Microbiome research moves fast and overstates itself faster. Fibre and fermented foods have the most dependable human data; most single-strain and single-food claims do not.
Digestion, regularity, the gut microbiome and gut-barrier function.
42 foods, grouped by the strongest rating any of its claims in this area reaches. Ratings describe the research, not the food. How ratings are decided.
Consistent findings across multiple good-quality human studies.
Several human studies point the same way, with real caveats.
Milk fermented with kefir grains, a rubbery symbiotic matrix of bacteria and yeasts that is strained out and reused. The yeast…
Digestive comfort: Some trials report that kefir improves lactose digestion and reduces associated symptoms, similar to yogurt. The kefir-specific trial base is smaller than the yogurt one.
Actinidia deliciosa
A fuzzy-skinned berry from a woody vine, with green or golden flesh and small edible black seeds. It contains actinidin, a…
Bowel regularity: Research suggests two kiwifruit a day increase stool frequency and soften stool consistency in people with constipation, with several trials pointing the same way. Trials are small, unblinded by nature and often conducted in the same few research groups.
Triticum aestivum
The entire wheat kernel — bran, germ and endosperm — either milled into wholemeal flour or cooked whole as berries. The USDA…
Bowel regularity: Research consistently shows that wheat bran increases stool weight and shortens transit time, and the effect is among the most reproducible in fibre research. It is a laxation effect, not a remedy for the causes of constipation.
Linum usitatissimum
The seed of the flax plant, sold whole, ground or pressed for oil, and the densest common dietary source of plant lignans. The…
Bowel regularity: Several trials report increased stool frequency and softer stools with ground flaxseed, consistent with the general effect of viscous soluble fibre plus the insoluble fraction of the seed coat.
Zingiber officinale
The rhizome of Zingiber officinale, used fresh, dried and ground, or pickled. Fresh and dried ginger are not interchangeable in…
Digestive comfort: Some trials report reduced nausea after surgery and during chemotherapy, and reviews generally find a small favourable effect. Results are less consistent than in pregnancy, doses vary widely between trials, and much of the research uses standardised capsules rather than ginger as eaten.
Mentha × piperita
A natural hybrid of watermint and spearmint, grown for its high menthol content and used fresh, dried or as an essential oil. The…
Digestive comfort: Enteric-coated peppermint oil capsules have been tested in irritable bowel syndrome across a number of randomised trials, and meta-analyses report improvement in global symptoms and abdominal pain compared with placebo. The studied product is a standardised oil capsule taken as a medicine, delivering far more menthol than mint leaves or an infusion, and reviews note that trial quality is uneven.
Early human work, or mostly lab and animal research.
Asparagus officinalis
The young shoots of a perennial lily relative, harvested in spring. White asparagus is the same plant grown covered so the spears…
Gut microbiome: Research suggests the inulin-type fructans in asparagus act as substrate for colonic bacteria, consistent with the broader prebiotic fibre literature. Trials using asparagus itself are few.
Brassica oleracea var. capitata
A dense-headed Brassica oleracea cultivar, eaten raw, cooked or fermented. Red varieties carry anthocyanins that change colour…
Gut microbiome: Research suggests cabbage fibre and fructans may act as substrate for colonic bacteria. Most microbiome findings involving cabbage come from fermented preparations, where live cultures rather than the vegetable itself may be doing the work.
Carica papaya
A soft tropical fruit with orange or red flesh and black seeds, eaten ripe as fruit and green as a vegetable. Its latex contains…
Bowel regularity: A small number of trials of papaya preparations report improved stool frequency and less straining in people with constipation. The studies are few, small and often use fermented or concentrated forms rather than fresh fruit.
Rubus idaeus
A hollow aggregate fruit made up of many small drupelets, harvested from thorny Rubus canes. Fragile enough that most of the crop…
Gut microbiome: Research suggests raspberry ellagitannins and fibre may shift the composition of gut bacteria, and only some people carry the microbes needed to convert those ellagitannins into urolithins. What those shifts mean for health is not yet clear.
Shredded cabbage salted and left to ferment under its own brine, where lactic acid bacteria already on the leaves acidify it…
Gut microbiome: Some trials report changes in gut microbial composition with regular intake of fermented vegetables. Most of this work groups fermented foods together rather than testing sauerkraut alone, and effects are modest.
Malus domestica
A pome fruit grown in temperate regions worldwide, with thousands of cultivars differing in acid, sugar and polyphenol content.…
Bowel regularity: Apples supply pectin and sorbitol, both of which affect stool water and transit. Trials on apples specifically are few, though the wider fibre literature supports the direction of the effect.
Musa acuminata
The fruit of a large tropical herb, harvested green and ripened after picking. Ripening converts most of its starch into sugars,…
Gut microbiome: Research suggests the resistant starch and fructans in less-ripe bananas may act as substrate for gut bacteria and increase short-chain fatty acid production. Human trials are small and the health consequences of those shifts remain unclear.
Piper nigrum
The dried unripe fruit of the Piper nigrum vine, used whole or ground. The USDA entry is per 100 g of ground pepper, whereas a…
Digestive comfort: Black pepper has a long culinary and traditional use as an appetite stimulant, and small human studies report changes in gastric secretion and transit. Research using symptom outcomes rather than laboratory measures is very sparse.
Fagopyrum esculentum
A pseudocereal seed from a plant in the rhubarb family, unrelated to wheat and free of gluten. The USDA reference entry is for…
Digestive comfort: Has been studied as a gluten-free grain alternative in coeliac disease, where the value lies in replacing wheat rather than in any property of buckwheat itself.
Coriandrum sativum
The dried fruit of Coriandrum sativum, the same plant whose leaves are sold as cilantro, though the seed tastes citrusy and warm…
Digestive comfort: Coriander appears as one ingredient in multi-herb preparations trialled for irritable bowel syndrome and functional dyspepsia, some of which report symptom improvement. Because it is almost never tested alone, its own contribution cannot be separated out.
Cuminum cyminum
The dried seed of Cuminum cyminum, used whole or ground across South Asian, Middle Eastern and Latin American cooking. The USDA…
Digestive comfort: Cumin has a traditional use for bloating, and a small number of trials of cumin oil in irritable bowel syndrome report symptom improvement. The evidence base is very small and uses concentrated oil rather than the seed.
Yogurt strained to remove much of its whey, roughly doubling the protein per spoonful and leaving a thicker set. Products…
Gut microbiome: Some trials report shifts in gut bacterial composition with regular yogurt intake. Changes are generally modest, transient, and vary a great deal between people and between products.
Salted napa cabbage layered with chilli, garlic, ginger and usually a seafood element, then fermented by the bacteria native to…
Gut microbiome: Some trials report shifts in gut microbial composition with regular kimchi intake. The studies are small, mostly conducted in one population, and the changes are modest.
Mangifera indica
A tropical stone fruit in the cashew family, with hundreds of cultivars differing sharply in fibre, sweetness and aroma. Eaten…
Bowel regularity: A small number of trials report improved stool frequency and consistency with daily mango in people with mild constipation. The studies are few and small, so this sits well short of established.
Allium cepa
The bulb of a cultivated Allium, used as a base flavour in most of the world cuisines. Cutting the bulb releases enzymes that…
Gut microbiome: Research suggests onion fructans act as a substrate for bifidobacteria and other colonic species, in line with the wider prebiotic literature on inulin-type fibres. Trials using onion rather than isolated inulin are scarce.
Lentinula edodes
A cultivated wood-decay fungus native to East Asia, sold fresh and dried. Drying concentrates its flavour compounds and is how…
Gut microbiome: Research suggests fungal beta-glucans and chitin reach the colon largely intact and are fermented there. Human data on shiitake specifically is early and the consequences of the microbial shifts are unclear.
Sorghum bicolor
A drought-tolerant cereal eaten whole, milled into flour or popped, and free of gluten. The USDA reference entry is for the dry…
Digestive comfort: Has been studied as a gluten-free cereal for people with coeliac disease, where the benefit comes from replacing wheat rather than from a property of sorghum itself.
Not enough human research to say anything useful yet.
Phaseolus vulgaris
A common bean variety whose dark seed coat carries anthocyanin pigments, staple across Latin America and the Caribbean. The USDA…
Gut microbiome: Several trials report increased short-chain fatty acid production and shifts in bacterial composition with regular bean intake, driven by resistant starch and oligosaccharides reaching the colon.
Animal bones and connective tissue simmered for many hours, which hydrolyses collagen into gelatin and gives the cooled liquid…
Digestive comfort: Evidence is limited for bone broth affecting gut symptoms or gut barrier function. Claims about repairing the gut lining rest on laboratory work with isolated amino acids such as glutamine, not on human trials of broth.
Elettaria cardamomum
The dried seed pods of Elettaria cardamomum, used whole or as ground seed in baking, curries and coffee. The USDA entry is per…
Digestive comfort: Cardamom is a traditional remedy for indigestion and is chewed as a breath freshener. Controlled human research on digestive symptoms is essentially absent.
Matricaria chamomilla
An infusion of dried Matricaria chamomilla flower heads, containing no caffeine and no tea leaf. Most clinical research on…
Digestive comfort: Chamomile is a traditional remedy for indigestion, colic and cramping, and appears in multi-herb digestive preparations. Trials of chamomile alone with digestive symptom endpoints are too few to support a conclusion.
Salvia hispanica
Tiny seeds from a Mexican member of the mint family that form a thick gel when hydrated, because of soluble mucilage in the seed…
Bowel regularity: Evidence is limited. The high viscous fibre content gives a plausible route to softer, more frequent stools, but trials measuring bowel outcomes for chia specifically are few.
Cicer arietinum
A pulse eaten whole, ground into gram flour, or blended into hummus, with the large kabuli and small desi types differing in seed…
Gut microbiome: Evidence is limited. A few trials report increases in bacteria that ferment resistant starch and oligosaccharides after regular chickpea intake, without established downstream health outcomes.
Phoenix dactylifera
The dried fruit of the date palm, around two-thirds to three-quarters sugar by weight, and used both as a fruit and as a…
Bowel regularity: Small trials report improvements in stool frequency and consistency when a daily portion of dates is added to the diet, consistent with their fibre content. The trials are few, small and short, and the same effect would be expected from other fibre sources.
Anethum graveolens
The feathery leaf of Anethum graveolens, used fresh with fish, cucumber and cultured dairy; the seed is a separate spice with a…
Digestive comfort: Dill and dill-containing gripe waters have a long folk use for wind and infant colic. The controlled trials are few, small and of low quality, usually testing multi-herb mixtures, so nothing can be attributed to dill itself.
Soybeans fermented with Aspergillus oryzae koji, salt and usually a grain, for anywhere from weeks to years. Longer ferments…
Gut microbiome: Evidence is limited for miso affecting the gut microbiome. Human trials measuring microbial outcomes after miso intake are essentially absent, and most miso is heated before it is eaten.
Whole soybeans fermented with Bacillus subtilis var. natto, which produces the sticky polyglutamic acid strands and pungent aroma…
Gut microbiome: Some trials report changes in gut bacterial composition with Bacillus subtilis intake. The organism is a spore former that survives stomach acid well, but human data using natto as the food is limited.
Myristica fragrans
The seed kernel of Myristica fragrans; mace is the lacy red aril around the same seed. The USDA entry is per 100 g of ground…
Digestive comfort: Nutmeg is traditionally used for diarrhoea and indigestion. Controlled human research on digestive symptoms is essentially absent, so nothing can be concluded.
Origanum vulgare
The dried leaf of Origanum vulgare, dominated by the phenols carvacrol and thymol. The USDA entry is per 100 g of dried leaf,…
Gut microbiome: Oregano oil is heavily promoted for small intestinal bacterial overgrowth and intestinal candida. Controlled human evidence for either use is absent, and self-treating suspected gut infections delays actual diagnosis.
Prunus persica
A summer stone fruit of the Rosaceae family, with fuzzy skin and a single hard pit. Nectarines are the same species differing by…
Bowel regularity: Peaches contribute fibre and sorbitol, both of which have a plausible laxative action, and stone fruits generally are used this way. Trials of peaches specifically are essentially absent.
Mentha × piperita
An infusion of dried or fresh peppermint leaf, containing no caffeine and no tea leaf. USDA does not publish a…
Digestive comfort: Peppermint tea is widely drunk for indigestion and wind, but almost all of the clinical research uses enteric-coated peppermint oil capsules in irritable bowel syndrome, which deliver far more menthol and deliver it further down the gut. Direct evidence for the infusion itself is thin.
Ananas comosus
A tropical bromeliad whose edible fruit is formed from many fused berries around a fibrous core. Notable for bromelain, a group…
Digestive comfort: Pineapple is widely described as a digestive aid on the strength of its enzyme content. There is no dependable human research showing that eating it improves digestion or reduces bloating in people with normal pancreatic function.
Secale cereale
A cold-hardy cereal grain used mainly for dense breads and crispbreads in northern and eastern Europe. The USDA reference entry…
Bowel regularity: Several trials report increased stool frequency and softer stools with wholegrain rye compared with refined bread, particularly in people who are constipated.
Whole cooked soybeans bound into a firm cake by Rhizopus mould, an Indonesian ferment that keeps the beans intact rather than…
Gut microbiome: Evidence is limited for tempeh affecting the gut microbiome. It is usually cooked before eating, which removes the live culture, and human trials measuring microbial outcomes with tempeh are essentially absent.
Oryza sativa
Rice milled to remove the bran and germ, leaving the starchy endosperm. The USDA reference entry is for raw grain; boiling…
Digestive comfort: Has been studied as a low-residue, low-FODMAP starch used when other grains are poorly tolerated. The tolerability rationale is widely accepted clinically but rests on limited trial evidence.