Prebiotics vs. Probiotics: What’s the Difference?

Over the past few years, the gut—and the trillions of bacteria inside it—has been getting a ton of buzz. Scientists are still learning exactly how and why gut bacteria play a role in our health, but they do know the gut’s bacterial makeup affects us far more than previously thought. Aside from improved digestion, having an abundance and a vast variety of good gut bacteria has been tied to reduced bowel inflammation, better regulated blood-sugar levels, lower cholesterol levels, and even improved mood. They’re also continuing to research the gut’s effects on everything from colon cancer to Alzheimer’s risk, and their findings are promising. Maybe that’s why sales of probiotic supplements have skyrocketed, and probiotic-fortified foods have become commonplace on supermarket shelves. These days, you can even send a stool sample to a team of scientists to get a personalized gut bacteria evaluation.

But here’s the thing most people don’t know: To reap these benefits, you also have to consume prebiotics, a type of dietary fiber on which probiotics feed. Here’s everything you need to know about this oft-overlooked nutrient.

Probiotics are the health-promoting gut bacteria you’ve been hearing about for years. They’re found in fermented food products like yogurt, sauerkraut, kimchi, and kombucha, and many types of probiotics are similar to the bacteria naturally residing in our guts. Probiotics swing your overall bacterial balance toward “good,” preventing harmful bacteria from overpowering your system and creating issues like inflammation, infection, or gastrointestinal symptoms linked to diarrhea and irritable bowel syndrome.

Prebiotics, on the other hand, are entirely different. Unlike probiotics, they’re not living organisms. Prebiotics are soluble, fermentable fibers that we’re unable to digest in our stomachs. This allows them to progress to our intestines, where they get gobbled up by probiotics and fermented into short-chain fatty acids. It’s these fatty acids that provide all the good-for-you benefits that keep us healthy long after we’ve eaten our last spoonful of Greek yogurt.

And yes, feeding our gut bugs really is vital: Without proper fuel, good gut bacteria can die off—or even turn on you. “Most bacteria are opportunists,” says Purna Kashyap, a gastroenterologist at the Mayo Clinic and member of the scientific advisory board for the American Gastroenterological Association Center for Gut Microbiome Research and Education. “They’ll try to find nutrients elsewhere—and could go after the mucus lining of your intestine.” That mucus is what protects your gut from nearby “bad” bacteria—so having less of it could put you at greater risk for infection or inflammation, according to research.

Adding prebiotics and probiotics to your diet

Getty Images

Prebiotics and probiotics are both essential to your health, that much is clear. But it’s not exactly obvious how one should go about consuming both nutrients. Consider this your cheat sheet:

When it comes to probiotics, naturally occurring sources always trump supplements, says Kashyap. There are a few reasons for this. First, while the good bacteria in foods like yogurt, kimchi, and kefir are sitting in a container waiting to become your lunch, they’re feeding on the carbohydrates and sugars that surround them. This ensures that they’re alive and well, and ready to boost your health after you've consumed them. The bacteria in supplements don't typically have anything to feed on so many of them will die off before you even pop the first one from the bottle into your mouth.

Natural sources of probiotics also have a greater variety of bacteria than supplements, which Kashyap says is crucial for gut health. “There is strength in number of microbes,” he says, “but there is also strength in diversity, which creates a more robust bacterial ecosystem. That way, different bacteria can easily feed on different nutrients in your system.” In fact, Kashyap says research shows that one common denominator for a variety of medical conditions, including diabetes and inflammatory bowel disease, is a low level of microbial diversity.

Like probiotics, prebiotics should be consumed through food, rather than a supplement. Thanks to their high soluble fiber content, Jerusalem artichokes (AKA sunchokes), chicory root, onion, garlic, and beans are all good sources, as are sources of resistant starch, a fiber that gets its name because it “resists” digestion in the stomach. Resistant starch resides in oats, unripe (green) bananas, and legumes—and because of the ways that starch is affected by heat, it’s also present in cooked then cooled pasta, potatoes, and rice. Since these prebiotic foods are likely part of your diet already, you can easily do your gut bacteria a service by whipping up a healthy potato or pasta salad, or spooning cold, cooked rice over a bed of greens, veggies, and grilled chicken.

A Part of Hearst Digital Media
Runner's World participates in various affiliate marketing programs, which means we may get paid commissions on editorially chosen products purchased through our links to retailer sites.