If you’ve been keeping an eye on current research, you might think that the journey to whole-body health and wellness begins in your gut. This idea isn’t new: even Hippocrates said, over 2000 years ago, “All disease begins in the gut.” And as we learn more and more about the microbiome and its relationship to health and disease, this millenia-old statement certainly does seem true. In an effort to support gut — and therefore, whole-body — health, more and more people are turning to probiotics and prebiotics. But it can be confusing to know the difference between the two, whether you should take one or the other, or even if you can (or should) take both at the same time. In this article, we’ll simplify probiotics vs prebiotics so you’ll never have to ask again, “What’s the difference?”

What are probiotics?

We have an entire guide delving into "what are probiotics," but the World Health Organization (WHO) defines probiotics as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.” Most familiarly found in yogurt, probiotics have been around for a long time. However, they aren’t just found in yogurt, and they aren’t just for the gut.

• The most common probiotic bacteria are Bifidobacterium and Lactobacillus, which can be found in yogurt and other fermented dairy products. They can also be formulated into powder or pills.
• Fermented foods and beverages  — such as kimchi, kefir, kombucha, and others  — are another source of probiotic bacteria.
• Many probiotic species have been used to treat gut conditions such as antibiotic-associated diarrhea, inflammatory bowel disease (IBD), constipation, and more (for a full list of diseases treated with probiotics, read our article on probiotics).
• Probiotics can also help treat skin conditions (i.e., eczema) and respiratory tract conditions (i.e., asthma and viral infections such as COVID-19).

Probiotics aren’t for everyone though. They can worsen symptoms or cause serious side effects in people with:

• Compromised immune systems
• Certain gut disorders, such as small intestinal bacterial overgrowth (SIBO)
• Other chronic diseases

And, while they’re great for treating some diseases, probiotics really don’t do much for people who are already healthy.

What are prebiotics?

Again, we have an in-depth guide on "what are prebiotics" here, but if probiotics are the living organisms, then prebiotics are the food for those living organisms. Prebiotics are a specific group of fibers (non-digestible carbohydrates) — found in vegetables, fruits, and whole grains — that:

• Are not digestible by mammals
• Are fermented (digested) by microbes
• Improve activity and viability of beneficial microbes

Like probiotics, prebiotics can also be isolated (from foods) and made into supplements.

Microbes that ferment fiber produce short chain fatty acids (SCFAs) and other bioactives that regulate metabolic and immune pathways. SCFAs are molecules with a wide range of health benefits for humans, including:

• Lowered risk of diseases (e.g., colorectal cancer)
• Lowered intestinal inflammation
• Better regulated blood sugar
• Improved absorption of vitamins and minerals
• Increased satiety and reduced hunger

Similar to probiotics, prebiotics can make symptoms worse in people with specific gut disorders, most notably irritable bowel syndrome (IBS). But because they are non-living, they don’t pose the immune dangers that prebiotics can for immunocompromised individuals.

Because of all of the health benefits associated with eating prebiotic fibers and their relative safety, leading medical providers advise consumption of prebiotics over probiotics for supporting general health and well-being. If you’ve heard otherwise, it may be because some research suggests that we’ve lost our natural beneficial bacteria over the years as we’ve evolved to eat a high-fat, refined carbohydrate diet. For this reason, some believe that simply eating prebiotics won’t really help: if the bacteria that ferment prebiotics aren’t in your gut to begin with, then the prebiotics cannot exert a positive effect. But, a lot of different bacteria can ferment fiber, so losing one or two types isn’t likely to make a difference. Supporting this, numerous reputable research studies show that most humans do have plenty of fiber-fermenting bacteria in their guts. 

Probiotics vs. prebiotics: Can (and should) you take both?

So, if probiotics can help treat disease, and prebiotics feed probiotics (and thus might enhance the latter’s efficacy), the question naturally follows: Shouldn’t you just take both? The answer really depends on why you’re taking them:

• If you have a specific condition that can be helped with probiotics, your doctor might recommend one for you.
• If you are taking a probiotic to treat a disease, your doctor might also give you a prebiotic supplement to support and enhance the probiotic.
• If you are healthy, but seek to maintain general health and well-being, the best approach is to eat a diet rich in prebiotic fibers. 

Many commercially available supplements (which, importantly, have not undergone the rigorous testing required to be FDA-approved as a drug or medicine) are a mixture of prebiotics and the probiotic bacteria that eat them. You could select such a product, but buyer beware: We don’t really know yet whether such mixtures are more beneficial than just eating a fiber-rich diet.

Key takeaways

Probiotics are living microorganisms that can have a positive impact on health, while prebiotics are nutrients for the microorganisms in your gut. The research to date is pretty clear: Probiotics demonstrate some efficacy in treating specific conditions, but not for supporting health in generally healthy individuals. On the other hand, prebiotics — particularly when derived from fibrous foods — measurably and significantly support general health and well-being. While taking both at the same time could enhance a probiotic’s ability to treat certain conditions, such an approach is something best left to your doctor to decide.