Lactobacillus reuteri
A species we co-evolved with that's been disappearing from modern guts. Specific strains have strong evidence for infant colic, oral health, and mood.
Strong evidence for: infant colic reduction (DSM 17938 — multiple RCTs), gum health and gingivitis reduction (Prodentis), LDL cholesterol reduction (NCIMB 30242). Emerging evidence for oxytocin elevation / social bonding effects from animal work (Kassel et al.). Effects: days for colic, weeks for cholesterol.
Lactobacillus reuteri (now reclassified as Limosilactobacillus reuteri) is one of the few species that's a native human gut commensal — it lived in nearly everyone's microbiome a century ago and now appears in fewer than 10% of people, probably due to antibiotics, processed food, and sanitation. Different strains have different uses. DSM 17938 is the most-studied for infant colic (genuine 50%+ reduction in crying). NCIMB 30242 lowers LDL cholesterol. ATCC PTA 5289 supports oral health (Prodentis). And L. reuteri yogurt protocols (William Davis, Super Gut) re-establish the strain in adults at very high colony counts.
- Form
- BioGaia Protectis (DSM 17938) — infant colic, general gut. BioGaia Prodentis (ATCC PTA 5289) — oral / gum health. Cardioviva (NCIMB 30242) — cholesterol. Home-fermented L. reuteri yogurt (William Davis protocol) — very high colony counts.
- Dose
- 100 million to 10 billion CFU/day depending on strain and use case. Read product label.
- Timing
- With food. Daily.
- Schedule
- Daily for 4–12 weeks for colonisation; longer for some uses.
- Side effects
- Mild gas, bloating, GI changes in the first 1–2 weeks. Generally well-tolerated.
- Interactions
- Take 2 hours apart from oral antibiotics. Otherwise clean.
- Contraindications
- Severe immune compromise. Central venous catheter (rare bacteremia risk). Pancreatitis (caution).
- Lab markers
- Lipid panel for NCIMB 30242. Symptom tracking for colic, oral health.
- Food sources
- Some fermented dairy (kefir, yogurt with reuteri strains specifically). Most modern dairy doesn't contain reuteri unless specifically inoculated.
Pairs with
Saccharomyces boulardii, L. rhamnosus GG (broader probiotic stack). Prebiotics (inulin, lactose if tolerated — for the home yogurt protocol). Vitamin D, vitamin C for immune-supportive contexts.
within Probiotics & gut