What it is
Probiotics are live micro-organisms that, in sufficient amounts, provide a specific benefit. Prebiotics are fibres the human gut does not digest and that feed the body's own bacteria (inulin, FOS, GOS). A synbiotic combines the two.
What matters most when recommending a probiotic is the STRAIN: the proven effect of one strain cannot be transferred to another, not even of the same species. Most act in passing and do not settle in the gut, so their effect lasts as long as they are taken.
Probiotics and prebiotics
Two components with different roles:
- PROBIOTICS: live micro-organisms (Lactobacillus, Bifidobacterium, Saccharomyces boulardii) with effects specific to each strain.
- PREBIOTICS: fermentable fibres (inulin, FOS, GOS) that feed the body's own microbiota.
- SYNBIOTIC: probiotics + prebiotics in the same product. It makes sense, but it is not necessary for a probiotic to work.
- THE STRAIN MATTERS: L. rhamnosus GG is not the same as another L. rhamnosus. The evidence refers to specific strains.
At the counter
When to recommend it
- Antibiotic-associated diarrhoea: strains with evidence (S. boulardii, L. rhamnosus GG), starting with the antibiotic
- Choose the strain for the situation, not the brand or the number of strains
- Prebiotics or fibre: for constipation and for the body's own microbiota, starting with a small dose
- Keep up a fibre-rich diet: without it, any effect is smaller
When not to
- Do not use probiotics in severely immunocompromised patients or those with central venous catheters without medical advice
- Do not sell them as a cure-all: each strain has its own use
- Do not ignore product quality (identified strain and count guaranteed until the end of shelf life)
Warnings
- Important IMMUNOSUPPRESSION: in severely immunocompromised patients or those with a central venous catheter, infections caused by the probiotic itself have been described. Only on medical advice.
- Important STORAGE: some probiotics lose viability with heat; follow the conditions on the pack (some need refrigeration).
- Caution STRAIN: you cannot recommend a probiotic 'for irritable bowel' on the evidence of another one 'for diarrhoea'. Check which strain it contains.
- Caution ANTIBIOTICS: take the bacteria about 2 hours apart from the antibiotic; S. boulardii (a yeast) does not need this.
- Worth knowing QUALITY: a serious product identifies the strain and guarantees the count until the expiry date.
Pharmacokinetics
- Absorption
- Probiotics are not absorbed: they act in the gut. Neither are prebiotics: they are fermented in the colon.
- Distribution
- Some fermentation products (such as butyrate) are absorbed and have effects beyond the gut.
- Metabolism
- Prebiotics are fermented in the colon, producing short-chain fatty acids and gas (hence the wind when starting).
- Elimination
- Most probiotics are cleared within days or weeks of stopping: their effect lasts as long as they are taken.
Probiotics vs prebiotics
| Aspect | Probiotics | Prebiotics |
|---|---|---|
| What they are | Live micro-organisms | Fibre that feeds the microbiota |
| What matters | The specific strain | The type of fibre and the dose |
| Typical effect | Specific to each strain (e.g. antibiotic diarrhoea) | Bowel habit, and food for the body's own microbiota |
| Side effect | Uncommon | Wind at first |
| Duration of effect | While taken | While taken |
They do not compete: they are chosen according to the goal. A synbiotic combines them, but what decides whether a probiotic works is its strain.
Self-assessment
Three questions. When you check your answers you will see the explanation for each one.
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Synbiotic = probiotics (micro-organisms) + prebiotics (fibre that feeds them) in the same product.
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Effects are proven strain by strain. More strains does not mean more efficacy.
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Most commercial strains are cleared days or weeks after stopping. That is why the effect depends on continuing to take them.
Training content. It does not replace the summary of product characteristics or clinical judgement.