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Jul 20, 2023

Probiotics vs. Prebiotics: What’s the Difference?

By Tiffany Ayuda Medically reviewed by Kerri Glassner, DO Gut health is

By Tiffany Ayuda

Medically reviewed by Kerri Glassner, DO

Gut health is certainly having its moment in the wellness sphere. Just take one scroll through TikTok, and you’ll see all sorts of experts and influencers getting pretty comfy with convos around digestion. But if words like microbiome and flora still leave you scratching your head, the difference between probiotics and prebiotics is probably pretty confusing too.

It seems like these words are everywhere, and the buzz around them is affecting the way people are thinking about wellness. According to a 2022 food and health survey commissioned by the International Food Information Council1, 29% of Americans say they’re interested in improving their gut health, and 33% of them are looking to probiotic supplements to help them do so. Food manufacturers are taking note too, and have begun marketing products, from trail mix to fruit snacks, with a probiotic angle. Now prebiotics are starting to show up on store shelves as well, in everything from sparkling water to protein bars.

Probiotics, often described as "good" bacteria and yeasts that live in and on your body, have been at the heart of the gut health conversation: While researchers are still exploring the potential of these beneficial bugs, they’ve been lauded for promoting better digestive health to supporting your immune system. But they don't work alone, and that's where prebiotics—a term often confused with probiotics—come in. Like flowers in a garden, probiotics need to be fertilized to grow and survive. Prebiotics do just that: These plant fibers fuel the growth of probiotics in your gut and allow them to proliferate, creating a more diverse colony of gut bacteria, per the Mayo Clinic.

While probiotics and prebiotics work together, there are some important differences in how they may affect your body. But before we delve into that, it's helpful to take a step back to understand why all of this is important in the first place.

Your gut microbiome is home to trillions of microbes, including bacteria, fungi, viruses, and parasites, which primarily live in your digestive tract. It's a spectrum in there, Curtis Huttenhower, PhD, codirector of the Harvard Chan Microbiome in Public Health Center, tells SELF. On one end, there are microbes that support your health2. In the middle are some neutral bugs that don't really affect you much and on the other end, there are some microorganisms that can be harmful, especially if they start to thrive and make themselves at home3.

It's when you get a disruption or an imbalance in that normal makeup3 that things may get dicey. A shift in your gut microbiota3 can lead to something called dysbiosis4, and that can potentially cause the immune system to become hypersensitive in some people5. This can trigger some common GI symptoms like diarrhea, abdominal pain, and bloating, among others. (Of course, "normal" is super individualized, and what is healthy for one person may be different than what is for another.)

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That's why balance in your gut microbiome's composition is so important. A larger variety of microorganisms means your body is likely going to be better equipped to fight harmful pathogens6, Jessie Wong, RDN, a registered dietitian who specializes in digestive health and irritable bowel syndrome, tells SELF. As for what can help with that rebalancing? That's where probiotics have earned a lofty reputation3.

According to a consensus of an international expert panel gathered to nail down what the term probiotics really means, probiotics are "live microorganisms which, when administered in adequate amounts, confer a health benefit on the host."7 (Ahem, the "host" is you, by the way!)

When we talk about probiotics, we’re most often referring to dietary probiotics, or those naturally present in food sources. Strains of bacteria—such as Lactobacillus or Bifidobacterium8—are typically used in the fermentation of foods. Some good probiotic sources include:

When you eat fermented foods, the microbes enter your digestive system. They pass through your stomach, where most of them are killed. The microbes that survive make it to the small intestine, where some of them will pass through. Then they travel to the colon—an environment home to many different species of microbes. The microbes stick around there for some time, depending on your gut's structure and environment, says Wong.

Once there, the probiotics produce beneficial chemicals9 that support your immune system and inhibit the growth of bad microbes in the gut, Dr. Huttenhower says. They break down fiber (the prebiotics that we’ll talk about later), and the byproducts from that fermentation—which include short-chain fatty acids—help feed your intestinal cells and keep your intestinal barrier healthy, Wong says. That's important, since a properly functioning barrier serves as a line of defense that keeps harmful bacteria and substances out of your body10.

Along with dietary probiotics, there's also an emerging class of probiotics called live biotherapeutic probiotics (LBPs)11, Dr. Huttenhower says. These LBPs are in the early stages of development and are "specifically engineered to colonize the gut and be beneficial" to people with specific health conditions, such as inflammatory bowel disease (IBD), like Crohn's and ulcerative colitis, and Clostridioides difficile infection, he says.

Prebiotics are the nondigested plant fibers, or carbohydrates, from food that the gut ferments to produce beneficial chemicals.

When you consume fermentable fibers, research suggests that they feed beneficial microbes, helping increase and strengthen good guys12 such as Lactobacillus and Bifidobacterium, so that they occupy more surface area in your gut lining, Wong says.

"The goal of a prebiotic is to promote the growth of good bacteria that are already there," says Dr. Huttenhower. "Prebiotic fibers aren't absorbed in the stomach or small intestine, so when they reach the colon, microbes feed off them, which ultimately helps them grow." Ideally, this should make for a diverse and balanced gut microbiome12.

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The good news is that dietary prebiotics are commonly found in a whole bunch of fiber-rich foods:

To diversify your sources, try to incorporate different options throughout your meals, says Wong. For instance, rather than always eating rice as your dinner side, try to sub in quinoa or pasta some days, if you can, or mix up the type of fruits and vegetables you add to your smoothies. And if you always top your salad with tomatoes, maybe you cycle among bell peppers, roasted zucchini, or berries as well. Wong also suggests aiming to have a serving of fruit with each meal and trying two different types of veggies with lunch and dinner, if that's an option for you.

When you consume the right strains and in adequate amounts, probiotics can support the gut microbiome, says Wong. And prebiotics, as we’ve mentioned, also play a role in that balance. When your gut microbiome is thriving, this may help support immunity13, boost mood14, and even be protective against certain diseases in some people, says Wong. "Probiotics alone don't do it, but they do benefit our gut microbes, and improvement to our gut microbes is what is beneficial."

For instance, a balanced microbiome may help reduce inflammation in the gut, thanks to those short-chain fatty acids that are produced when probiotics break down prebiotic fibers. That's a big deal, since chronic inflammation has been linked to conditions like IBD, type 2 diabetes, and even anxiety and depression. In fact, the microbes in your gut actually produce serotonin, the neurotransmitter that plays a key role in brain function, mood, and cognition according to research in the journal Scientific Reports15.

We just don't know, though, whether probiotics (and the prebiotics that support them) can actually change the gut's composition over time. Because dietary probiotics don't colonize the gut, their potential effects are temporary. In fact, research shows that most of the microbes in your gut will be established before the age of three16.

What's more, the gut composition is a particularly tricky area to study because it all varies so much from person to person, Dr. Huttenhower says. So even if people are consuming the same probiotic- and prebiotic-rich foods, they can have different effects, making it difficult to generalize. Plus, even if you feed a bunch of people yogurt every day for 10 years, it's impossible to tease out whether the yogurt's probiotics were responsible for any noted effects, simply because there's a whole lot else going on during that time that can affect the gut.

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On the other hand, since LPBs, also known as smart probiotics, do colonize the gut and aren't transitory, they may offer more promise to treat chronic conditions, Dr. Huttenhower says.

Probiotic supplements claim to provide the same microbes used to ferment foods—most commonly in the Lactobacillus and Bifidobacterium families—but with a greater concentration than you’d get in a typical serving of, say, yogurt, says Dr. Huttenhower. Prebiotic supplements usually only include a small amount of one or two types of fermentable fibers, such as inulin, Wong says.

In general, when it comes to getting enough probiotics and prebiotics, food sources are going to be your best bet, says Wong. Taking different supplements without knowing what you actually need can mess with your gut, and potentially make symptoms worse or create new issues. What's more, you’d be missing out on all the other benefits you’d get from food, like vitamins, minerals, and other important micronutrients.

"In my clinic, I see a lot of people taking probiotics for mild constipation and bloating," says Wong. "But the probiotics they’re taking may not work for their specific system, and that can give them severe diarrhea, for example." Plus, taking in too many prebiotics from supplements—especially those containing inulin—may also worsen GI symptoms17, leading to potential side effects like bloating, cramping, and farting, especially for those with gut issues.

Then there's also the fact that dietary supplements don't require FDA approval. This means companies can make functional claims about a product—say, that it helps promote healthy digestion—without it being tested and verified as strictly as a drug would need to be. Finally, much of the research on probiotics is done on certain strains at certain amounts, so if the commercial supplement you’re using doesn't match up, the potential benefits likely won't, either18.

All this doesn't mean that supplements are necessarily a bad idea, though, especially if your doctor thinks one might be worth a try if you have a specific GI issue. You should talk with a gastroenterologist or a registered dietitian who specializes in digestive health to help determine which kind would be best for you.

Otherwise, if a healthy gut is top of mind, place your focus on food instead, says Wong. Diversify your diet with food sources rich in both the probiotics and prebiotics mentioned above for the most synergistic effect, she says. If you focus too much on one without the other, you’re probably missing out on their stronger-together combination.

Just think about an apple: It contains multiple types of fiber (prebiotics), and all of these different fibers travel to your colon to feed multiple strains of microbes (probiotics), helping a variety of them flourish. So if you repeat that process with a whole host of grains, fruits, and vegetables, you’ll not only fuel your body with nutritious eats, but your gut microbiome will likely thank you too.

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