Quick answer

Inulin is a plant fiber that people cannot digest, so bacteria in the large intestine ferment it. Trials using 3 to 20 g a day found more bifidobacteria, and 8 to 10 g a day raised calcium absorption. Effects on bowel habits were smaller and depended on chain length. Gas and bloating are the usual side effects.^1,2,3

Key facts

FDA lets inulin count as dietary fiber on US labels, and the Daily Value for all dietary fiber is 28 g a day.^4,5
Trials of chicory inulin-type fructans used 3 to 20 g a day, and bifidobacteria rose within 2 weeks at 5 to 8 g a day.^1,6
Chain length changes the result: short-chain fructans raised bowel movements in a 2019 meta-analysis, while long-chain inulin showed no clear change.⁷
Gas is the most common complaint and it grows with the amount. A 10 g serving of short-chain oligofructose was harder on the gut than 10 g of native inulin.^3,8
The levothyroxine label says dietary fiber may bind the medicine and lower how much is absorbed, and inulin counts as dietary fiber.^4,9

What inulin is

Inulin is a carbohydrate called a fructan: a chain of fructose units joined by bonds that human digestive enzymes cannot break. Plants such as chicory, Jerusalem artichoke, agave, onions and garlic make it as a way to store energy.^2,10

Human digestive enzymes cannot break the bonds in inulin, so it reaches the colon intact, where bacteria ferment it.²

Inulin is a soluble fiber, but unlike many soluble fibers it does not thicken into a viscous gel.²

FDA counts inulin and inulin-type fructans as dietary fiber on Nutrition and Supplement Facts labels, a decision it announced in June 2018 while it prepares a rule.^2,4

Ingredient lists may show inulin as inulin, chicory root, chicory root extract, chicory root fiber, chicory vegetable fiber, oligofructose or fructooligosaccharide.²

Inulin is a prebiotic, which means food for gut microbes, and not a probiotic, which means live microbes. The two are sometimes sold together. Our probiotics guide covers the live ones.^11,12

How it works in the gut

Inulin passes through the stomach and small intestine intact. In the large intestine, bacteria ferment it and make short-chain fatty acids and gas. That fermentation favors some groups of bacteria over others, bifidobacteria above all, which is why inulin is called a prebiotic.^2,11

Because inulin is not digested in the upper gut, it supplies fewer calories than digestible carbohydrates.¹³

The same fermentation explains both what people hope for and what they notice. A fiber that feeds bacteria also makes gas, which is why the side effects below grow with the amount.^2,3

What the evidence shows

Three benefits are graded here, all of them moderate. Most trials were small and short, and several had authors who worked for companies that make inulin or related fibers. Each basis below says so where it applies.^1,7,14

Increases bifidobacteria, a group of bacteria that live in the gut*^1,6,15,16,17

Moderate evidence

A 2023 meta-analysis of 50 randomized trials with 2,525 people aged 0 to 83 found that chicory inulin-type fructans at 3 to 20 g a day raised bifidobacteria. Smaller trials found the same at 5 g a day of chicory or Jerusalem artichoke inulin, and people who started with fewer bifidobacteria saw the larger rise. Most trials were small and short, the meta-analysis had two authors from an inulin maker, and in one 7 day test long-chain inulin did not raise bifidobacteria while shorter fructans did. A review of adult studies also noted that the shifts in bacteria were not matched by higher short-chain fatty acid levels.

Amount studied: 3 to 20 g a day; 5 g a day was enough in two trials

People who start with fewer bifidobacteria tend to see the larger rise, and in two dose studies more inulin did not reliably mean a bigger effect.^6,16

Helps the body absorb calcium from food*^2,18,19

Moderate evidence

FDA's 2018 science review found nine human studies of calcium absorption with inulin-type fructans that it could draw conclusions from, and six found more calcium absorbed. In the longest, 98 adolescents took 8 g a day of chicory inulin mixed with oligofructose or a placebo for a year: the inulin group absorbed about 8.5 percentage points more of its calcium at 8 weeks and 5.9 points more at one year, and gained more whole-body bone mineral. A 6 week crossover trial in 15 postmenopausal women at 10 g a day found more calcium and magnesium absorbed. Most studies were small, and oligofructose on its own did not raise absorption in one of them. FDA relied on this evidence to count inulin as dietary fiber.

Amount studied: 8 to 10 g a day of chicory inulin mixed with oligofructose, for 6 weeks to 1 year

Supports regular bowel movements at about 12 g a day, with a modest effect*^1,7,14,20

Moderate evidence

In 44 healthy adults with infrequent bowel movements, 4 g of chicory inulin three times a day for 4 weeks raised the median from 3 to 4 bowel movements a week and softened stools compared with placebo; two of the authors worked for the inulin's maker. A 2023 meta-analysis found better bowel function with chicory inulin-type fructans in healthy people. Results depend on the type: a 2019 meta-analysis found more frequent bowel movements with short-chain fructans but no clear change with long-chain inulin, and 20 g a day of chicory inulin did not change stool weight or transit time in 12 healthy men.

Amount studied: About 12 g a day of chicory inulin, as 4 g three times a day, for 4 weeks

Chain length may change the effect. A 2019 meta-analysis found more frequent bowel movements with short-chain fructans but not with long-chain inulin, and in a 7 day test, long-chain inulin did not raise bifidobacteria while short-chain fructans did.^7,16

Some trials looked at other outcomes this site does not cover, and the studies we read measured gut bacteria, calcium absorption and bowel habits. This guide makes no claim beyond those.^1,2

Types of inulin and what the names mean

Not every product sold as inulin is the same fiber. The main difference is how long the chains are, and chain length may change the effect.²¹

Native chicory inulin is a mix of chains from 2 to 60 fructose units long, averaging about 12.²¹

Oligofructose is the short-chain part of inulin, 2 to 8 units long with an average of 4. It tastes sweet and dissolves easily.^13,21

Long-chain inulin, sold as inulin HP, has chains of 10 to 60 units, averaging 25.²¹

Agave inulin comes from a different plant and has a different chemical structure from chicory inulin, and it has been studied far less.²²

Chicory is the source behind most of the trials we read. If a label does not say which plant the inulin comes from or how long its chains are, you cannot match it to a study.^1,22

How much people take

Trials of chicory inulin-type fructans used 3 to 20 g a day, and adult studies of inulin used 5 to 20 g a day.^1,17

There is no official recommended amount of inulin. Trials of bacteria used 5 to 8 g a day, calcium trials used 8 to 10 g a day, and one bowel trial used 12 g a day, so the amount that matters depends on what was measured.^2,6,14

The dosage guide puts these studies side by side. The timing guide covers when in the day trials gave it, and the how long guide covers how soon each result appeared.

Inulin in food

Inulin for supplements and food ingredients is extracted from plants such as chicory root, agave and Jerusalem artichoke, which most Americans rarely eat.²

Classic methods of measuring dietary fiber do not pick up inulin and oligofructose, so food tables often leave them out.²³

Wheat and onions supply most of the inulin Americans eat, and garlic, artichoke, shallots and leeks are richer per bite. The food guide has the numbers and the foods to know about if fructans bother you.^10,24

What's in ours

Our Apple Cider Vinegar capsules list 200 mg of inulin from Jerusalem artichoke root in a two-capsule serving. That is about 7 percent of the 3 g a day an expert panel gives as the usual minimum for a prebiotic effect, so we make no inulin claim for the product.¹¹

Side effects, medicines, and who should ask first

Gas is the most common complaint with inulin, followed by bloating. In healthy adults these were mild at 5 to 10 g, and they grew with larger amounts.^3,8,22

In people with irritable bowel syndrome and similar bowel disorders, a 2019 meta-analysis found that prebiotics did not ease symptoms overall and that inulin-type fructans made flatulence worse. Fructans can cause digestive symptoms in some people.^10,25

Allergic reactions to inulin are rare but have been reported, including anaphylaxis in a woman with artichoke allergy after she ate health foods with added inulin.²⁶

Ask your pharmacist or doctor first

The levothyroxine label says dietary fiber may bind levothyroxine and lower how much is absorbed. Inulin counts as dietary fiber on US labels, although the levothyroxine label does not name it.^4,9

On the medicine's label

We found no official upper limit for inulin. Trials in healthy adults used up to about 20 g a day for 2 to 4 weeks, and gas and other complaints rose with the amount.^8,20,27

Ask your doctor first if you take levothyroxine or another thyroid hormone⁹
Ask first if you have irritable bowel syndrome or another long-term bowel condition²⁵
Ask first if you are allergic to artichoke, because a reaction to inulin has been reported in someone with that allergy²⁶
Ask first if you are pregnant or nursing, or before giving inulin to a child

Questions people ask

What does inulin do for the body?

Gut bacteria ferment it. In trials it raised bifidobacteria at 3 to 20 g a day, raised calcium absorption at 8 to 10 g a day, and had a smaller, type-dependent effect on bowel habits.^1,2,7

Is inulin the same as fiber?

It is a kind of soluble fiber. FDA allows inulin and inulin-type fructans to be counted in the dietary fiber line of a label, although unlike many soluble fibers it does not thicken into a gel.^2,4

What is the best inulin to take?

There is no single best one. Chicory inulin is the best studied. Look for a label that names the plant, gives the grams in a serving and, ideally, says whether the chains are short or long, since results differ by chain length.^1,7

Does inulin do anything for skin?

This guide makes no claim about skin. The trials we read measured gut bacteria, calcium absorption and bowel habits.¹

Can inulin cause gas?

Yes. Gas was the most common complaint in trials, mild at 5 to 10 g in healthy adults and larger with bigger amounts. Short-chain oligofructose was harder on the gut than native inulin.^3,8

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.