What Is L Reuteri?
If you’ve been researching gut health, probiotics, or Dr. William Davis’s work, you’ve likely come across L reuteri — and for good reason. This remarkable probiotic bacteria has one of the most impressive bodies of research behind it of any single microbial strain, with benefits that go far beyond basic digestive support.
This is your complete guide to L reuteri — what it is, what it does for your health, how to get it, how to make L reuteri yogurt at home using the Dr Davis method, what to expect when you start, and how long it takes to work.
What Is L Reuteri?
Lactobacillus reuteri — commonly called L reuteri — is a probiotic bacteria that naturally lives in the human gut, skin, and mouth. It has been present in mammals for millions of years and was once a regular part of the human microbiome.
The problem is that modern life has largely wiped it out. Changes in diet, overuse of antibiotics, processed food consumption, and environmental toxins mean that the vast majority of people today have little to none of this bacteria in their systems. Research suggests that up to 97% of the population may be completely deficient in L reuteri — a dramatic shift from what previous generations carried naturally.
Dr. William Davis, cardiologist and bestselling author of Wheat Belly and Super Gut, has been one of the most prominent voices on L reuteri research. He has studied its wide-ranging health effects extensively and developed the homemade yogurt protocol that has become the gold standard for restoring L reuteri populations effectively.
L Reuteri Benefits
L reuteri has one of the broadest benefit profiles of any probiotic strain studied. Here is what Dr. Davis and the clinical research shows:
Gut Health
L reuteri helps maintain a healthy balance of gut bacteria, reducing populations of harmful microbes while supporting beneficial ones. Studies show it reduces symptoms of irritable bowel syndrome, bloating, and digestive discomfort by producing antimicrobial substances that suppress pathogenic bacteria. A healthy gut microbiome is fundamental to overall health — approximately 70% of the immune system lives in the gut.
Immune Function
L reuteri enhances the body’s natural defenses against infection and lowers systemic inflammation, helping the immune system respond more efficiently. This connects directly to glutathione — the body’s master antioxidant — which regulates immune responses and protects immune cells from oxidative damage. A gut that is functioning optimally produces less chronic inflammation, which reduces the burden on your glutathione reserves. Read more about this connection in our complete glutathione guide.
Skin Health
By reducing systemic inflammation, L reuteri can help address inflammatory skin conditions including acne and eczema. The gut-skin axis — the direct relationship between gut microbiome health and skin appearance — is one of the most active areas of research in dermatology, and L reuteri’s anti-inflammatory effects benefit skin from the inside out. Many users report clearer, healthier skin within weeks of consistent use.
L Reuteri Benefits for Women
For women specifically, L reuteri has shown benefits for hormonal balance, vaginal health, and skin. It helps restore healthy microbial balance in the vaginal microbiome, reducing the frequency of bacterial vaginosis and yeast infections. Its oxytocin-boosting effects also support mood stability and emotional wellbeing — particularly relevant during hormonal fluctuations.
L Reuteri Benefits for Men
For men, the research is equally compelling. Dr. Davis’s studies found that L reuteri supplementation in male subjects was associated with increased testosterone levels, improved muscle mass retention, and greater physical vitality. The metabolic benefits — improved insulin sensitivity and reduced abdominal fat — are also particularly relevant for men’s long-term health.
Mood and Mental Clarity
One of the most surprising findings in L reuteri research is its effect on mood. L reuteri stimulates production of oxytocin — the hormone associated with emotional connection, trust, and relaxation — and helps regulate cortisol, the primary stress hormone. Research by Dr. Davis found measurable improvements in mood, reduced anxiety, and a greater sense of social connection in subjects supplementing with L reuteri. The gut produces approximately 90% of the body’s serotonin, making gut health directly relevant to mental wellbeing.
Sleep Quality
L reuteri supports deeper, more restful sleep by influencing the production of sleep-regulating neurochemicals through the gut-brain axis. Users consistently report improved sleep quality — falling asleep more easily and waking more rested — as one of the earliest benefits they notice.
Heart Health and Blood Pressure
L reuteri has demonstrated meaningful cardiovascular benefits in clinical research. Studies show it can lower LDL cholesterol while improving HDL cholesterol, and may reduce blood pressure by lowering inflammation in blood vessel walls. For anyone with cardiovascular concerns, the anti-inflammatory effects of restoring healthy gut bacteria are worth understanding.
Weight Management
L reuteri can help curb appetite and promote a feeling of fullness, supporting weight loss efforts. It also reduces fat storage by improving metabolic function and insulin sensitivity — addressing one of the root causes of weight gain at the hormonal level rather than simply suppressing appetite.
Bone Density
Research shows L reuteri stimulates bone-building activity, making it beneficial for preventing or managing osteoporosis. This benefit is particularly relevant for postmenopausal women and older adults whose bone density naturally declines with age.
Athletic Performance and Recovery
L reuteri helps reduce muscle soreness and speeds up recovery after workouts. Athletes who supplement consistently report faster bounce-back between training sessions and reduced delayed onset muscle soreness — likely a result of its anti-inflammatory effects at the systemic level.
Dental Health
L reuteri reduces the population of harmful bacteria in the mouth, helping prevent cavities, reduce gum inflammation, and support overall oral health. Given that oral bacteria are a significant driver of systemic inflammation, this is another pathway through which L reuteri supports whole-body health.
Longevity
By reducing chronic inflammation and improving metabolic health across multiple systems simultaneously, L reuteri supports healthy aging at a fundamental level. Chronic low-grade inflammation is one of the primary drivers of age-related disease, and addressing it through microbiome restoration is one of the most evidence-based approaches available.
How to Get L Reuteri
Probiotic Supplements
Look specifically for products containing the strains DSM 17938 and ATCC PTA 6475 — these are the best-studied strains recommended by Dr. Davis. Not all L reuteri supplements contain these specific strains, so check the label carefully.
Fermented Foods
Some fermented foods like certain yogurts and kefirs may contain L reuteri, though concentrations are typically too low to produce significant effects. Making your own yogurt is far more effective.
Homemade L Reuteri Yogurt — The Best Option
The most effective way to restore L reuteri is making your own yogurt at home using the Dr Davis method. The extended fermentation process concentrates the bacteria to levels far higher than any commercial supplement or food product, making it the most potent and cost-effective approach available.
How to Make L Reuteri Yogurt — The Dr Davis Method
Ingredients
- 10 tablets or capsules of an L reuteri probiotic supplement containing strains DSM 17938 and/or ATCC PTA 6475
- 1 quart (4 cups) of organic half and half milk — whole milk or half-and-half gives the creamiest result; avoid ultra-pasteurized milk
- 2 tablespoons of prebiotic fiber such as inulin or raw potato starch — this feeds the bacteria and helps them grow
Equipment
- A 36 hour yogurt maker, Instant Pot, or any appliance that can maintain a constant temperature of 100°F (38°C) for an extended period
- A clean glass or ceramic container
- A thermometer (optional but helpful)
Instructions
Step 1 — Prepare the milk If using raw milk, heat to 180°F (82°C) to eliminate unwanted bacteria, then let it cool to 100°F (38°C). Standard pasteurized milk does not need heating — just warm it to 100°F.
Step 2 — Prepare the starter Crush the tablets into a fine powder using a mortar and pestle, or simply open the capsules. Combine with a small amount of the warmed milk to create a smooth slurry before adding to the full batch.
Step 3 — Add the prebiotic fiber Stir in 2 tablespoons of inulin or raw potato starch. Mix thoroughly to dissolve completely.
Step 4 — Combine and pour Add the probiotic slurry to the full batch of milk and stir gently but thoroughly. Pour into your yogurt maker or fermentation vessel.
Step 5 — Ferment for 36 hours Set the temperature to 100°F (38°C) and ferment for a full 36 hours. The extended fermentation time is critical — this is what makes Dr Davis’s protocol different from standard yogurt making and is what concentrates the bacteria to therapeutic levels.
Step 6 — Refrigerate Transfer to the refrigerator to cool. This thickens the yogurt and improves texture. Store in a sealed container for up to one week.
Tips for Success
- Use fresh, high-quality organic half and half for best results
- Avoid ultra-pasteurized milk — it does not support proper fermentation
- If the yogurt is too runny, increase the prebiotic fiber or use cream instead of milk
- For your next batch, use 2 tablespoons of your finished yogurt as the starter — no need to use tablets again
How to Use L Reuteri Yogurt
- Aim for half to one cup daily
- Add to smoothies, top with fruit and nuts, or use as a base for dips and dressings
- Never heat above 100°F (38°C) — this kills the live bacteria
How Long Does L Reuteri Take to Work?
This is one of the most common questions people ask after starting. The honest answer is that it varies by individual and benefit:
Digestive changes — many people notice reduced bloating and improved digestion within the first 1-2 weeks.
Mood and sleep — oxytocin-related effects on mood and sleep quality are often reported within 2-4 weeks of consistent daily use.
Skin improvements — skin benefits typically become noticeable after 4-8 weeks of consistent use.
Immune and metabolic effects — these take longer to manifest, typically 2-3 months of consistent daily use before meaningful changes are measurable.
The key is consistency. Taking L reuteri occasionally will not restore your microbiome. Daily use over several months is what produces lasting change.
L Reuteri Yogurt Side Effects — Titrating Up Explained
This is something Dr. Davis discusses extensively and something many people experience when they first start: a period of adjustment symptoms when beginning L reuteri supplementation.
When you introduce large numbers of beneficial bacteria into a gut that has been depleted for years, a process called competitive exclusion begins. The L reuteri bacteria start displacing harmful microbes, and as those microbes die off they can release toxins and gases that cause temporary symptoms. This is sometimes called a Herxheimer reaction or die-off response.
Common titrating up symptoms include:
- Bloating and gas — the most common initial symptom
- Loose stools or changes in bowel habits
- Mild cramping or abdominal discomfort
- Temporary increase in brain fog before it clears
- Fatigue in the first few days
These symptoms are generally a sign it is working — not a sign to stop. They typically resolve within 1-3 weeks as your microbiome rebalances.
How to manage titrating up symptoms: Start with a smaller amount — a quarter cup of yogurt per day rather than a full cup — and increase gradually over 2-3 weeks as your body adjusts. This is what “titrating up” means: slowly increasing the dose to allow your gut to adapt without overwhelming it.
If symptoms are severe, reduce the amount further and increase even more slowly. Some people need 4-6 weeks to work up to a full daily serving. This is completely normal and does not mean the product is not right for you.
Most people find that once they get through the initial adjustment period, they feel significantly better than before they started — which is the whole point.
L Reuteri Food Sources
While homemade yogurt is by far the most effective way to get L reuteri, some naturally fermented foods may contain small amounts:
- Certain traditionally fermented yogurts and kefirs — check labels for specific strains
- Some aged cheeses
- Breast milk — L reuteri is naturally present in human breast milk and is one of the primary ways it was passed from generation to generation before modern food processing disrupted this cycle
The concentrations in natural food sources are generally too low to restore depleted populations effectively, which is why the homemade yogurt method is so powerful.
How Much L Reuteri Yogurt Should You Eat Per Day?
Dr. Davis recommends half a cup to one cup of L reuteri yogurt per day as a maintenance dose once you have successfully titrated up. Starting with a quarter cup and working up gradually over 2-4 weeks is the recommended approach for anyone new to it.
There is no established upper limit, and many people consume more than one cup daily without issues. Let your body guide you — if you feel well and your digestion is comfortable, you are likely at the right amount.
Are There Any Side Effects Beyond Titrating Up?
Beyond the initial titrating up period, most people tolerate L reuteri very well with no ongoing side effects. The bacteria is naturally present in the human body and has been for millions of years.
A small number of people with significant gut dysbiosis may take longer to adjust. If you are immunocompromised or have a serious medical condition, consult your healthcare provider before starting any probiotic supplementation.
The Bigger Picture — Gut Health, Glutathione and Immune Function
What the research increasingly shows is that immune health, gut health, and cellular defense are deeply interconnected systems. L reuteri works at the gut level — restoring a critical microbial population that regulates immunity, inflammation, mood, and metabolism.
Glutathione works at the cellular level — protecting every cell in your body from oxidative damage, supporting detoxification, and regulating immune responses at the molecular level. When your gut is inflamed it places constant demand on your glutathione reserves. Restore the gut with L reuteri and you reduce that inflammatory burden. Support your cells with a proven glutathione precursor and you give your immune system the tools it needs to function at its best.
If you haven’t read our complete guide to glutathione and Immunocal yet, it is worth your time — particularly if immune health, healthy aging, or detoxification are part of why you’re researching gut health.
Taking Immune Health Further
L reuteri is a powerful foundation for gut and immune health. For those wanting to support their body’s defenses at the cellular level too, Immunotec has spent 45 years developing products built around glutathione — the master antioxidant your cells produce naturally and depend on for immune function, detoxification, and healthy aging.
Their flagship product Immunocal is the only patented glutathione precursor of its kind, backed by over 90 peer-reviewed clinical studies and listed in the Physicians’ Desk Reference. Many of my customers combine daily L reuteri yogurt with Immunocal as a comprehensive wellness foundation — gut support from the bottom up, cellular support from the inside out.
You can order Immunocal and the full Immunotec product range worldwide at glutathionesales.com. Canadian customers can order directly through my Immunocal Canada affiliate link.
Questions? Call me at 1-833-633-4367, Monday to Friday, 9am to 6pm PST.
— Denise Chapman, Authorized Immunotec Consultant Since 2014, ID #3123749
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Consult a healthcare professional before starting any new supplement, especially if you are pregnant, nursing, taking medications, or have a medical condition.
Items Used in the Complete Guide to L Reuteri
List of Items You Need on Amazon: ( Links supplied)
L Reuteri Yogurt Machine – Must be able to be set for 36 hours at 100F or 38C or this machine: L Reuteri Ultimate
Starter Tablets – L-Reuteri Bacteria
Inulin Powder – feeds the bacteria