We might like to think of our gut microbiome as an immobile, somewhat mysterious presence in our gastrointestinal tract. But in reality, these organisms are active, living things—and all living things need food to function.

We’ve talked about the beneficial gut bacteria we call probiotics in another Gut Check article, and now it’s time to focus on a very important question: What feeds these organisms? The answer is prebiotics.

What Makes Something Prebiotic?

If this is your first time hearing extensively about prebiotics, you’re not alone. Our 2018 Food & Health Survey indicates that many people are unfamiliar with the health benefits of these compounds: Only 36 percent of people said they were healthy compared to 62 percent who said the same for probiotics. A whopping 35 percent were unaware of their effect on health.

It’s easy to confuse probiotics and prebiotics or assume that they’re the same thing—after all, they differ by only one letter. But if you have one takeaway from this article, make sure it’s that probiotics are the bacteria that are beneficial for our health, and prebiotics are what feed probiotics.

The technical definition of prebiotics is “a substrate that is selectively utilized by host microorganisms conferring a health benefit.” In simpler terms, we can think of them as carbohydrates that cannot be degraded by human digestive enzymes. Instead, prebiotics travel to our lower gastrointestinal tract where they’re fermented by probiotic bacteria.

This results in the production of short-chain fatty acids, which are thought to have a number of beneficial health effects, including reducing risk for certain types of cancer, enhancing calcium absorption, improving bowel function and providing fuel for the cells that line our lower gastrointestinal tract, which maintains a healthy gut barrier against harmful bacteria and other substances that may cause illness.

Are prebiotics and dietary fiber the same thing?

The definition of a prebiotic might sound a lot like a description of dietary fiber. However, we need to draw an important distinction here. In order for a dietary fiber to be listed as such on a Nutrition Facts label, there needs to be evidence that it confers a benefit to human health.

However, these benefits don’t necessarily need to be mediated by probiotic bacteria—fiber can do the work itself. In comparison, prebiotics exert their health benefits through fermentation by microorganisms that have been specifically defined as probiotic, such as Lactobacillus and Bifidobacterium. In other words, all prebiotics are dietary fibers, but not all dietary fibers are prebiotic.

Which foods are sources of prebiotics?

Fruit, vegetables, cereals and other edible plants all have potential to provide prebiotics. Artichokes, asparagus, bananas, berries, chicory, garlic, green vegetables, legumes (like peas and beans), onions, tomatoes, oats, barley and wheat are among the sources of naturally occurring prebiotic fiber.

If you’re a food label reader, you might have noticed a few items on the ingredients list like lactulose, inulin and oligosaccharides, which are also classified as prebiotic. They are sometimes called “isolated” or “synthetic” fibers because they’re added to foods like granola bars, cereal, and yogurt to boost their nutrition content and aren’t intrinsically present in the original product.

Unfortunately, it’s well-known that most people don’t eat enough fiber: The average American eats about 16 grams per day, while the recommendation is 25 to 38 grams per day. This means that there’s definitely room to grow when it comes to bumping up our prebiotic intake.

As we continue to learn more about how our gut health affects our overall well-being, it’s clear that prebiotics and probiotics are important players in the game. It’s also evident that much more research is needed.

At this point, we don’t know what the “ideal” amount of daily prebiotic intake is, and there’s no map of exactly which strains of probiotic bacteria use which kinds of prebiotics, whether they are from an apple, an artichoke or inulin in a snack food. This makes it difficult to selectively enhance the presence of different types of beneficial bacteria, which may turn out to be an important factor for our health.

While we wait for more answers, it won’t hurt to get a jump-start on bumping up your prebiotic intake. Doing so might pack a one-two nutritional punch, since prebiotics are found in foods that are healthy for a variety of reasons in addition to their fiber content. As if we needed another reason to advocate for eating more fruits, vegetables and grains!