Often the best answer is “both—sequenced and dosed correctly.” Prebiotics act as substrates for beneficial microbes and can be powerful for long-term ecosystem shaping. Probiotics, when matched to the right strain and goal, may deliver faster, targeted effects (e.g., post-antibiotic diarrhea risk, certain IBS symptoms). If dietary fiber intake is very low, adding probiotics alone may have limited impact because the underlying ecosystem support is weak. Conversely, rapidly increasing prebiotic fibers can worsen bloating in some individuals, so gradual titration and choosing better-tolerated fibers matters. A practical strategy is: (1) build the nutrition foundation (vegetables, legumes, whole grains, nuts), (2) if symptoms exist, run a 2–4 week probiotic trial matched to the goal, and (3) if tolerated, strengthen durability with prebiotic support. Synbiotic products can be a convenient option for some. The right choice depends on symptoms, tolerance, lifestyle, and coexisting conditions.