Probiotics 101: How to Pick One That Actually Works

The probiotic aisle is chaos. Strain numbers, CFU counts, prebiotics, postbiotics… here's a no-nonsense guide to picking the right one.

Walk down the probiotic aisle and you'll see 50 billion CFU, 20 strains, refrigerated, shelf-stable, with prebiotics, with postbiotics. Most of it is noise. Here's what actually matters.

What probiotics do (and don't do)

Probiotics are live bacteria that, in adequate amounts, may confer a health benefit. Strong evidence supports their use for:

• Antibiotic-associated diarrhea prevention
• IBS-D and IBS-C symptom management
• Some forms of eczema
• Possibly mood (via the gut-brain axis)
• Mild reductions in bloating

Weaker evidence: weight loss, mood, allergies, general 'wellness'.

CFU counts: more isn't always better

CFU = colony-forming units. Most useful products contain 10–50 billion CFU per dose. Beyond that, more doesn't mean better — it can even cause side effects (gas, bloating) initially.

The strains matter more than the count

Specific strains have specific evidence. Look for:

• L. rhamnosus GG — antibiotic-associated diarrhea
• S. boulardii — traveller's diarrhea, C. diff prevention
• L. plantarum 299v — IBS bloating
• L. helveticus R0052 + B. longum R0175 — mood and stress
• B. infantis 35624 — IBS

What to look for on the label

• Specific strain numbers (e.g. L. rhamnosus GG, not just 'L. rhamnosus')
• Guaranteed CFU at expiration, not at manufacture
• Refrigeration or shelf-stable testing — both can work
• Enteric coating or delayed release (helps survive stomach acid)

When to take them

Most are best taken with food, especially a meal with some fat. Once daily is enough for most people.

Don't forget prebiotics

Prebiotics are the fibre that feeds your existing gut bacteria. Often more impactful than probiotics alone. Sources:

• Garlic, onions, leeks
• Asparagus
• Oats and bananas (slightly green)
• Legumes
• Inulin or PHGG supplements

Bottom line

Pick a multi-strain product (10–50 billion CFU) with documented strain numbers, take it consistently for 4–8 weeks, and pay attention to how your body responds. If nothing changes, switch strains or try a prebiotic.

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