Prebiotics vs. Probiotics: What’s the Difference?

If you’re well-versed in the wellness world, you’ve undoubtedly learned about the gut microbiome and tried incorporating probiotics or fermented foods into your diet.

You think you know all there is to know about gut health, and then along come prebiotics.

At first, you think people are just making a typo when they try to write “probiotics,” but you finally realize that prebiotics are their own separate entity that you need to learn all about.

Not to worry; we’ve got you covered in this article, where we’ll detail everything you need to know about the difference between prebiotics and probiotics and where to find them—oh, and we’ll throw in some information about postbiotics and synbiotics, too (yep, there’s more!).

What Are Prebiotics?

The simplest way to describe prebiotics is that they are the fuel our healthy gut bacteria consume. 

For a technical definition, prebiotics are described as “nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and activity of bacteria in the colon, thus improving host health.”

To break that down, prebiotics are types of dietary fiber that are not digested or absorbed by our digestive systems.

Rather, they are consumed and fermented by various microbes in the colon (large intestine). When colonic bacteria consume prebiotic fibers, these microbes can grow and thrive in the gut, which benefits the host (us!).  

Various gut bacteria use carbohydrate-hydrolyzing enzymes to break down and ferment prebiotic fibers, producing hydrogen, methane, carbon dioxide, lactate, and short-chain fatty acids.

In turn, these fermentation byproducts (also known as metabolites) provide energy for certain gut microbes to use, allowing them to continue living and growing in the colon.

Primarily, the breakdown of prebiotic fibers stimulates the growth of Bifidobacterium, a good bacteria genus known to improve gut health. 

While prebiotic supplements exist, these fibers are also found in many plant foods, including leeks, asparagus, chicory, less-ripe bananas, Jerusalem artichokes, garlic, onions, wheat, oats, and beans.

The types of prebiotic compounds found in these foods include resistant starch, pectins, gums, non-digestible oligosaccharides, and sugar alcohols.

In supplement form, you may see prebiotics on labels as galactooligosaccharides (GOS), transgalactooligosaccharides (TOS), polydextrose, wheat dextrin, acacia gum, psyllium, potato starch, glucomannan, or inulin.

Benefits of Prebiotics

Short-Chain Fatty Acids

Short-chain fatty acids (SCFAs) are beneficial fermentation byproducts known as metabolites that are produced when our gut bacteria feed on prebiotic fibers.

The three primary SCFAs are acetate, propionate, and butyrate, with butyrate providing the most benefits.

Our colonic epithelial cells (the thin layer of cells making up our gut lining) prefer to use butyrate as a fuel source (even more than glucose).

Butyrate is an essential nutrient that helps colonocytes (colon cells) grow and thrive, promoting normal cell growth and strengthening the intestinal barrier.

Therefore, having enough available butyrate (which comes from eating prebiotic fibers) may be a critical factor in protecting against colonic disorders. 

SCFAs lower pH in the gut, limiting the growth of harmful bacteria that cannot survive in lower-pH environments. SCFAs can also enhance the absorption of calcium and other minerals. 

The other SCFAs are also important. Acetate is used by our brains, muscles, and tissues, and studies suggest that it benefits energy metabolism and is linked to appetite control and healthy body weight.  The third SCFA, propionate, is metabolized and used by the liver, where it can interfere with cholesterol production and lead to healthier blood cholesterol levels. This may be one reason why high-fiber diets are known to lower cholesterol levels and support heart health.

Digestive Health

It’s well-known that dietary fiber is beneficial for digestive function, and prebiotic fiber is no exception. 

Prebiotics may be particularly helpful for improving constipation, as seen in a 2020 review that found inulin fiber to increase the frequency of bowel movements and improve stool consistency in people with irritable bowel syndrome.

The researchers also concluded that inulin fiber increased intestinal transit time (the time it takes for food to move through the digestive tract) in people with constipation.

Consumption of prebiotic fiber has been shown to reduce the prevalence and duration of infectious and antibiotic-associated diarrhea, improve symptoms related to inflammatory bowel disease, and reduce the risk of colon cancer. 

However, the devil is in the dosage when it comes to prebiotics. High amounts of dietary fiber in any form can cause painful digestive symptoms in many people, especially IBS sufferers.

The exact dose and type of prebiotics that improve digestive health are not yet known. However, consuming prebiotics in food (rather than supplements with higher doses) may be preferred for people with IBS or other digestive disorders because foods typically have smaller amounts of prebiotics than supplements.

Weight and Metabolic Health

Because fiber is not digested, it is highly satiating—meaning it keeps us fuller for longer. The satiety factor and the correction of gut dysbiosis are two potential reasons why prebiotics are linked to weight loss. 

One small study with 48 overweight adults found that taking 21 grams of fructooligosaccharide prebiotics for 12 weeks led to significant weight loss compared to a control group.

The weight loss wasn’t much—the prebiotics group lost an average of 1.03kg (2.23 lbs)—but it was better than the control group that gained weight over the study.

Brain Health

Increasing evidence suggests that neurodegenerative disorders like Alzheimer’s and Parkinson’s disease are, in part, modulated by SCFA activity.

Although there is no available research in humans, studies with animals have shown that giving a form of butyrate improved memory in mice with advanced stages of Alzheimer’s disease. 

Researchers speculate that SCFAs like butyrate benefit the brain and central nervous system by influencing neurotrophic factors like BDNF (brain-derived neurotrophic factor), which helps facilitate neurogenesis—the growth and maintenance of new neurons. SCFAs also play a role in neurotransmitter communication and help to maintain the integrity of the blood-brain barrier.

What Are Probiotics?

With their name rooted in the words “for life,” probiotics are live microorganisms that can benefit the host they live in—which, in this case, is us. 

Our guts contain trillions of bacteria—helpful, harmful, and neutral bugs—that constantly compete for space. Therefore, adding probiotics to your diet or supplement regimen can help crowd out the pathogenic gut bacteria and allow beneficial bugs to take hold. 

Although the term “gut microbiome” is commonplace today, it wasn’t coined until 2001, when researchers started realizing just how important the collection of intestinal microbes is to our health. 

When our gut microbiota populations become out of whack, dysbiosis—an imbalance of good and bad bacteria—can develop. Dysbiosis can also include low microbial diversity.

Microbial diversity is essential because various bacterial species do different things, ranging from digesting fiber to producing vitamins and metabolites to modulating immune system function. 

Dysbiosis is a common cause of health problems—both digestive and non-digestive—so repopulating your gut microbiome with friendly bacteria can help to correct this imbalance. 

In our diets, probiotic-rich foods are all fermented foods, including yogurt, sauerkraut, kefir, pickled and fermented vegetables, kimchi, natto, miso, tempeh, and more.

Health Benefits of Probiotics

Probiotics have many potential benefits to human health, both digestive and non-digestive—let’s take a closer look.

Digestive Health

Probiotics have been studied most for their benefits to digestion and gut health.

One key reason behind this is probiotics’ role in managing dysbiosis. When our gut microbiota populations become out of whack, dysbiosis—that imbalance of bad and good bacteria—can develop.

Probiotics are also thought to improve several health conditions or symptoms related to digestion, including:

• Constipation
• Diarrhea, including acute infectious diarrhea, antibiotic-associated diarrhea, and Clostridium difficile-associated diarrhea)
• SIBO (small intestinal bacterial overgrowth)
• Irritable bowel syndrome (IBS) symptoms
• H. pylori infection, which causes gastric ulcers and gastritis
• Inflammatory bowel disease (IBD), which includes ulcerative colitis and Crohn’s disease

However, the research is mixed when it comes to Crohn’s disease, and probiotics may only promote digestive health in people with ulcerative colitis.

Mental Health

Although the gut-brain axis is a recently coined term, people have known that digestion and emotions are linked for hundreds of years. 

Probiotic bacteria thought to benefit neurological or psychological symptoms are called “psychobiotics,” as they act on neurotransmitters and other areas of the central nervous system. 

Scientific evidence shows that probiotic supplements may benefit mental health disorders.One meta-analysis of 34 clinical trials concluded that taking probiotics led to small but significant effects in reducing symptoms of depression and anxiety.

Heart Health and Metabolism

Most people have heard of the gut-brain axis now—but the gut-heart axis is an even newer area of research. 

The gut-heart axis involves how the bacteria and metabolites in our digestive tracts influence our cardiovascular system. 

The microbiomes of people with heart disease or other cardiovascular conditions have been found to be different than those of healthy people, including alterations in gut bacteria species and metabolites like SCFAs. 

Gut dysbiosis is associated with adverse changes in lipid or cholesterol profiles that increase the risk of heart disease, including higher LDL cholesterol, lower HDL cholesterol, and higher blood pressure. 

This may be mediated by SCFA activity, as these gut metabolites influence blood pressure, blood sugar control, cholesterol, and lipid metabolism. 

This is one reason why taking prebiotics with probiotics is so beneficial, as prebiotics provide the fuel for microbes to produce SCFAs. 

Research suggests that certain probiotics can also help with weight loss or fat loss.

A meta-analysis of 23 clinical trials found that probiotics effectively reduced BMI (Body Mass Index), body weight, visceral abdominal fat, waist circumference, and hip circumference in 14 of the studies. 

Immune System Health

Probiotics can interact with several immune cells, influencing their activity and affecting immune function.

Studies have shown that probiotics can modulate innate and adaptive immunity in older adults and reduce the length of infection in children and adults. 

Research has also uncovered that taking probiotics can improve immune responses to influenza vaccinations, increasing protection from the flu.

For example, one meta-analysis found that people taking probiotics before getting the H1N1 influenza B vaccine had 53% protection rates against that virus compared to 37% in the group not taking probiotics. 

Other Conditions

Although the research is more limited here, probiotics may also help improve:

• Autoimmune conditions (multiple sclerosis, ulcerative colitis, lupus, rheumatoid arthritis)
• Inflammatory skin conditions (psoriasis, rosacea, eczema/atopic dermatitis, and acne)
• Allergies
• Leaky gut (also known as intestinal permeability)
• Oral health (cavities, periodontal disease, gingivitis)

Synbiotics 101

Okay, one more word to add to the mix is “synbiotic.” As the root “syn” means “with” or “together,” synbiotics refers to supplements that combine prebiotics with probiotics. 

Synbiotics can be beneficial because prebiotics are an energy source for probiotics. So, taking a synbiotic can help to maximize the synergistic effects of probiotics and prebiotics.

They can be particularly helpful if you don’t eat a high-fiber diet. In this case, choosing a synbiotic supplement instead of just a probiotic supplement can ensure that the beneficial gut bacteria have enough fuel to consume and can survive and thrive in your gut. 

For more details about supplements, check out our full articles and mini-reviews on the Best Probiotics for Men, Best Probiotics for Women, and Best Prebiotics for Gut Health.

Some of our favorite synbiotic supplements that combine probiotics and prebiotics include:

• Garden of Life Dr. Formulated Once Daily Probiotic: This probiotic supplement has 50 billion CFUs of helpful bacteria made up of 16 probiotics, including Lactobacillus reuteri and Lactobacillus fermentum, and prebiotic fibers like organic acacia fiber and potato starch. 
• WiseHuman Women’s Daily Probiotic: With 20 billion CFUs (colony-forming units) of probiotics and prebiotics, this supplement is designed to support digestive, vaginal, and immune system health. 
• Nordic Naturals Flora Probiotic Daily: This supplement contains 12 billion CFUs of live bacteria, including the first commercialized probiotic for dietary supplements, Lactobacillus acidophilus DDS-1, combined with the prebiotic fiber FOS (fructooligosaccharide) to support healthy gut bacteria growth.

Prebiotics and Probiotics FAQs