Nutrition and diet

Inulin

Also called: fructans, chicory fibre

Inulin is a type of soluble fibre (a fructan) found in chicory root, onion, garlic, leek, asparagus, Jerusalem artichoke and bananas. It travels undigested to the colon, where it selectively feeds Bifidobacterium and other beneficial bacteria. It is one of the best-studied prebiotics, but it is also a FODMAP, so people with IBS often react to large doses.

What it does

  • Selectively feeds Bifidobacterium species.
  • Increases short-chain fatty acid (especially acetate) production.
  • Modestly improves bowel regularity.
  • Lowers post-meal glucose response.
  • Mildly lowers cholesterol at higher doses (over 10 g/day).
  • Increases mineral absorption (especially calcium and magnesium) in studies.

Food sources

  • Chicory root: fresh root contains roughly 11-20 g per 100 g; dried chicory and chicory-extract powders concentrate this up to ~40 g per 100 g (the figure often cited online refers to dried weight).
  • Jerusalem artichoke (16 g per 100 g).
  • Garlic (15 g per 100 g, raw).
  • Onion (4 g per 100 g, raw).
  • Leek (3 g per 100 g).
  • Asparagus (2 g per 100 g).
  • Bananas (0.5 g per banana, more in slightly green ones).
  • Wheat (0.5 g per slice of bread).

The FODMAP issue

Inulin is a fructan, classified as a FODMAP. For most people inulin is great. For people with IBS, especially IBS-D, it can produce serious bloating, gas and pain. The threshold varies, some IBS sufferers tolerate 2-3 g/day, others react to 0.5 g. If you have IBS, introduce inulin sources slowly or work through a structured low-FODMAP elimination first to find your tolerance.

Dose for healthy adults

  • From food: usual UK diet contains 1 to 4 g/day of inulin.
  • Beneficial dose for Bifidobacterium increase: 5 to 10 g/day, sustained for 2-4 weeks.
  • Supplement: start at 2 g/day, build up over 2 weeks.
  • Above 15 g/day: high gas and bloating likely even in tolerant people.
  • Powder form: cheap and easily added to drinks, smoothies, yoghurt.

Common questions

Is inulin safe in pregnancy?
Yes from food sources. Concentrated inulin supplements during pregnancy haven't been extensively studied, so most clinicians recommend food sources only.
Why does inulin make me so gassy?
Because it ferments rapidly. The very gas you experience is the same gas that signals bacterial activity. Most people adapt over 2 to 3 weeks. If you don't, you may have a FODMAP sensitivity worth investigating.
Is inulin the same as FOS?
Related. Inulin is a longer-chain fructan; FOS (fructo-oligosaccharide) is shorter-chain inulin. Both are fructans, both are FODMAPs, both feed bifidobacteria. Effects are similar.
Should I take an inulin supplement instead of eating onion?
Whole foods first. Onion, garlic and leek bring polyphenols and other compounds alongside the inulin. Concentrated supplements are useful if dietary intake is hard to maintain or you're targeting a specific microbiome shift.

Sources