A synbiotic is not a “list of bacteria.” It is a combination strategy: probiotics (live microorganisms) plus prebiotics (substrates selectively used by beneficial microbes). Two broad approaches exist: (1) a complementary synbiotic, where the probiotic and prebiotic are chosen to support a similar health goal but the prebiotic is not necessarily designed to feed that exact strain; and (2) a synergistic synbiotic, where the prebiotic is selected specifically to be utilized by the co-administered microorganism to enhance predictability or magnitude of effect. That’s why it is more accurate to ask “which strain + which substrate,” rather than “which synbiotic bacteria.” Common pairings may include Lactobacillus/Bifidobacterium strains combined with fibers such as inulin or fructo-oligosaccharides, but effects depend on the exact formulation, dose, and the individual’s tolerance—especially in conditions where fermentable fibers can increase gas or bloating.