testing, supplements or significant dietary change belong in a conversation with your doctor, pharmacist or a registered dietitian.