Prebiotics vs. probiotics

Prebiotics are not to be confused with probiotics. Probiotics make up the “good” bacteria (such as bifidobacteria and lactobacilli) that normally colonize in your colon and can be found in fermented foods like kimchi, sauerkraut, and yogurt. Prebiotics, on the other hand, are a type of soluble fiber only your gut can digest. The fiber passes through the upper portion of your gastrointestinal tract undigested, and serves as nourishment for the healthy bacteria in your colon. Think of it this way: Prebiotics feed probiotics.

Why you need them:

You want prebiotic foods in your diet because boosting probiotic groups like bifidobacteria can help reduce the amount of potentially damaging bacteria in your colon by improving your gut’s pH (it’s less hospitable for “bad” bacteria), help make your bowel movements more frequent, and actually boost your immune function. As probiotic bacteria thrive, they release beneficial digestive byproducts called short-chain fatty acids—the benefits of which range from preventing colon cancer to inducing remission in people with inflammatory bowel diseases.

Naturally, certain things we'd rather not deal with—like stress, a not-so-stellar diet, and antibiotics—can deplete our source of healthy gut bacteria, so you want to make sure you're taking care of the good stuff regularly. That’s not to say you should go on an all-out prebiotic frenzy; you’ll experience some not-so-nice side effects—gas, for one.

How prebiotics work:

When looking for prebiotic foods, you’re essentially looking for foods with fermentable fibers, such as oligosaccharides, galactooligosaccharide, and inulin, since they can increase the population of bifidobacteria.

What defines a prebiotic food

1. Prebiotic foods can be fermented by the microbes inside your colon.
2. They can stimulate the beneficial bacteria in your gut.
3. The food must be resistant to stomach acid and other digestive processes so it can make it to your intestines.

Click through to get the lowdown on the foods that prove it's what's on the inside that counts.