What Is a Synbiotic? ISAPP 2020 Definition, Products, and Evidence (2026)
Updated April 2026 · Sources: ISAPP Synbiotic Consensus 2020, Swanson et al., Nat Rev Gastroenterol Hepatol
The ISAPP 2020 Definition
"A mixture comprising live microorganisms and substrate(s) selectively utilised by host microorganisms that confers a health benefit on the host."
Swanson et al., Nature Reviews Gastroenterology & Hepatology, 2020
Two Types of Synbiotic
The ISAPP 2020 consensus distinguishes two synbiotic categories:
Complementary Synbiotic
The probiotic and prebiotic each independently contribute to the health benefit, but there is no specific requirement that the prebiotic feeds the specific probiotic strain present. Both components work through independent pathways, and the combination is additive rather than synergistic. Most commercial "synbiotics" are complementary rather than true synergistic synbiotics.
Synergistic Synbiotic
The prebiotic specifically feeds the probiotic strain in the product, creating a true synergistic effect. This requires careful matching - the prebiotic should preferentially support the co-administered strain's growth and activity in the colon. This type provides the most theoretically compelling benefit but is harder to demonstrate in clinical trials.
What the Evidence Says for Synbiotics
Constipation and Transit Time
Emerging EvidenceMultiple RCTs show synbiotics outperform standalone probiotics for constipation. A 2020 meta-analysis (Tan et al., J Gastroenterol Hepatol) found synbiotic products significantly improved stool frequency and consistency versus probiotic alone. The prebiotic component (typically inulin or FOS) provides bulk-forming and fermentation substrate that probiotics cannot.
Cite: Tan et al., J Gastroenterol Hepatol 2020
Infant Gut Colonisation
Strong EvidenceThe clearest clinical application of synbiotics is in infant formula. Formula supplemented with both probiotic bacteria (B. longum, L. rhamnosus) and prebiotic GOS more closely mimics the microbiome-shaping effect of breastfeeding than either component alone. Breastfed infants have naturally high Bifidobacterium counts, maintained by HMOs (human milk oligosaccharides) which act as natural prebiotics. GOS is the best commercially available HMO analogue.
Cite: Koletzko et al., Ann Nutr Metab 2018; Vandenplas et al., Nutrients 2015
Immune Function in Elderly
Emerging EvidenceThe elderly microbiome is characteristically less diverse than young adults. Synbiotic supplementation in clinical trials of adults over 65 shows improvements in Bifidobacterium counts and immune markers (NK cell activity, vaccination response). The SYNCAN and AgeProbio trials are landmark RCTs in this space.
Cite: Ouwehand et al., Br J Nutr 2008; Bartosch et al., J Clin Microbiol 2005
Consumer Synbiotic Products: Honest Reviews
Affiliate disclosure: some links below may be affiliate links. Products are evaluated on evidence, not commission.
Seed DS-01 Daily Synbiotic
Emerging EvidencePrice
~$49.99/month
CFU
53.6 billion
Strains
24 strains
Prebiotic
Indian pomegranate
Seed's DS-01 uses a nested capsule design (outer prebiotic layer, inner probiotic capsule) intended to protect strains from stomach acid. Their transparency about strain designations (they publish a "Strain Transparency" document) is commendable. The 24-strain blend covers Lactobacillus, Bifidobacterium, and some less common species. The prebiotic (Indian pomegranate extract) is less well-studied than inulin, FOS, or GOS - Seed's own pilot data is interesting but not fully independently replicated. Premium price is partly brand rather than evidence premium.
Honest verdict: good product, well-made, transparent. Slightly over-priced for the evidence level. Best for: health-conscious adults wanting a premium multi-strain synbiotic with excellent branding and reasonable transparency.
Ritual Synbiotic+
Emerging EvidencePrice
~$44.99/month
CFU
11 billion
Strains
3 strains + postbiotic
Prebiotic
PreforPro (LH01)
Ritual Synbiotic+ combines 3 probiotic strains (LGG, B. animalis subsp. lactis, and L. acidophilus NCFM), a novel prebiotic (PreforPro, a bacteriophage-based prebiotic with some proprietary research), and Tributyrin (a butyrate postbiotic). Including a postbiotic in the formulation is innovative and makes this technically a tribiotic (probiotic + prebiotic + postbiotic). The lower CFU count (11 billion) is less than clinical trial doses for most strains but within range. Ritual's transparency about manufacturing and third-party testing is good.
Honest verdict: innovative formulation including the postbiotic butyrate component. The LGG and NCFM strains have strong individual evidence. PreforPro prebiotic is novel but less studied than inulin. Best for: adults interested in the probiotic-prebiotic-postbiotic synergy concept with moderate CFU needs.
Can You Build Your Own Synbiotic?
Yes. Taking a standalone probiotic supplement (e.g. Culturelle for LGG) alongside a prebiotic food or supplement (e.g. oats for beta-glucan, or acacia fibre supplement) creates a DIY complementary synbiotic. The advantage: you can optimise each component independently and achieve lower cost. The disadvantage: you miss the convenience of a single product and may not achieve the paired strain-prebiotic specificity of a well-designed synergistic synbiotic.
Practical pairing suggestions:
- LGG (Culturelle) + psyllium husk: strong evidence for both; complements LGG's mucosal effects with psyllium's physical bulk-forming.
- B. infantis 35624 (Align) + acacia fibre: IBS-specific probiotic with low-FODMAP prebiotic suitable for IBS patients.
- B. lactis BB-12 + oats (beta-glucan): constipation application; synbiotic effect on transit time.