Microbiome science

Synbiotics

Also called: combined probiotic and prebiotic

A synbiotic combines a probiotic strain with a prebiotic that selectively feeds it. The logic is sound: arrive in the gut with food and the bacteria might colonise better. Real-world evidence for synbiotics outperforming the probiotic alone is mixed and depends entirely on whether the strain-prebiotic pair is well-matched. Most consumer 'synbiotic' products are loosely combined and don't show extra benefit.

Two types of synbiotic

  • Complementary (per ISAPP 2020, Swanson et al, Nat Rev Gastroenterol Hepatol): probiotic and prebiotic each independently meet their own definition (live microbe with health benefit + selectively-utilised substrate); the two are not specifically matched.
  • Synergistic (per ISAPP 2020): the substrate is selectively utilised by the co-administered live microbe. Doesn't require the substrate to qualify as a prebiotic on its own.
  • Example synergistic pair: Bifidobacterium with FOS (fructo-oligosaccharide), bifidobacteria preferentially ferment FOS.

What the evidence shows

  • Synergistic synbiotics for IBS: small benefit over probiotic alone in some trials.
  • Synbiotics in infants: improve gut barrier markers and reduce eczema risk modestly.
  • Synbiotics post-antibiotic: faster recovery of microbiome diversity than probiotic alone in some studies.
  • Synbiotics for general adult gut health: evidence is thin. Most data is industry-funded.

Honest assessment

  • If you're going to take a probiotic anyway, a well-matched synergistic synbiotic might marginally improve effect.
  • Don't pay much extra for 'synbiotic' on the label without the strain + prebiotic specifically matched.
  • Cheaper alternative: take a defined probiotic strain alongside dietary fibre and fermented foods. Same effect, lower cost.
  • For specific clinical situations (IBS, post-antibiotic, infant colic), strain-matched synbiotics are reasonable.

Common questions

Is a synbiotic better than a probiotic?
Sometimes, modestly, when the strain and prebiotic are deliberately matched. Most consumer products are loosely combined and the benefit over a quality probiotic is small. Look for specific strain-prebiotic pairings with published trials.
Can I make my own synbiotic?
Yes. Take a probiotic capsule with breakfast that includes prebiotic foods (oats, banana, onion, garlic). Functionally similar to most consumer synbiotics at a fraction of the cost.
What's the dose of a synbiotic?
Match the probiotic dose to the strain's evidence base. Most synbiotic products use 1 to 50 billion CFU + 2 to 5 g of prebiotic fibre. Higher fibre doses can cause initial gas; build up.

Sources