L. reuteri and L. reuteri yogurt: what the trend promises and what the evidence shows

Short answer

L. reuteri (Lactobacillus reuteri) is a probiotic bacterium with a few well-studied strains, and most of its proven benefits are narrower than social media suggests. The strongest human evidence is for colic in breastfed babies: in a pooled analysis of four trials with 345 infants, the strain DSM 17938 cut crying and fussing by about 25 minutes a day after three weeks, with clear benefit in breastfed but not formula-fed infants (1). In one trial of 90 women aged 75–80, another strain slowed bone loss in the shin over a year (2).

L. reuteri yogurt is a home-fermented yogurt made from probiotic tablets, milk and fibre, left to ferment for about 36 hours (3). Claims about better skin, deeper sleep, higher oxytocin, libido and weight loss come mostly from mouse studies (4). No human trial has tested the homemade yogurt itself.

Is it safe? L. reuteri supplements are generally well tolerated in healthy people. Home fermentation for a day and a half at body temperature adds a food-safety risk if hygiene or temperature slip.

If you are trying L. reuteri because you feel bloated, tired or not like yourself, those feelings are real and not imagining things. They are worth taking seriously, with a doctor if they persist.

Note: this article is for general education and is not medical advice. L. reuteri is a dietary supplement, not a treatment for any disease. Do not give probiotics to a baby without talking to your paediatrician. If you are pregnant, have a weakened immune system, a central line, a serious illness or a bowel condition, talk to your doctor before taking probiotics or home-fermented foods. This guide is published by Welltory, which makes one of the apps mentioned. Welltory is a general wellness product: it helps you track and understand your data and does not diagnose or treat any condition.

What is L. reuteri?

Lactobacillus reuteri is a lactic-acid bacterium found naturally in the gut of humans and many animals, and in breast milk. In 2020, scientists split the huge Lactobacillus group into 25 genera based on genetics (5); L. reuteri's official name is now Limosilactobacillus reuteri, though products and articles still use the old name.

Strain matters more than species. Probiotic research is done on specific strains, and results for one strain do not automatically apply to another. Two L. reuteri strains dominate the research and the shelves:

• DSM 17938 — studied mainly for infant colic and gut symptoms.

• ATCC PTA 6475 — studied for bone density and in many of the animal studies behind the skin and oxytocin claims.

Both are sold under the BioGaia brand, and the tablets most often used for homemade L. reuteri yogurt contain both (3).

For an overview of probiotics in general, see our guides to probiotics and probiotics for gut health.

What are the benefits of L. reuteri, according to human trials?

Infant colic

In an individual participant data meta-analysis published in Pediatrics, researchers pooled four randomized trials with 345 infants with colic. Babies given L. reuteri DSM 17938 cried and fussed about 25 minutes less per day at day 21 than babies on placebo and were about 1.7 times as likely to have their crying halved. The benefit was clear in breastfed babies and not significant in formula-fed babies. The authors concluded it "can be recommended for breastfed infants with colic" (1). Several authors had industry ties.

Any decision about probiotics for a baby belongs with your paediatrician, who will also rule out other causes of crying.

Bone density in older women

In a 12-month trial in Sweden, 90 women aged 75–80 with low bone density took L. reuteri ATCC PTA 6475 (10 billion bacteria a day) or placebo. Bone density in the shin fell 0.83% with the probiotic and 1.85% with placebo; the difference of about 1 percentage point was just statistically significant (2). The study was funded in part by BioGaia, which supplied the product. One small trial is not enough to treat or prevent osteoporosis; it is a reason for more research. If bone health is your concern, our guide to menopause and bone loss covers the options with stronger evidence.

What is L. reuteri yogurt, and how is it made?

L. reuteri yogurt (sometimes called "super yogurt" or "SIBO yogurt") is a homemade fermented dairy product popularised by the US doctor and author William Davis. The usual method (3):

1. Crush about 10 BioGaia Gastrus tablets (containing DSM 17938 and ATCC PTA 6475).

2. Mix with prebiotic fibre — about 2 tablespoons of inulin or unmodified potato starch per quart (litre) of milk or half-and-half.

3. Ferment at around 96–100 °F (36–38 °C) for about 36 hours, much longer than ordinary yogurt.

4. Chill, and use part of the batch to start the next one, refreshing the starter every few batches.

The idea is that the long, warm fermentation multiplies the bacteria far beyond what a tablet contains. Nobody has published independent lab counts showing how many live L. reuteri a typical homemade batch contains, or that eating it reproduces the effects seen in studies.

Does L. reuteri yogurt work? Skin, sleep, oxytocin and weight

These claims are not supported by human trials. Most come from animal research, especially from one MIT group:

• Oxytocin and wound healing. In a 2013 study, giving L. reuteri to animals raised levels of the hormone oxytocin through the vagus nerve and made wounds heal in about half the time (4). Related studies in the same lab reported shinier fur and other effects in mice.

• Weight, libido, ageing skin. Similar mouse findings are behind these claims.

Mouse studies are a reasonable place to start research. They cannot tell you what a homemade yogurt will do for your skin, your sleep or your relationships. If you notice changes after starting it, remember that people who start a new ritual often change other habits at the same time, and expectations shape how we feel.

Is L. reuteri yogurt safe?

The bacteria themselves are generally well tolerated in healthy children and adults, and DSM 17938 has been given to babies in trials. The bigger questions are about the method and about who should avoid probiotics.

Home fermentation. Keeping milk at body temperature for 36 hours is exactly what harmful bacteria like too. Use clean equipment, a device that holds a steady temperature, and pasteurized milk. Throw a batch away if it smells off, shows mould, is pink, grey or slimy, or separates in an unusual way. When in doubt, don't eat it.

Who should talk to a doctor first:

• people with a weakened immune system (for example, on chemotherapy or after a transplant), a central venous line or a serious illness;

• people with short bowel syndrome or recent bowel surgery;

• pregnant people, because a long home fermentation is a food-safety question in pregnancy;

• parents considering it for babies or young children.

Side effects. Some people get gas or bloating for the first days. Large amounts of inulin in the starter can add to that.

How to choose an L. reuteri product

If you decide to try L. reuteri, a few checks make the difference between a product that matches the research and one that only borrows its name.

• Look for the strain code. A label that says only "L. reuteri" tells you the species, not the strain. The research behind colic and bone density used DSM 17938 and ATCC PTA 6475; a different strain may behave differently.

• Check the number of bacteria at expiry, not at manufacture. Live bacteria die over time. A reputable product states the CFU count guaranteed until the expiry date.

• Follow the storage instructions. Some products need refrigeration; heat in a car or a sunny kitchen can kill them.

• Prefer third-party testing. Supplements in the US are not checked by the FDA before sale, so independent testing is the only outside check on what is in the bottle.

• Start one product at a time. Many "gut health" blends combine several strains, fibres and herbs. If you feel better or worse, you won't know which ingredient did it.

L. reuteri yogurt vs regular yogurt vs capsules

For most people, a regular fermented food in the diet plus, if wanted, a capsule with a named strain is the simplest way to try L. reuteri without the food-safety worries of a long home fermentation.

How much L. reuteri do people take?

Supplements typically provide 100 million to 10 billion bacteria (CFU) a day, depending on the strain and the purpose. The colic trials used DSM 17938 drops given once a day for 21 days; the bone trial used 10 billion ATCC PTA 6475 a day for a year (1, 2). There is no established dose for adults' general health.

Supplements in the US are not approved by the FDA before sale. Look for a product that names the strain, not just the species.

How to check whether L. reuteri is doing anything for you

1. Name the goal. Bloating, bowel regularity, sleep or skin — pick one or two.

2. Record a baseline for two weeks: a 1–10 symptom score, sleep times, and anything else you want to follow.

3. Change one thing. If you start the yogurt, cut sugar and begin a new workout in the same week, you won't know what helped.

4. Give it four to eight weeks. Our guide on how long supplements take to work explains why.

5. Compare weekly averages and decide. If nothing changed, you have your answer.

Living with gut symptoms: the questions people ask next

Can L. reuteri yogurt help with SIBO?

There is no good evidence that it treats small intestinal bacterial overgrowth. SIBO is diagnosed with a breath test and usually treated with antibiotics and diet. Our guide to SIBO treatment covers the options; ask your doctor before adding a probiotic.

Is store-bought yogurt the same?

No. Regular yogurt is made with other bacteria, usually Streptococcus thermophilus and Lactobacillus bulgaricus, and some add other probiotic strains. It is a good food, but it does not contain the L. reuteri strains used in studies unless the label says so.

Can I make L. reuteri yogurt without dairy?

Some people ferment coconut milk or other plant milks with added fibre. Results are less predictable, and food-safety rules are the same.

Should men take L. reuteri for testosterone?

The testosterone claims come from mouse studies. No human trial shows that L. reuteri raises testosterone. If you have symptoms of low testosterone, a blood test is the way to find out; see our article on testosterone after 40.

Before you blame yourself

Gut symptoms, poor skin and low energy often get dismissed as stress or diet, and it is easy to feel you should fix them alone. They are worth a proper look. A probiotic can be an experiment; it should not replace a diagnosis when symptoms persist.

When to see a doctor

See a doctor if you have gut symptoms for more than a few weeks; diarrhea that won't settle; blood in your stool; unexplained weight loss; trouble swallowing; persistent abdominal pain; or a baby who cries inconsolably, feeds poorly or has a fever.

Seek urgent help for a high fever, signs of dehydration, severe abdominal pain, or a baby under three months with a fever.

How to bring this up with your doctor

What to ask for, by name. "Could my symptoms be IBS, coeliac disease, SIBO or something else, and what tests would you do?" and "Is a probiotic reasonable for me, and which strain?"

What to bring. Two to four weeks of symptom notes, a list of supplements with doses, and what you eat on a typical day.

What to say, out loud. "For [N] weeks I've had [bloating / loose stools / pain]. I've tried [yogurt / probiotics] and here's what changed."

If you're told it's just stress. Ask: "What would make you want to test further, and when should I come back?"

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How Welltory helps — and what it cannot do

The limits first. Welltory is a general wellness product, not a medical device. It does not measure your gut bacteria, hormones or oxytocin, and it cannot tell you whether a probiotic is working.

What it can do is help you keep a self-experiment honest by tracking the signals around it: sleep, stress and recovery.

Tag what you change. When Welltory detects a stress or recovery episode and asks "What happened?", you can tap a suggested tag, type, or answer by voice: "started reuteri yogurt", "bloated", "short night", "late dinner" (My Patterns).

Look at My Patterns after a few weeks. Patterns start to appear after around seven tagged events, and insight cards need at least seven occurrences of a tag in the current month plus some data from the previous month. They show which tags tend to come with stress and which with recovery; some sections, like the month-to-month comparison, need a paid plan (My Patterns).

Sleep, Battery and Stress. On iPhone with an Apple Watch or Oura, the Today screen shows Health, Battery and Stress: Battery starts each morning from your resting heart rate on waking and your sleep, and drops with stress through the day (Today screen). If you start the yogurt hoping to sleep better, this is where a change would show up.

HRV without a new device. You can take a spot HRV measurement with your phone camera and flash — a short, deliberate reading, not 24/7 tracking (camera measurements). Measure at the same time each morning (accurate HRV measurements).

A record for your doctor. From the web app you can export your data as CSV: Dashboard → choose a chart → pick the time range → Export (export guide). Patterns are associations to discuss with your doctor, not proof of what a supplement is doing.

For the full before-and-after method, see our guide on how to tell if a supplement or gadget is working.

How we made it

We based this article on an individual participant data meta-analysis of L. reuteri for infant colic, a randomized trial of L. reuteri in older women with low bone density, an animal study of L. reuteri, oxytocin and wound healing, the 2020 reclassification of the Lactobacillus genus, and a published home method for L. reuteri yogurt. Search questions came from what people in the United States most often ask about L. reuteri. For the product section, we checked every function against the Welltory Help Center on October 23, 2026.

Made with AI tools, then edited and fact-checked by the Welltory team. See our Editorial & AI policy.

Jane Smorodnikova, co-founder of Welltory, built the methodology behind how we read physiological data.

Written by Tatsiana Yashyna.

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