The gut microbiome is one of the most active areas in biology and one of the most oversold in retail. The gap between what is known and what is claimed on a label is unusually wide here.
The thing most labels ignore: strain specificity
This is the single most important concept in the category, and almost nothing on a supermarket shelf respects it.
Bacterial names have three parts. In Lactobacillus rhamnosus GG: genus, species, strain. The effects are specific to the strain, not the species. L. rhamnosus GG has good evidence for particular indications. A different L. rhamnosus strain has not inherited that evidence — it is a different organism with different genes.
A product listing “Lactobacillus rhamnosus” without a strain designation is telling you almost nothing. When you see specific strains named — GG, DSM 17938, CNCM I-745 — the manufacturer is pointing at actual trials.
Where the evidence is genuinely strong
- Antibiotic-associated diarrhoea. The best-supported use. Saccharomyces boulardii and L. rhamnosus GG both reduce incidence meaningfully. Take them a couple of hours apart from the antibiotic.
- Acute infectious diarrhoea in children. Reduces duration, typically by around a day.
- Pouchitis after certain bowel surgery, where specific multi-strain formulations have strong evidence.
- Some IBS symptoms, though results vary considerably by strain and by individual.
- Infant colic, where L. reuteri DSM 17938 has reasonable evidence in breastfed infants.
Where it is weak or absent
General “gut health” in a healthy adult. Immune support. Weight loss. Mood, where the “psychobiotics” research is genuinely interesting and nowhere near ready to sell a product on. Broad-spectrum daily probiotics as preventive maintenance, for which the evidence is thin.
There is also a finding worth knowing: some research suggests probiotics taken after antibiotics can delay the return of a person’s own native microbiome compared with letting it recover on its own. The picture is more complicated than “add good bacteria, get good gut.”
Prebiotics may matter more
Prebiotics are fibres that feed the bacteria you already have — inulin, fructo-oligosaccharides, galacto-oligosaccharides and resistant starch.
There is a reasonable argument that this is the more reliable lever. Feeding your existing microbial community works with an ecosystem already adapted to you, rather than trying to introduce organisms that mostly pass through without colonising.
Food sources: onions, garlic, leeks, asparagus, slightly green bananas, oats, and cooked-then-cooled potatoes or rice, which form resistant starch on cooling.
One caution: inulin and FOS are high-FODMAP and can worsen bloating and pain considerably in people with IBS. If concentrated prebiotics make you feel worse, that is informative rather than a sign to push through.
Fermented food deserves more attention than it gets
A well-conducted trial from Stanford compared a high-fibre diet with a high-fermented-food diet over ten weeks. The fermented food arm increased microbiome diversity and decreased markers of inflammation. The high-fibre arm did not do so to the same degree over that period.
That is one trial and should not be over-read. But it points at something the supplement framing misses: yoghurt, kefir, sauerkraut, kimchi, miso and unpasteurised pickles deliver a broad and varied microbial load alongside the food matrix, for a fraction of the price of a capsule.
Check the label says “live cultures” and that it has not been pasteurised after fermenting, which kills the organisms.
A practical position
- Take a named, evidence-backed strain for a specific indication — especially alongside antibiotics.
- Do not take a broad daily probiotic expecting general benefit; the evidence does not support it.
- Eat fermented foods regularly. Cheaper, better evidenced for diversity, and pleasant.
- Eat more fibre from varied plant sources. This is the foundation, and the part most people skip.
- Persistent digestive symptoms deserve a diagnosis, not a supplement.
Related reading
- Fibre: Soluble, Insoluble, and Which One You Actually Need
- Digestive Enzymes: Who Actually Needs Them
- Green Superfood Powder: What It Does, What It Does Not, and How to Choose One
Greenergy includes probiotics and digestive enzymes alongside its greens. Treat those as a small addition rather than as a therapeutic dose — a dry powder is not the ideal format for live cultures.
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