The simplest way to remember it: probiotics are the microbes; prebiotics are their food. Both support the gut microbiome, but they do opposite jobs — one adds beneficial bacteria, the other feeds the beneficial bacteria you already have. Together with fermented foods they form the toolkit for a healthier gut and, through the gut-brain axis, a steadier mind.

Probiotics: adding microbes

A probiotic is a live microorganism that, in adequate amounts, provides a health benefit. Probiotics come as supplements and in fermented foods, and their effects are strain- and dose-specific.[1] Think of them as introducing specific helpful residents — though most are transient and pass through rather than settling in.

Prebiotics: feeding microbes

A prebiotic is a food component — usually a type of fibre — that your own beneficial microbes ferment, selectively encouraging them to grow. Prebiotic-rich foods include onions, garlic, leeks, asparagus, slightly-green bananas, oats and legumes. When microbes ferment these fibres, they produce short-chain fatty acids like butyrate — the metabolites that signal along the gut-brain axis.[2] In one controlled study, a prebiotic even reduced the waking cortisol response and shifted emotional processing in healthy volunteers.[3]

How they work together (and what a synbiotic is)

Because probiotics are microbes and prebiotics are their food, combining them is logical — a synbiotic is a product that pairs the two, so the added microbes arrive with fuel. Fermented foods, meanwhile, deliver live microbes in a food matrix. None of these replaces the others: prebiotic fibre feeds your whole existing community, which is why fibre is the foundation everything else builds on.

Which do you need?

For most people, prebiotic fibre from a varied plant-rich diet is the highest-leverage starting point, with fermented foods and — where there's a specific goal — a studied probiotic strain on top. Which fibres and strains help you depends on your existing microbiome. Flore tests your gut and builds a synbiotic formula from your own data.