ORS first, then strain-specific probiotic support if antibiotics or diarrhea risk justify it. BRAT, sports drinks, broth-as-therapy, glutamine, and routine adult zinc do not earn the slot.Stack-kit editorial
For an acute stomach bug, the single highest-yield move is reduced-osmolarity oral rehydration solution (245 mOsm/L: 75 mmol/L sodium, 75 mmol/L glucose) — it cuts stool output, vomiting, and the need for IV fluids versus the old WHO formula and versus plain water or sports drinks. Add Saccharomyces boulardii CNCM I-745 (250–500 mg twice daily, ~10⁹–10¹⁰ CFU), which shortens acute diarrhea by roughly 20 hours and cuts antibiotic-associated diarrhea risk by about half. Then refeed early with normal food — the BRAT diet is obsolete and slows recovery. Everything below is sequenced by phase, with the popular options the evidence does not support flagged honestly.
The protocol (by phase)
Phase 1 — Reduced-osmolarity ORS, hours 0–24
Reduced-osmolarity oral rehydration solution
This is where almost all the benefit lives. Diarrheal illness harms through fluid and electrolyte loss, not because plain water is missing. The glucose-coupled sodium co-transport mechanism pulls water across the gut wall even while the gut is inflamed, which is why reduced-osmolarity ORS beats plain water, most flavored electrolyte powders, and sports drinks.
| Item | Dose · timing | Mechanism | Evidence | What to cut |
|---|---|---|---|---|
| Reduced-osmolarity ORS | Sip 50–100 mL every 5–10 min; replace ~200–400 mL per loose stool | Glucose-coupled sodium co-transport pulls water across the gut wall | Hahn, BMJ 2001: lower stool output, vomiting, and IV-fluid need vs standard ORS | Plain water; sports drinks |
| S. boulardii CNCM I-745 | 250–500 mg 2×/day, start day 1, continue through recovery | Yeast unaffected by antibiotics; supports brush-border enzymes and degrades C. diff toxins | Feizizadeh 2014: acute diarrhea duration down ~19.7 h; McFarland 2010: adult AAD RR 0.47 | Generic strain-hidden probiotics |
Phase 1/3 — S. boulardii CNCM I-745
Saccharomyces boulardii CNCM I-745
S. boulardii earns its place because the strain is specific and the use case is narrow. It is a live yeast, not a bacterium, so antibacterial drugs do not kill it. For viral gastroenteritis, the strongest signal is shorter diarrhea duration. For antibiotic-associated diarrhea, adult data show roughly half the risk versus placebo. That is not a generic "microbiome rebuild" claim; it is a strain-specific diarrhea-risk tool.
Phase 2 — Refeed, day 1–3
Begin eating within about 4–12 hours of starting rehydration, as soon as you can keep fluids down. Do not wait for diarrhea to fully stop.
Eat a normal, age-appropriate diet. Early refeeding shortened diarrhea and improved nutritional recovery, with no increase in vomiting, persistent diarrhea, or IV-fluid need versus delayed refeeding. Start with starches, lean protein, cooked vegetables, soups, and yogurt; add fat and fiber back over 24–48 hours as tolerated. Routine lactose avoidance is unnecessary for most adults.
Phase 3 — Optional LGG, day 3 onward / post-antibiotic
Lactobacillus rhamnosus GG ATCC 53103 (optional)
If the trigger was antibiotics, this phase matters most; for a viral bug, the gut typically self-restores once you are eating. L. rhamnosus GG is a reasonable adjunct at ≥10¹⁰ CFU/day, but the honest caveat is important: LGG reduced antibiotic-associated diarrhea overall and significantly in children, while the adult subgroup did not clearly separate from placebo except in H. pylori eradication contexts. Use it as optional, not primary.
What to skip (and why)
The BRAT diet. Bananas, rice, applesauce, and toast are too restrictive and nutritionally inadequate. A normal diet shortens illness; BRAT delays it.
Bone broth as rehydration or gut healing. Broth can be comforting, but it is not an ORS. Sodium content is uncontrolled and usually far below an ORS load, and collagen does not "heal the gut lining" after being digested like any other protein.
L. rhamnosus GG as the adult primary item. For adults after antibiotics, S. boulardii has the stronger data. LGG is optional.
Glutamine. Evidence is real but narrow: critical illness and cancer-therapy populations, not otherwise healthy adults with routine acute diarrhea. Skip it for a routine stomach bug.
Safety and who should skip
Anti-motility drugs are not for everyone. Avoid loperamide entirely with fever, bloody or mucoid stool, or suspected C. difficile. It is appropriate only for immunocompetent adults with non-bloody, non-febrile watery diarrhea and should be stopped if symptoms persist beyond 48 hours.
See a clinician — do not self-treat at home — if: severe dehydration signs, blood in stool, fever above 39 °C / 102 °F, diarrhea lasting more than about 7 days, severe abdominal pain, pregnancy, immunocompromise, age over 65, or inflammatory bowel disease.
S. boulardii is a live yeast. Do not use it in immunocompromised patients, people with central venous catheters, or the critically ill; rare fungemia has been reported in these groups.
Zinc is pediatric/clinician-guided here. WHO zinc dosing for diarrhea is a child and malnutrition-context intervention. Routine adult zinc is not recommended on this page.
FAQ
What should I buy first?
Reduced-osmolarity ORS. If you took antibiotics or diarrhea is still active, add S. boulardii CNCM I-745. LGG is optional and lower priority for adults.
Why not sports drinks?
Most sports drinks are built for sweat, not diarrhea: too little sodium and too much sugar for glucose-coupled sodium transport. ORS is a chemistry spec, not a hydration vibe.
When should I eat again?
As soon as you can keep fluids down, usually within 4–12 hours of rehydration. Waiting for diarrhea to fully stop is outdated advice.
Do I need a probiotic after a viral stomach bug?
Maybe not. For a viral bug, hydration and early refeeding carry most of the benefit. S. boulardii is more compelling when diarrhea is active or antibiotics are involved.
How we'd buy it
Oral rehydration solution: buy a product that states the reduced-osmolarity / WHO formula on the label: about 245 mOsm/L and about 75 mmol/L sodium. Single-serve powder sachets mixed into a measured volume of water are most reliable.
S. boulardii CNCM I-745: look for the named strain "CNCM I-745" on the label, 250 mg per capsule, dosed to 250–500 mg twice daily.
L. rhamnosus GG (optional): strain "GG" or ATCC 53103 at ≥10 billion CFU/serving, guaranteed through expiry.
Citations
1. Hahn S, Kim Y, Garner P. BMJ 2001;323:81–85 — reduced-osmolarity ORS lowered stool output, vomiting, and IV-fluid need.
2. WHO/UNICEF. Reduced-osmolarity ORS formula adopted 2003 — Na⁺ 75, glucose 75, K⁺ 20, citrate 10, Cl⁻ 65 mmol/L; 245 mOsm/L.
3. McFarland LV. World J Gastroenterol 2010;16(18):2202–2222 — S. boulardii adult AAD RR 0.47.
4. Feizizadeh S, Salehi-Abargouei A, Akbari V. Pediatrics 2014;134(1):e176–e191 — acute diarrhea duration reduced by about 19.7 h.
5. Gregorio GV, Dans LF, Silvestre MA. Cochrane 2011, CD007296 — early refeeding shortened illness without increasing vomiting or persistent diarrhea.
6. Szajewska H, Kołodziej M. Aliment Pharmacol Ther 2015;42(10):1149–1157 — LGG overall RR 0.49; adult subgroup non-significant.
7. Shane AL, et al. (IDSA). Clin Infect Dis 2017;65(12):e45–e80 — anti-motility agents contraindicated with fever, bloody stool, or invasive pathogens.
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