Does Inulin (Chicory Root Fiber) Cause Gas?What Studies Show

Inulin is a plant fiber, often taken from chicory root or agave, that’s added to foods to raise their fiber count. It’s sold as a prebiotic, and in trials prebiotics raised levels of bifidobacteria, a group of gut bacteria.¹ Food makers can include it in the dietary fiber number on US nutrition labels.²

How much healthy adults tolerate

Chicory inulin. In a trial of 26 healthy adults, each person ate a breakfast with a placebo or with 5 or 10 grams of one of two inulin fibers: standard inulin, or a shorter-chain form called oligofructose.³

• Both fibers mildly increased symptoms; gas was most common, then bloating.³
• 10 grams of oligofructose caused substantially more symptoms.³
• Up to 10 g a day of standard inulin and 5 g of oligofructose were well tolerated.³

Agave inulin. In a US trial of 29 healthy adults, each took a placebo, 5 g or 7.5 g a day for 3 weeks at a time.⁴

Daily dose	Symptom score, out of 12
Placebo	0.44
5 g	1.94
7.5 g	2.34

Bloating, gas and rumbling rose slightly, and at 7.5 g people had more bowel movements and softer stools.⁴

In people with IBS

A review of 11 trials with 729 adults with IBS or similar bowel problems tested prebiotic fibers.¹

• Overall, they didn’t improve symptoms or quality of life compared with placebo.¹
• Inulin-type fibers made flatulence worse.¹
• Lower doses, 6 g a day or less, and other kinds of prebiotic eased flatulence a little.¹

Reading the label

Check ingredient lists for inulin, chicory, oligofructose or agave inulin. The trials measured grams per day, so several fiber-boosted products in one day add up.

Testing it on yourself

1. Note the timing. In the agave trial, breath hydrogen, a sign of fermentation, rose 5 to 8 hours after eating.⁴
2. Cut the added-fiber products for a week or two and see if gas eases, keeping the rest of your diet the same.
3. If you want the fiber, go back to one product at a time, at a lower dose.

See how much gas is normal, do beans make you gassy? and does a low FODMAP diet help IBS?

Try: “I started eating high-fiber bars for my gut and now I’m gassy and bloated every afternoon. Could the added inulin be the cause, and what’s a better way to get fiber?”

Bloated by Dinner covers fermentable carbohydrates in Chapter 9, “The Food Detective,” in a section called “The FODMAP Story.” Its Belly Clock logs what you ate and when your belly reacts, so a product’s effect shows up as a pattern. See the book.