What Are Prebiotics? Prebiotics Benefits, Foods, and Downsides - Healthline

Many people are familiar with probiotics, the live microorganisms known to improve gut health. Probiotics are naturally found in some foods like yogurt, sauerkraut, and kimchi and are also commonly taken in supplement form to help support the digestive system.

But what about prebiotics?

Even though prebiotics affect the health of your digestive system — as well as many other parts of the body — these nutrients are often overlooked.

This article tells you everything you need to know about prebiotics, including what they are, how they affect your health, and how to take prebiotic supplements.

"Gut microbiota" refers to the trillions of microorganisms that live in your gastrointestinal (GI) tract and make up your gut microbiome. Your large intestine is home to the majority of these microorganisms (1).

They carry out functions that are essential to overall health, including nutrient metabolism and regulation of the immune system (2).

Your gut microbiota can even influence disease risk, including the risk of developing colon cancer, inflammatory bowel disease, and type 2 diabetes (3).

Diet and lifestyle factors significantly impact the diversity and types of microorganisms that live in the GI tract (2).

Prebiotics are essential to a healthy microbiome. In simple terms, they're nutrients that get broken down by gut bacteria.

Bacteria in the large intestine ferment prebiotics. This releases byproducts called short-chain fatty acids. These byproducts act as energy sources for the cells lining the colon, called colonocytes, and benefit health in many other ways (1).

Prebiotics also influence the makeup and function of gut bacteria, promoting the growth of beneficial microbes.

According to the International Scientific Association of Probiotics and Prebiotics, in order for a compound to be classified as a prebiotic, it should (1):

• resist stomach acid and digestive enzymes, plus should not be absorbed in the GI tract
• be able to be fermented by intestinal microbes
• stimulate the growth or activity of intestinal bacteria to improve health

There are many different types of prebiotics, including (1):

• fructans
• galacto-oligosaccharides
• starch- and glucose-derived oligosaccharides
• pectic oligosaccharide
• non-carbohydrate oligosaccharides

Most prebiotics are considered carbohydrates. However, some prebiotics are not classified as carbohydrates. Cocoa flavonols are an example of non-carbohydrate oligosaccharides.

Although prebiotics are often confused with probiotics, they are not the same. Probiotics are live microorganisms found in your gut, certain foods, and supplements that benefit health when taken in certain amounts.

On the other hand, prebiotics are nutrients that are dietary compounds that stimulate the growth and activity of certain microorganisms (4).

Some experts have referred to prebiotics as "microbiome fertilizers" (5).

Read more about the differences between prebiotics and probiotics here.

Where do you find prebiotics?

Prebiotics exist naturally in some foods, including (1, 6):

• asparagus
• Jerusalem artichoke
• onions and leeks
• tomatoes
• garlic
• oats
• honey
• bananas
• wheat, barley, and rye
• peas
• beans
• chia seeds
• cow's milk
• seaweed
• chicory
• dandelion greens

There aren't a lot of foods that naturally contain prebiotics. Plus, many foods that are high in prebiotics, such as artichokes and beans, aren't a regular part of many folks' diets.

For this reason, synthetic prebiotics are added to some foods to improve their nutritional content and health value. Prebiotics are also made into dietary supplements like powders and capsules.

Prebiotic supplements are used to treat specific health conditions and to improve overall gut health.

Some studies have shown that supplementing your diet with prebiotics may benefit people with gut-related conditions, high blood sugar, and more (7, 8).

However, compared with probiotics, research investigating the health effects of prebiotic supplements is much more limited.

Summary

Prebiotics are essential to a healthy microbiome. Prebiotics act as a fertilizer to the microbiome, as they stimulate the growth and activity of certain microorganisms.

A diet rich in prebiotics promotes digestive system health by stimulating the growth of beneficial microorganisms.

The fermentation of prebiotics produces short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate. They play important roles in gut and metabolic health.

For example, SCFAs provide energy for colonocytes and are involved in mucus production, regulation of intestinal pH, and more.

In addition to gut health, prebiotics influence immune function, blood sugar regulation, appetite, and energy expenditure (9, 10).

Studies suggest that when taken in specific amounts, prebiotics may improve health in various ways.

May improve certain gut conditions

Because prebiotics stimulate the growth of beneficial bacteria and improve certain aspects of gut health, they may benefit those who have gut-related health conditions like constipation.

A 2020 review noted that treatment with inulin, a type of prebiotic, may benefit folks who have irritable bowel syndrome (IBS) with constipation (11).

It may improve the frequency and consistency of stool as well as intestinal transit time, or the time it takes food to move through the digestive tract (11).

However, a 2021 review found limited evidence that treatment with prebiotics — or prebiotics mixed with probiotics (synbiotics) — is helpful for treating IBS and that the quality of existing studies is low (12).

So, most experts, including the American College of Gastroenterology, don't recommend prebiotics as a treatment for IBS.

Another 2020 review that included 21 randomized controlled trials found that prebiotic treatments were effective for improving stool consistency, number of bowel movements, and bloating in people with chronic constipation.

However, the researchers noted that it's still unclear which prebiotic formulation is best for treating constipation (13).

Even though more research is needed to assess the effectiveness of prebiotic supplements on constipation and IBS, consuming a diet rich in foods high in prebiotics supports overall gut health and may help stimulate the growth of beneficial microorganisms.

May improve metabolic health

Eating a diet rich in prebiotics and taking prebiotic supplements may benefit certain aspects of metabolic health, including blood sugar, cholesterol, and triglyceride levels.

A 2019 review of 33 studies found that treatment with the prebiotics called Inulin-type fructans (ITF) significantly reduced fasting blood sugar, a long-term blood sugar control marker called glycosylated hemoglobin (HbA1c), and fasting insulin levels (14).

The researchers found that these results were most significant in people with prediabetes and type 2 diabetes and recommended that people with these conditions supplement with 10 grams of ITF per day for 6 weeks and longer to reap these potential benefits (14).

Additionally, a 2021 review of 33 randomized controlled human trials found that ITF supplements significantly reduced levels of blood sugar, total cholesterol, and triglycerides in people with prediabetes and diabetes (15).

However, not all studies of prebiotics in these populations have found benefits.

A small 2021 randomized, double-blind crossover trial including 29 people with type 2 diabetes found that treatment with 16 grams of ITF daily for 6 weeks had no effect on fasting or post-meal blood sugar levels compared with a control treatment (16).

While prebiotic supplements may help improve certain aspects of metabolic health in people with prediabetes and type 2 diabetes, more research is needed to confirm these potential benefits.

Other potential benefits

In addition to having possible benefits for metabolic health and the potential to improve certain digestive conditions, prebiotics may benefit health in the following ways.

• May reduce markers of inflammation. A 2017 review found that 14 out of the 29 included prebiotic studies reported a significant decrease in 1 or more markers of systemic inflammation. SCFAs may help reduce inflammation by maintaining the health of the intestinal lining and preventing the movement of pro-inflammatory molecules across the gut wall (17, 18).
• May reduce appetite and cravings. Some studies have found that supplementing with prebiotics like galacto-oligosaccharides and oligofructose-enriched inulin may reduce appetite and cravings for specific foods, like sugary foods (19, 20).
• May help reduce body fat. A 2021 review that included 27 studies concluded that synbiotics, or the combination of probiotics and prebiotics, may aid in weight loss and fat loss in people with overweight or obesity (21).

Keep in mind that this list is not exhaustive, and there are many other potential benefits related to prebiotics.

Clinical trials exploring the effects of prebiotic supplements on knee osteoarthritis, obesity, allergies, multiple sclerosis, type 1 diabetes, atopic dermatitis, and more are currently underway (22, 23).

Summary

Prebiotics may help improve constipation, blood sugar levels, inflammatory markers, and more. However, more research is needed to confirm these potential benefits.

Most types of prebiotics are considered safe and aren't associated with serious side effects (24).

Prebiotics are even considered safe during pregnancy and lactation (25).

However, because prebiotics are fermented in the large intestine, taking large doses may lead to symptoms like gas, cramps, diarrhea, and bloating.

The likelihood of a prebiotic causing the side effects listed above depends on several factors.

Prebiotics with a shorter molecular structure or chain length, such as inulin, are more rapidly fermented in the first part of the colon, while prebiotics with longer chain lengths are fermented at a slower rate in the latter part of the colon.

So, shorter-chain prebiotics are more likely to cause GI side effects (24).

What's more, larger doses of prebiotics are more likely to cause certain side effects than smaller doses.

While low doses of 2.5–10 grams per day can lead to mild symptoms like gas, high doses of 40–50 grams per day could cause diarrhea (24).

It's important to note that a daily dose of 2.5–10 grams of prebiotics is necessary in order to reap their health benefits. That means prebiotics may cause side effects, even at recommended therapeutic doses (1).

Although prebiotics haven't been associated with dangerous side effects, it doesn't mean they're the right choice for everyone. While some people may have no side effects after they take prebiotics, some may experience significant bloating and GI discomfort.

If you're interested in taking prebiotics, it's best to get advice from a knowledgeable healthcare professional first. They can help you decide whether prebiotics are appropriate for your health needs.

Summary

Prebiotics are considered safe but may cause GI side effects in some people, including bloating, cramping, and diarrhea.

Experts suggest that if you want to take prebiotics, a daily dose of 2.5–10 grams is the minimum required for a meaningful effect on your health.

The majority of prebiotic supplements on the market contain between 1.5–5 grams of prebiotics per serving (1).

Most prebiotic supplement manufacturers recommend taking a serving of prebiotics one or more times per day with a food or beverage.

Prebiotic powders can be mixed with beverages like water or smoothies.

They can also be added to foods like yogurt.

Keep in mind that some prebiotics have special instructions for use.

For example, psyllium husk, a fiber with prebiotic properties, should be taken with plenty of fluids, as it has a bulking effect on stools. It can lead to constipation and even intestinal or esophageal obstruction if it's not taken with adequate fluids (26).

If you're trying out a new prebiotic supplement, it's important to read instructions and use the prebiotic as recommended to avoid potential side effects.

Also, it's suggested to start with a smaller dose of prebiotics and slowly increase the amount over time in order to minimize digestive side effects.

Summary

The majority of prebiotic supplements on the market contain between 1.5–5 grams of prebiotics per serving. They can be taken with food or beverages. Be sure to follow the supplement instructions to avoid potential side effects.

Prebiotics are sometimes referred to as microbiome fertilizers.

They promote the growth of beneficial microbes, fuel colonocytes, and influence health in many other ways.

Some evidence suggests that prebiotic supplements may be helpful for those with chronic constipation, prediabetes, type 2 diabetes, and more — but more research is needed.

If you're interested in taking a prebiotic supplement, talk with a healthcare professional first. They can help you decide whether a prebiotic supplement is right for you.

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