Probiotics: What They Are, What They Do and Which Are the Best

Probiotics: What They Are and What They Do

The World Health Organization (WHO) defines probiotics as "live microorganisms that, when administered in adequate amounts, confer a health benefit on the host." In short: bacteria (and sometimes yeasts) that, when consumed in sufficient quantity, do something good for your body.

The probiotic market has exploded. In Spain alone, annual sales exceed €200 million. But the reality is that most probiotics sold don't work the same way for everyone — and many consumers buy them without knowing which strain they need or whether it's right for their situation.

How probiotics work

• Competition for adhesion: they occupy binding sites on the intestinal mucosa, physically blocking pathogenic bacteria.
• Antimicrobial substances: bacteriocins, hydrogen peroxide, and organic acids that inhibit pathogen growth.
• Immune modulation: stimulate secretory IgA production, modulate dendritic cells, and regulate Th1/Th2/Treg balance.
• Intestinal barrier strengthening: increase expression of tight junction proteins (claudins, occludin) that seal the intestinal lining.
• Metabolite production: some probiotics produce short-chain fatty acids, vitamins, and neurotransmitters.
• Gut-brain axis communication: influence serotonin and GABA production, with effects on mood and stress.

Proven probiotic benefits

High evidence (multiple controlled clinical trials):

• Reduction of antibiotic-associated diarrhea (especially Lactobacillus rhamnosus GG and Saccharomyces boulardii)
• Prevention and treatment of Clostridium difficile diarrhea
• Reduction of IBS symptoms
• Improvement of lactose intolerance (Lactobacillus acidophilus, Bifidobacterium longum)
• Reduced duration of respiratory infections
• Improvement of atopic dermatitis in children

Moderate evidence:

• Symptom improvement in inflammatory bowel disease (ulcerative colitis)
• Reduction of inflammation markers
• Mood improvement and anxiety reduction (psychobiotics)
• Weight loss support (Lactobacillus gasseri)
• LDL cholesterol reduction

Best probiotics: a strain-by-strain guide

This is the critical point most guides miss: probiotic benefits are strain-specific. Lactobacillus acidophilus NCFM is not the same as Lactobacillus acidophilus La5 — same genus and species, but different properties.

• Lactobacillus rhamnosus GG (LGG): the world's most studied probiotic. Reduces antibiotic diarrhea, improves IBS, strengthens the intestinal barrier.
• Bifidobacterium longum BB536: reduces allergic symptoms, improves constipation, and boosts immunity.
• Lactobacillus acidophilus NCFM: improves lactose digestion and reduces abdominal bloating.
• Bifidobacterium infantis 35624: particularly effective for IBS; reduces abdominal pain, gas, and distension.
• Saccharomyces boulardii CNCM I-745: probiotic yeast; highly effective for traveler's diarrhea and antibiotic-associated diarrhea. Antibiotic-resistant, so it can be taken simultaneously.
• Lactobacillus plantarum 299v: effective for diarrhea-predominant IBS; reduces gas and abdominal pain.
• Akkermansia muciniphila: the rising star of the microbiome. Strengthens the intestinal barrier and shows promising metabolic effects (weight, blood sugar). Now available as a pasteurized supplement.

How to choose a good probiotic

1. Identified strains: the label must specify the full strain name (genus + species + strain code), not just "Lactobacillus spp."
2. CFU per dose: most studies use 1-10 billion CFU (10⁹-10¹⁰). More isn't always better; it depends on the strain and condition.
3. Guaranteed viability: bacteria must be alive at the point of consumption, not just at the time of manufacture. Look for guaranteed viability until the expiry date.
4. Gastric protection: enteric-coated capsules or microencapsulation technology protect bacteria from gastric acid.
5. Compatibility with your microbiota: the ideal probiotic depends on your current microbiota composition.

Natural probiotics: the best food sources

• Kefir: king of probiotic foods. Up to 60 different bacterial and yeast strains. Can be made at home.
• Natural yogurt: always with "live Lactobacillus bulgaricus and Streptococcus thermophilus" on the label. Avoid those pasteurized after fermentation.
• Unpasteurized sauerkraut: rich in Lactobacillus plantarum. Only the refrigerated kind, not shelf-stable jars.
• Kimchi: Korean version with various fermented vegetables and spices. Rich in Lactobacillus kimchii.
• Miso: Japanese fermented soybean paste. Source of Aspergillus oryzae and lactic acid bacteria. Add at the end of cooking — heat destroys bacteria.
• Tempeh: fermented pressed soy. Besides probiotics, an excellent plant protein source.
• Kombucha: fermented tea. Source of acetic acid, gluconic acid, and various bacterial strains.

When and how to take probiotics

• Timing: with breakfast or immediately before a main meal. Gastric pH rises with food, improving bacterial survival.
• With antibiotics: always separate by at least 2 hours. Exception: Saccharomyces boulardii can be taken at any time (it's a yeast, antibiotics don't affect it).
• Duration: minimum 4-8 weeks to see results. Probiotics don't permanently colonize; their effects last while you take them and a few weeks after.