How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Prebiotics (inulin, FOS)
Dietary fibers (inulin, FOS) that nourish gut bifidobacteria: slightly more regular transit, a small drop in blood sugar in diabetics; nothing in irritable bowel syndrome, and extra gas.
Benefits
- Boosts gut bifidobacteria: clear effect in a meta-analysis of 50 studies (2,525 participants) with 3 to 20 g per day of chicory inulin; from 5 g per day in two weeks in 30 healthy adults
- Improves transit in case of constipation: more frequent, softer stools and faster transit in a meta-analysis of 5 trials (252 people)
- In prediabetics and type 2 diabetics, lowers fasting blood sugar by 0.60 mmol/l and HbA1c by 0.58 points (meta-analysis of 33 trials, 1,346 participants)
- Lowers triglycerides by 7.5% (0.17 mmol/l) in a meta-analysis of 15 trials
- In 150 obese people on a diet, 16 g of inulin per day for 3 months resulted in more weight loss than placebo, with a drop in diastolic blood pressure and insulin
- After Clostridium difficile diarrhea, fewer relapses with oligofructose than with placebo, in addition to antibiotics (142 patients)
- Increases the feeling of satiety in healthy adults and reduces sugar and insulin after the meal (review of 26 trials, 831 participants)
Precautions
Gas and bloating: in irritable bowel syndrome, inulin and FOS worsened flatulence, whereas other prebiotics at 6 g per day or less slightly reduced it; in constipation, inulin improved neither pain nor bloating. If you take metformin, the Food4Gut trial suggests that inulin will bring you little. The limits: in the 2021 meta-analysis (33 trials), the effects on blood sugar and blood fats are only observed in diabetics, and weight does not budge; the 2014 review judges the effects on weight, lipids, and inflammation to be contradictory; in irritable bowel syndrome, no trial is at low risk of bias; and more bifidobacteria is not a benefit in itself: in the Food4Gut trial, their increase is the "signature" of inulin rather than the cause of its effects.
Recommended dosage
5 to 20 g per day of inulin or FOS depending on the trials; 10 g per day for at least 6 weeks for blood sugar
How to take it
- Dose: 5 to 8 g per day were enough to increase bifidobacteria in two weeks; trials on metabolism use 10 to 20 g per day.
- Blood sugar: the meta-analysis of 33 trials retains 10 g per day for 6 weeks or more, in prediabetics or type 2 diabetics.
- Transit: short-chain fructans (FOS, oligofructose) increase stool frequency; long-chain ones showed no effect.
- Your diet matters: in 34 adults, 16 g per day changed the microbiota more in those who were already eating a lot of fiber.
- Metformin: in obese people, this treatment canceled most of inulin's effects on the microbiota and metabolism.
- What does not work: irritable bowel syndrome (11 trials, 729 patients: no better than placebo on symptoms and quality of life), weight outside of diabetes and a diet, and appetite in most trials in adults.
Did you know?
The more fiber you already eat, the more inulin changes your microbiota: in 34 adults, 16 g per day increased bifidobacteria in everyone, but only heavy fiber eaters saw other families of bacteria move, like Faecalibacterium.
What the studies say
This systematic review and meta-analysis studied the effects of chicory-derived inulin-type fructans on Bifidobacterium abundance and bowel function. Daily supplementation of 3 to 20 g of these fructans significantly increased Bifidobacterium in participants of all ages. Significant bifidogenic effects were observed in healthy individuals and those with health problems (except gastrointestinal disorders), with beneficial effects on bowel function in healthy people.
Nagy DU, Sándor-Bajusz KA, Bódy B, Decsi T, Van Harsselaar J, Theis S, Lohner S. — Critical reviews in food science and nutrition (2023) — View the source study
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more