Everything science knows about probiotics — from definition to practical use. With interactive quiz, comparison table and verified references.
The World Health Organization (WHO, 2001) defines probiotics as live microorganisms that provide a health benefit on the host when consumed in adequate amounts.¹ Each living microbe is called by its full strain designation, because the health benefits when consumed depend entirely on which strain is used. The term covers probiotic bacteria from the Lactobacillus and Bifidobacterium genera, as well as yeasts like Saccharomyces boulardii. Through food or supplementation, these organisms can provide health benefits that complement a balanced diet.²
Bacteria and yeasts that act directly in the gut. The effect is strain-specific: L. rhamnosus GG has different properties from a generic L. rhamnosus.³
Substrates like inulin and fructo-oligosaccharides (FOS) that selectively nourish beneficial gut bacteria. They amplify the effect of probiotics.⁴
Short-chain fatty acids (butyrate, propionate), antimicrobial peptides and enzymes produced by probiotic activity. An emerging research field.⁵
A combination of probiotics and prebiotics in one formula. The synergy improves colonisation and efficacy according to several meta-analyses.⁶
The probiotic is ingested as a capsule, sachet or fermented food. Gastric protection determines how many bacteria survive the stomach's acidity.
Without enteric coating, up to 90% of live cultures are destroyed by stomach acid (pH < 2). The capsule technology is therefore critical.⁷
The bacteria reactivate in the small intestine, adhere to the gut lining and compete with pathogens for nutrients and space.⁸
Production of lactic acid, strengthening of the intestinal barrier, modulation of the immune system and production of short-chain fatty acids. Action begins within hours.⁹
Our gastrointestinal tract — the human gut — harbours approximately 100 trillion microorganisms: bacteria, yeasts and fungi, collectively known as gut microbes.¹⁰ This complex ecosystem plays a central role in gut health, digestion, immunity and vitamin synthesis. Among the common species found in most people, some are beneficial while others can be bad for the host when they overgrow. A healthy microbiome is characterised by its diversity: the more varied the gut flora, the more resilient the body.¹¹
The gut microbiome contributes to digestion of dietary fibre, production of vitamins (B12, K2), regulation of the immune system — approximately 70% of immune cells reside in the gut — and communication with the brain via the gut-brain axis.¹² It also influences energy metabolism, body weight and even mood. The balance of gut flora is therefore a fundamental parameter of overall health.
Eliminate beneficial bacteria alongside pathogens — the gut flora can take months to recover.¹⁴ A supportive probiotic treatment is frequently recommended.
Increases intestinal permeability and promotes pathogenic bacteria through cortisol.¹⁵ The impact on mental health partly occurs via the gut-brain axis.
A diet low in fibre and high in refined sugars reduces bacterial diversity. Ultra-processed foods are particularly harmful to the microbiome.¹⁶
Bacterial diversity naturally decreases from age 65. Regular probiotic courses can help maintain the balance of gut flora.¹⁷
The effectiveness of a probiotic depends primarily on the strain used — not simply the genus or species. Among the Lactobacillus species, for example, each strain has unique properties documented by specific clinical trials. Here are the most thoroughly researched families in the scientific literature.¹⁸
| Family | Key Strains | Characteristics | Documented Indications |
|---|---|---|---|
| Lactobacillus | L. acidophilusL. rhamnosus GGL. reuteriL. plantarumL. casei | Lactic acid bacteria natural to the digestive system. Produce lactic acid that inhibits harmful bacteria. | Antibiotic-associated diarrhoea¹⁹ (L. rhamnosus GG), urinary tract infections²⁰ (L. reuteri), lactose intolerance²¹ (L. acidophilus), intestinal barrier²² (L. plantarum) |
| Bifidobacterium | B. longumB. bifidumB. breveB. infantisB. lactis | Dominant bacteria in infants. Ferment prebiotic fibres. B. longum, B. bifidum and B. lactis are the best-documented strains in adults. | Irritable bowel syndrome²³ (B. infantis), inflammatory bowel disease — support²⁴ (B. bifidum), regular transit²⁵ (B. lactis) |
| Streptococcus | S. thermophilus | Used in yogurt production. Aids lactose digestion and strengthens the intestinal barrier. | Lactose digestion²⁶, immune stimulation |
| Saccharomyces | S. boulardii | Unique probiotic yeast. Remains active during antibiotic use — antibiotics target bacteria, not yeasts. | Antibiotic-associated diarrhoea²⁷, traveller's diarrhoea²⁸, C. difficile infection²⁹ |
Probiotics work through three main mechanisms: microbiome regulation, intestinal barrier strengthening and immune function modulation.³¹ Multiple systematic reviews have stated that these beneficial effects extend across digestive health and inflammation management. Here are the key documented benefits — with the level of evidence for each.
Probiotics support nutrient absorption and transit regulation. A multi-strain formula helps prevent constipation, diarrhoea and bloating. Convergent meta-analyses.³²
Certain strains stimulate IgA antibody production and activate NK cells. A 2024 systematic review (10 RCTs, 1,560 participants) shows that lactobacilli significantly improve vaccine response in older adults.³³
B. infantis and L. rhamnosus may alleviate symptoms such as abdominal pain and bloating after 6–8 weeks. A 2023 meta-analysis of 82 randomized controlled trials (10,332 patients) confirms the efficacy of certain probiotic combinations.³⁴
Via the gut-brain axis, certain strains influence serotonin and GABA production. A 2025 meta-analysis (23 RCTs, 1,401 patients) shows a significant reduction in depressive symptoms (SMD: −0.96) and a moderate reduction in anxiety (SMD: −0.59).³⁵
Lactobacilli play a dominant role in healthy vaginal flora. L. rhamnosus and L. reuteri show efficacy in preventing recurrent urinary tract infections and bacterial vaginosis.³⁶
Via the gut-skin axis, probiotic strains may ease inflammatory conditions like atopic dermatitis (eczema) and acne. Encouraging preliminary studies, particularly in infants.³⁷
L. gasseri SBT2055 was associated with a modest reduction in visceral fat in a double-blind trial.³⁸ Not a substitute for a balanced diet and regular physical activity.
Beyond these primary areas, emerging evidence points to potential beneficial effects on blood pressure, upper respiratory tract infections and conditions such as ulcerative colitis and Crohn's disease. In neonatal care, certain strains have shown promise for reducing the risk of necrotizing enterocolitis in premature infants.⁴⁵ Researchers have also explored whether probiotics could support immune resilience during COVID-19, though results remain preliminary.
Many RCTs include fewer than 200 participants — generalisability remains limited.
Most clinical trials last 4 to 12 weeks. Long-term effects are poorly documented.
Every person's microbiome is unique — the response to the same strains varies considerably.³⁹
Positive studies are published more frequently — negative results remain under-represented.
There is no universal formula — effectiveness depends on strain selection, colony forming units (CFU) dosage and individual circumstances.⁴⁰ Not all probiotic products are equally helpful, as probiotic supplements are not required to demonstrate clinical efficacy before sale — only safety and labelling are regulated. Here are the 5 essential quality criteria to check before purchasing a probiotic supplement.
The recommended daily dose is at least 10 billion CFU for prevention. For antibiotic-associated conditions, studies recommend 25 billion+.⁴¹
Multiple documented strains that don't inhibit each other.⁴² Multi-strain for prevention, single-strain for specific indications.
Enteric coating is essential — without protection, up to 90% of live cultures don't survive gastric passage.⁷
Each strain should have been tested in at least one published RCT (randomised controlled trial).⁴³
CFU count must be guaranteed until the expiry date, not just at the time of manufacture. Freeze-dried strains offer the best stability at room temperature. Store below 25°C, away from light.⁴⁴
3 questions · about 1 minute
FloraPro 7 contains 7 carefully selected strains from the Lactobacillus, Bifidobacterium and Streptococcus families. With 25 billion CFU per enteric-coated HPMC capsule and freeze-dried cultures, it meets all 5 quality criteria detailed above.
⚠️ Dietary supplement. For specific medical conditions, consult a healthcare professional.
Effectiveness doesn't depend solely on strain selection — the timing, dosage and storage directly influence how many live cultures actually reach the gut. Poor intake can reduce the effect by up to 90%.⁴⁶
First detectable changes in microbiome composition. Don't stop early.
Documented symptom reduction in clinical trials. Tangible results.
Optimal duration for irritable bowel syndrome and chronic digestive issues.
Strains don't establish permanently — they disappear after stopping.⁴⁸ Regular courses are necessary.
Before the era of dietary supplements, probiotics came exclusively from food. Fermented dairy products such as yogurt, kefir and milk-based drinks have been part of daily life and nutrition for centuries. These foods remain an important source of beneficial live microorganisms with recognised nutritional value. However, their concentration and diversity have limits.⁴⁹
| Food | Strains Present | Concentration | Advantage |
|---|---|---|---|
| Yogurt | S. thermophilusL. bulgaricus | 10⁶–10⁸ CFU/g | Accessible, daily, well tolerated |
| Kefir | L. kefiriVarious yeasts | 10⁷–10⁹ CFU/ml | Great strain diversity |
| Raw sauerkraut | L. plantarumL. brevis | 10⁶–10⁸ CFU/g | Rich in prebiotic fibres |
| Kimchi | L. plantarumLeuconostoc | 10⁷–10⁹ CFU/g | High diversity, vitamins |
| Kombucha | GluconobacterYeasts | Variable | Drink, easy to integrate |
| Miso | AspergillusLactobacilli | Variable | Amino acids, umami |
Probiotics are considered safe for the vast majority of healthy individuals. Side effects are rare and generally transient.⁵¹
During the first 5–7 days, mild digestive discomfort, bloating or gas may occur — these are not a sign of digestive disorders but indicate that the microbiome is adapting to the new strains. They resolve spontaneously in the vast majority of cases. If discomfort persists beyond two weeks, consult with a healthcare provider and report any unusual reaction. People with underlying health conditions should schedule an appointment with their doctor before starting any probiotic course.
Immunocompromised patients (chemotherapy, transplant, advanced HIV) have a rare but documented risk of bacteraemia. Medical consultation mandatory.⁵² In Switzerland, the gastroenterology departments at Inselspital Bern and University Hospital Zurich (USZ) are reference centres for complex cases.
Data is reassuring for most studied strains, but consult your doctor as a precaution, especially in the first trimester.
Specific strains are documented for infants, but prescription must be supervised by a paediatrician.⁴⁵
Immunosuppressants: consult your doctor. Antifungals: may reduce the efficacy of S. boulardii. Antibiotics: S. boulardii can be taken simultaneously.
In Switzerland, the regulatory framework for probiotics differs from that of the European Union. Understanding these specifics enables informed choices.⁵³
The Federal Food Safety and Veterinary Office (FSVO) regulates dietary supplements in Switzerland under food law. An FSVO-compliant product guarantees that all label claims are scientifically substantiated — unauthorised health claims are prohibited.
A probiotic marketed as a dietary supplement does not need to prove therapeutic efficacy before market launch (unlike a Swissmedic-registered medicine). This is why the clinical documentation of strains is a decisive selection criterion.
Probiotics as dietary supplements are not covered by mandatory health insurance (KVG/LAMal). Prices range from 25 to 60 CHF per month. Some supplementary insurance policies (VVG/LCA) may partially reimburse — check your individual policy.
Favour products manufactured in Switzerland with documented quality control, FSVO compliance, strains identified on the label with CFU count per strain, and viability guaranteed until expiry date.
For international reference, the National Institutes of Health (NIH) and its National Center for Complementary and Integrative Health (NCCIH), the Mayo Clinic and Harvard Medical School all provide expert resources on probiotics. In the United States, the Food and Drug Administration (FDA) classifies most probiotics as dietary supplements — a national regulatory approach similar to the Swiss framework.
Probiotics are live microorganisms — bacteria or yeasts — that confer a health benefit when consumed in adequate amounts (WHO, 2001). The most studied genera are Lactobacillus, Bifidobacterium and Saccharomyces boulardii. The effect is always strain-specific. For education on strains and dosage, expert resources are available from major health services; for personalised advice, consult your healthcare provider. More in Section 1.
Probiotics are beneficial live microorganisms. Prebiotics are non-digestible fibres (inulin, FOS) that feed the good bacteria already in your gut. The two are complementary, and their combination (synbiotic) is more effective than either alone.
At least 10 billion CFU per day for prevention. For antibiotic-associated diarrhoea, 25 billion+. A higher dose isn't automatically better — enteric coating is equally important. Details in Section 5.
Optimal intake is during a meal with a glass of water at room temperature. Food buffers stomach acid and protects the bacteria. Avoid hot drinks (>40°C). Consistency matters more than exact timing. See Section 6.
Minimum 4 weeks for a measurable effect. For IBS, 8–12 weeks. Strains don't permanently colonise the gut — regular intake is necessary to maintain the balance of gut flora.
B. infantis, B. breve and L. reuteri are documented for infants. Paediatric consultation is mandatory. Never use adult-dosed preparations in children.
Side effects are mild and transient: digestive discomfort, bloating or gas in the first days. These reactions resolve within 5–7 days. Immunocompromised individuals must consult a doctor. In regulatory terms, probiotics are not intended to treat disease but to support general wellbeing. Details in Section 8.
Yes, and it's even recommended. Starting simultaneously significantly reduces the risk of antibiotic-associated diarrhoea. S. boulardii is unaffected by antibiotics (yeast, not bacteria). Continue the course for 4 weeks after the antibiotics end.
What science establishes — and what remains open.
