I believe I heard this analogy at an Institute for Functional Medicine conference and it helped me understand the concept of Prebiotics and Probiotics so much better, so I'd like to share it with you.
Think of your gut microbiome as a community. Your resident bacteria are considered the community members. They are full time residents and are extremely important in the health of the local economy and keeping it running.
Probiotics are active bacterial cultures found in supplements or in foods such as yogurt, Sauerkraut and Kimchi. In this analogy, think of them as tourists. They are beneficial in supporting the local community/economy, but they are only temporary. They don't repopulate the community, they are only there for as long as you are taking the probiotic supplement or eating the probiotic food. After 1-2 weeks of stopping these supplements, they are no longer detectable in comprehensive stool testing.
Prebiotics are foods and supplements that are in high fiber and resistant starch. Your resident bacteria (your community members), prefer to ferment these prebiotics over other types of food. This helps support their bacterial strength and diversity. The end products of bacterial fermentation include short chain fatty acids (SCFA). SCFA are extremely important for the health of your gut, your gut lining and preventing disease. Even in lowering your risk of colon cancer. So if your diet is low in prebiotics, your resident bacteria will suffer and then as a result your gut health could suffer.
I hope this analogy helps you better understand the difference between Probiotics and Prebiotics and why they are both beneficial. This analogy is why, when I am asked which is more important - prebiotics or probiotics, my answer is prebiotics. Probiotics are still very beneficial, especially for anybody who is trying to heal gut issues, has Inflammatory Bowel Disease, can't tolerate high fiber/starchy foods or is on a round of antibiotics. But for long term gut health, prebiotics is where it's at in my opinion.