The Best-Researched Ingredients for Gut Health

Gut health formulas are crowded with ingredients, but the human evidence behind them varies enormously. Below we rank the ingredients that appear in the gut supplements we review, from strongest to weakest human evidence for digestive comfort and regularity. Doses are those used in studies, which are often far higher than what a capsule or gummy contains.

Strong evidence

1. Psyllium

What it is: a soluble, gel-forming fiber from the husk of Plantago ovata seeds and a standard bulk-forming laxative. What studies show: a 2022 meta-analysis of 16 randomized trials found fiber improved chronic constipation, with psyllium among the most effective types; a 2026 meta-analysis in IBS also found a clinical response with psyllium. Studied dose: about 10 to 12 g a day. Cautions: take with at least 8 ounces of fluid, expect some gas at first, and separate from certain medicines (MedlinePlus). Read more about psyllium.

Moderate evidence

2. Prunes

What it is: dried plums rich in fiber and sorbitol. What studies show: 80 to 120 g a day increased stool weight and frequency in a randomized trial, and 100 g a day improved bowel movements in adults with chronic constipation in a US trial. Studied dose: 80 to 120 g of whole prunes a day. Cautions: gas and natural sugars. Read more about prunes.

3. Bacillus coagulans

What it is: a spore-forming probiotic. What studies show: some strains ranked among the more effective probiotics for IBS pain and bloating in a 2023 network meta-analysis, and the Unique IS2 strain improved IBS symptoms in a randomized trial. Studied dose: varies by strain, often in the billions of CFU. Cautions: effects are strain-specific; mild gas early on. Read more about Bacillus coagulans.

4. Flaxseed

What it is: ground seeds of Linum usitatissimum, providing fiber, mucilage and ALA. What studies show: improved constipation symptoms at 10 g twice daily in a placebo-controlled trial and at 50 g a day in a trial against lactulose; a small IBS pilot was inconclusive. Studied dose: 10 to 50 g a day. Cautions: bloating at higher doses and theoretical blood-thinner interactions (NCCIH). Read more about flaxseed.

5. Chicory inulin

What it is: a prebiotic fiber. What studies show: a 2023 meta-analysis found chicory inulin-type fructans increase Bifidobacterium and can improve some measures of bowel function. Studied dose: gram-level daily amounts, far more than a gummy provides. Cautions: gas and bloating, especially at higher doses. Read more about inulin.

6. Oat bran

What it is: the outer layer of the oat grain, rich in beta-glucan. What studies show: 3 g or more of oat beta-glucan a day lowered LDL cholesterol in a meta-analysis of 28 trials; direct evidence for bowel regularity from oat bran supplements is limited. Studied dose: at least 3 g beta-glucan a day. Cautions: gas when increased quickly. Read more about oat bran.

7. Ginger

What it is: the root of Zingiber officinale. What studies show: NCCIH reports it may help pregnancy-related nausea, with less clear results for other uses; evidence for bloating or regularity is limited. Studied dose: varies by study; no standard digestive dose is established. Cautions: heartburn and stomach upset. Read more about ginger.

Limited evidence

8. Glucomannan

What it is: an absorbent fiber from konjac root. What studies show: 4.5 g a day increased bowel movements in very small studies, and a meta-analysis in children found more frequent bowel movements but no clear improvement in stool consistency. Studied dose: about 3 to 4.5 g a day. Cautions: must be taken with plenty of water; esophageal obstruction has been reported. Read more about glucomannan.

9. Apple pectin

What it is: a soluble fruit fiber. What studies show: 24 g a day shortened colonic transit time in one trial of adults with slow-transit constipation. Studied dose: 24 g a day. Cautions: gas at high doses. Read more about apple pectin.

10. Aloe vera

What it is: a succulent whose inner gel and latex are used differently. What studies show: a meta-analysis of three small trials found short-term improvement in IBS symptoms. Studied dose: varied gel or juice products. Cautions: latex and whole-leaf forms can cause cramps, low potassium and, rarely, liver injury; avoid in pregnancy (NCCIH). Read more about aloe vera.

11. Lactobacillus acidophilus

What it is: a common probiotic species. What studies show: the NCFM strain combined with a Bifidobacterium reduced bloating in a double-blind trial of people with functional bowel disorders. Studied dose: 200 billion CFU a day combined in that trial. Cautions: strain matters; products that do not name a strain cannot rely on this evidence. Read more about L. acidophilus.

Preliminary evidence

12. Bentonite clay

What it is: a volcanic clay. What studies show: a purified pharmaceutical montmorillonite eased abdominal discomfort in constipation-predominant IBS in a large trial but did not change stool frequency; there is no good evidence for supplement-grade clay as a “cleanse.” Studied dose: 3 g three times a day of the pharmaceutical form. Cautions: possible lead and arsenic contamination, and it may bind medicines. Read more about bentonite clay.

13. Black walnut hull

What it is: the hull of Juglans nigra, promoted for parasite cleanses. What studies show: only lab research on its compounds, such as juglone (2024 study). Studied dose: none established in humans. Cautions: avoid with tree nut allergy; not a substitute for medical treatment of parasites. Read more about black walnut.

The takeaway

The ingredients with the best evidence for digestive regularity are simple and inexpensive: psyllium, prunes and ground flaxseed, used at gram-level doses with plenty of water. Probiotics can help some people with IBS-type symptoms, but only specific, named strains. Clay and black walnut, the stars of many “cleanse” formulas, sit at the bottom of the evidence ladder. Before starting any of these, especially if you take medicines or have a digestive condition, talk to your doctor or pharmacist.