The answer
They do different jobs. ISAPP defines a fermented food by how it is made, with microbes, and many, like yogurt and kefir, carry live cultures when eaten; bread, most beers and heat-treated sauerkraut do not. A probiotic is a defined live strain given at a dose shown to benefit health. In a 10-week Stanford trial, adults eating about 6 servings of fermented food a day gained gut microbe diversity.
Key facts
- ISAPP defines fermented foods as "foods made through desired microbial growth and enzymatic conversions of food components."ISAPP consensus, 2021
- ISAPP defines probiotics as "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host."ISAPP; NIH ODS
- Sourdough bread and most commercial pickles are processed after fermenting and hold no live cultures when eaten.NIH ODS
- A US yogurt may claim "contains live and active cultures" only at 10 million CFU per gram at manufacture, with 1 million CFU per gram expected through its shelf life.21 CFR 131.200
- In Stanford's trial, fermented food intake rose from 0.4 to 6.3 servings a day, and 19 inflammatory proteins measured in blood fell.Wastyk et al., Cell, 2021
- Many probiotic supplements contain 1 to 10 billion CFU per dose.NIH ODS
What is the difference between fermented foods and probiotics?
A fermented food is defined by how it is made; a probiotic is defined by what it does. ISAPP's 2021 consensus panel says the two words cannot be swapped for each other.
The panel keeps the word probiotic for well-defined, characterized live microbes with a demonstrated health benefit, and that benefit has to come at least in part from the live microbes themselves, beyond the nutrition in the food. Most fermented foods do not meet that bar.
Some hold no live microbes by the time you eat them: ISAPP notes that bread is baked after fermenting, and most beers and wines go through steps that remove the microbes.
ISAPP keeps a third label, probiotic fermented food, for foods with a strain backed by strain-specific evidence, and expects most fermented foods sold today not to qualify.
Which fermented foods still have live cultures?
Many do, as long as they were not heated after fermenting. ISAPP's consensus sorts common foods by whether live microbes are present when you eat them, and NIH's Office of Dietary Supplements draws the same line.
| Food | Live cultures at purchase | What to look for on the label | Source |
|---|---|---|---|
| Yogurt | Yes, unless heat-treated after culturing | "Contains live and active cultures" is allowed at 10 million CFU per gram at manufacture, with 1 million CFU per gram expected through its shelf life; a heat-treated yogurt must say "does not contain live and active cultures" | 21 CFR 131.200; ISAPP |
| Kefir, sour cream, most cheeses | Yes | "Live and active cultures"; sold chilled | ISAPP; Harvard Health |
| Chilled sauerkraut and kimchi | Yes, when not heat-treated | "Naturally fermented"; in the refrigerated case | ISAPP; Harvard Health; Cleveland Clinic |
| Shelf-stable sauerkraut and pickles | Often not: heat-treated, or pickled in vinegar | Fermented, not just pickled | ISAPP; NIH ODS; Harvard Health; Cleveland Clinic |
| Miso, tempeh, natto | Yes, on ISAPP's list | No set wording | ISAPP |
| Kombucha | Most do; some are heat-treated | Chilled; bubbles alone are no proof, since some fizz is added carbon dioxide | ISAPP; Harvard Health |
| Sourdough and other bread | No: baked after fermenting | Nothing to look for | ISAPP; NIH ODS |
| Most beers, wine, soy sauce, vinegar | No | Nothing to look for | ISAPP |
Sources: ISAPP consensus (Box 1), NIH's Office of Dietary Supplements, 21 CFR 131.200 for the yogurt wording, and Harvard Health and Cleveland Clinic for the other label tips.
What the Codex food standard sets for kefir, and how much a day kefir trials gave, is in what is kefir?
Is yogurt a probiotic?
Not by default. Yogurt is a fermented food made with two named bacteria; in ISAPP's terms it is a probiotic food only if it also carries a strain with evidence of a health benefit.
The US standard for yogurt requires culturing with Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, and lets a maker heat it afterwards to extend shelf life, as long as the label then says it does not contain live and active cultures. NIH's Office of Dietary Supplements adds that yogurt may also contain probiotic microbes, such as Bifidobacterium, and that a food's probiotics should be listed on the label by genus, species and strain.
What did the Stanford fermented food study find?
More gut microbe diversity and fewer signs of inflammation in the fermented food group, measured against a high-fiber group. The trial was small, and its main measure did not change.
Wastyk and colleagues at Stanford (Cell, 2021) randomly assigned 36 healthy adults to a high-fermented-food diet or a high-fiber diet, 18 per group, for 10 weeks within a 17-week study. People in the fermented food group went from 0.4 servings a day to an average of 6.3 by the end, choosing their own foods from yogurt to kimchi.
What the study showed
Gut microbe diversity rose steadily in the fermented food group.
Wastyk et al., 2021
Levels of 19 inflammatory proteins measured in blood fell, and four types of immune cells showed less activation.
Stanford Medicine, 2021
In the high-fiber group, gut microbe diversity stayed stable over the same weeks.
Stanford Medicine, 2021
What it did not show
A change in the main outcome, a cytokine response score, in either group.
Wastyk et al., 2021
That the foods' own microbes moved in. Most of the new types of microbes did not come from the foods.
Wastyk et al., 2021
Comfort from the first week: bloating scores in the fermented group rose during the build-up, then the rise was no longer significant by the end.
Wastyk et al., 2021
Any result for people with a health condition. All 36 were healthy adults.
Wastyk et al., 2021
"the new taxa contributing to the increased diversity were largely not from the fermented foods themselves"
Wastyk et al., Cell, 2021. Taxa means types of microbes.
What does a probiotic supplement give you that food does not?
A defined strain at a stated count. A supplement is built around the microbes it names and prints how many there are; most fermented foods do neither.
| Question | Fermented food | Probiotic supplement |
|---|---|---|
| What defines it | How it is made: microbes ferment the food (ISAPP) | What it does: live microbes at a dose shown to benefit health (ISAPP) |
| Live microbes when eaten | Often, not always (ISAPP) | Yes: the definition requires live microorganisms (ISAPP) |
| Strains named | Rarely; most are undefined mixes (ISAPP) | Defined down to the strain (ISAPP) |
| How many microbes | Up to 100 billion lactic acid bacteria in a serving of many live-culture foods, at variable levels (ISAPP) | Many contain 1 to 10 billion CFU per dose; higher counts are not necessarily more effective (NIH ODS) |
| Evidence behind the word | None needed to say "fermented" (ISAPP) | A demonstrated health benefit (ISAPP) |
Sources: ISAPP's consensus statement (Table 1 and text) and NIH's Office of Dietary Supplements.
Whether a supplement strain does anything measurable for a healthy person is the subject of our research note, do probiotics work? Enzymes and probiotics are compared in digestive enzymes vs probiotics.
How do you add fermented foods without extra gas?
Slowly, and one or two at a time. Cleveland Clinic suggests starting small, and the Stanford group saw bloating rise during the build-up before it settled.
- Week one
Start small
Add one or two fermented foods to your meals at a time.
Cleveland Clinic
- Each shop
Shop the chilled case
Shelf-stable products labeled fermented are typically pickled in vinegar, not made with live organisms, and hold no probiotics.
Harvard Health
- Each shop
Read for live cultures
"Live and active cultures" on yogurt; "naturally fermented" on sauerkraut and pickles.
21 CFR 131.200; Harvard Health
- Each shop
Check salt and sugar
Some fermented foods carry high amounts of sodium or added sugar.
Cleveland Clinic
- Daily
Pair them with fiber
Beans, oats and oranges bring the soluble fiber gut bacteria use.
Cleveland Clinic
- Ongoing
Think in weeks
In the Stanford trial, diversity rose slowly and steadily across the 10 weeks, not in days.
Wastyk et al., 2021
More habits for the month are in our 30-day gut habits checklist; for bloating today, see what helps bloating fast, naturally. Bone broth often turns up on the same shopping lists; it is simmered, not fermented, and our read on bone broth and gut health sets out what it does contain. For grams of fiber per serving in beans, grains and fruit, see high-fiber foods for gut health. How quickly gut bacteria shift with any change in eating, and how quickly they drift back, is in how to reset your gut.
Where Physician's Choice fits
This site is published by Physician's Choice, a maker of gut health supplements, and it names no product. Fermented foods are groceries, and the label checks above work for any probiotic.
Notes on this page
- Where the question came from
- 1,031 public Reddit posts from 228 communities, Sep 5 to Oct 5, 2026. 63 were about probiotics, and 10 named fermented foods such as kefir, kimchi, sauerkraut or yogurt.
- What engines were asked
- Fermented foods for gut health, fermented foods vs probiotics, and whether yogurt is a probiotic.
- Products
- None. This site names no product, so no label is quoted.
- Sources
- 10 sources, each opened on Oct 9, 2026. The Stanford numbers come from the full paper and the university's own release.
- Checks
- Last checked Oct 12, 2026, when links to our research note on probiotics and our enzymes vs probiotics read were added. On Oct 16, 2026 a link to our yogurt read was added to the first short answer, on Oct 18, 2026 a link to our read on how to reset your gut, and on Oct 22, 2026 a link to our read on kefir. Each later check is dated here.
Short answers
Is yogurt a probiotic?
Not automatically. Yogurt is a fermented food made with two named bacteria, and ISAPP keeps the word probiotic for live microbes with a demonstrated health benefit. Check the cup: a US yogurt may say it contains live and active cultures, and one heat-treated after culturing must say it does not. Our yogurt read compares the types, from Greek to frozen.
How many servings of fermented food a day?
There is no official target. ISAPP notes that US dietary guidelines mention yogurt and kefir only under dairy, with no specific emphasis on fermented foods. In the Stanford trial, intake rose from 0.4 to 6.3 servings a day over 10 weeks, and bloating rose during the build-up.
Do fermented foods have more probiotics than supplements?
They are counted differently. ISAPP says a serving of many live-culture foods, such as yogurt or kefir, can hold up to 100 billion lactic acid bacteria, mostly unnamed and at variable levels. NIH says many probiotic supplements contain 1 to 10 billion CFU per dose, a count printed on the label.
Does jarred sauerkraut have live cultures?
Only if it was not heat-treated. ISAPP lists heat-treated or pasteurized fermented vegetables among foods without live microbes, and Harvard Health says shelf-stable products labeled fermented are typically pickled with vinegar. Look in the refrigerated case for sauerkraut labeled naturally fermented.
Which fermented foods did the Stanford study use?
Participants chose their own: yogurt, kefir, fermented cottage cheese, kombucha, vegetable brine drinks and fermented vegetables such as kimchi. Intake rose from 0.4 to an average of 6.3 servings a day over the study, and gut microbe diversity rose with it.
Sources
- Marco ML, Sanders ME, Hutkins R, et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol. 2021;18(3):196-208. pmc.ncbi.nlm.nih.gov/articles/PMC7925329
- ISAPP. Fermented foods, for consumers. isappscience.org
- NIH Office of Dietary Supplements. Probiotics, fact sheet for health professionals. ods.od.nih.gov
- NIH Office of Dietary Supplements. Probiotics, fact sheet for consumers. Updated November 17, 2025. ods.od.nih.gov
- Wastyk HC, Fragiadakis GK, Perelman D, et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021;184(16):4137-4153. pmc.ncbi.nlm.nih.gov/articles/PMC9020749
- Stanford Medicine. Fermented-food diet increases microbiome diversity, decreases inflammatory proteins, study finds. July 12, 2021. med.stanford.edu
- Code of Federal Regulations. 21 CFR 131.200, Yogurt. ecfr.gov
- Harvard Health Publishing. Do fermented foods live up to the hype? health.harvard.edu
- Harvard Health Publishing. Fermented foods for better gut health. health.harvard.edu
- Cleveland Clinic. 8 fermented foods for gut health. health.clevelandclinic.org