Prebiotics: What Are They and How Can We Use Them Properly?

Introduction

Continued research on probiotic supplementation has led to the discovery of a myriad of health promoting benefits. However, these advantages are only possible if the probiotic microorganism can survive, colonize, and optimally function within the human intestinal tract. Prebiotics aid in these functions and select prebiotic sources may be more optimal for certain probiotic species. This review discusses the purpose of prebiotic supplementation and the enhancing effect of certain prebiotic sources on common probiotic microorganisms. 

Prebiotics 

The purpose of a probiotic does not terminate simply after delivery of viable bacteria to the gastrointestinal tract (discussed in “Choosing and Using: Factors to Consider for Probiotic Consumers”). Delivery is only the first step. After delivery, the bacteria must maintain viability for colonization, produce health-promoting products (discussed in “Postbiotics: The Interactive World Within and Beyond the Gut”) and, preferentially, proliferate. Prebiotics can promote these factors. Just as humans need food for growth, intestinal bacteria consume prebiotics for growth and improved function.^1,2 Prebiotics are classified based on the following criteria:^3,4  

• Resist digestion and absorption in the upper GI tract 

• Fermentable in the intestines with minimal to no fermentation in the mouth 

• Stimulates strain- or species-specific probiotic growth without stimulating pathogenic microorganisms

• Provides health benefits to the consumer 

Selecting prebiotics 

Generally, prebiotics are fermentable fibers specifically fermented by select microorganisms or bacteria.^3,5 Prebiotics are commonly found in food but can also be purchased and consumed as supplements. Studies have determined that oligosaccharides are the best prebiotic source. These include fructooligosaccharides (FOS), galactooligosaccharides (GOS), isomaltooligosaccharides (IMO), xylooligosaccharides (XOS), transgalactooligosaccharides (TOS), and soy oligosaccharides (SBOS).^3,6 Other prebiotics include lactulose, lactosucrose, and polysaccharides such as inulin, resistant starch, cellulose, and pectin.^3,7 An article from Cleveland Clinic claims that good prebiotic food sources include “legumes, garlic, asparagus, onions, leeks, certain artichokes, green bananas, and wheat.”⁵ Ranadheera et al. reviewed the specific prebiotics and their beneficial effects on select probiotic bacterial species in certain dairy products.² Table 1 summarizes pertinent findings. 

Note: Many prebiotic substances can be found in dairy products. Certain prebiotics may selectively enhance growth, viability, and functionality of probiotic bacterial species.

Recently, the development of synbiotics has grabbed the attention of food industries as well as probiotic researchers and consumers.⁷ A synbiotic is a product containing both a probiotic and a prebiotic.¹ Most commonly, Lactobacillus and Bifidobacterium species are combined with inulin.³ 

However, some argue that proper use of prebiotics, even without probiotic supplementation, is sufficient for host intestinal bacteria to provide adequate health benefits.^3,5 Markowiak et al. list the health promoting benefits of certain prebiotics alone on conditions such as type 2 diabetes, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), obesity, atopic dermatitis, and even adjunctive treatment for cancer side effects.³ However, these benefits can be further personalized by understanding the effect of prebiotic stimulation of postbiotic production. These metabolites are produced in the presence of probiotics and their prebiotic substrate. In the absence of prebiotics, probiotics rely on alternate sources of energy leading to production of undesirable and potentially harmful metabolites.⁸ The following paper titled, “Postbiotics: The Interactive World Within and Beyond the Gut” describes how select prebiotics stimulate select probiotics to produce desirable postbiotics.

Prebiotics have been found to serve additional purposes aside from probiotic enhancement. Interestingly, prebiotics have been used as a sugar replacement in certain foods such as yogurts, cakes, chocolates, soups, and sauces. Even the sensation of “mouth feel” has been improved by prebiotic application in baby foods, yogurts, and beverages.⁴

Side effects

Prebiotics are non-digestible. As such, osmotically induced diarrhea and fermentation induced flatulence with associated borborygmi (loud stomach grumbling) and stomach pain are potential side effects.^3,9 These side effects are mainly seen with excessive prebiotic consumption and/or prebiotic intake without probiotic intake.³ In fact, these effects are dose and time dependent. Usually, borborygmi and excessive flatulence occur first and, at increasing prebiotic doses, is followed by abdominal pain (cramps, bloating) and then diarrhea. These side effects also depend on individual host susceptibility. However, most individuals can tolerate a maximum of 20 grams of prebiotic substance per day.⁹ Hence, avoiding the side effects of prebiotics requires prebiotic moderation and timely probiotic intake. For more information on best probiotic supplement intake methods see “Choosing and Using: Factors to Consider for Probiotic Consumers.” 

Topical Prebiotics

Just as studies on the efficacy of prebiotic supplementation is limited, research on the use of topical prebiotics is even rarer. However, a recent study by Noll et al. considered the use of prebiotic and synbiotic baths and examined their effects on patients with atopic dermatitis (AD).¹⁰ Significant improvements were seen in all AD symptoms from taking a daily 10-minute prebiotic bath consisting of maltodextrin (2.88 g/L), inulin (6 g/L), and apple pectin (3 g/L). Improvements in redness, dryness, and pruritis were seen continuously up to the last day (day 14) of treatment. Alterations in the skin microbiome were also analyzed in both treatment groups. Specifically, the increased abundance of Micrococcus indicates a shift in favor of better skin health. 

Although synbiotic baths showed even more promising results, this study highlights the potential efficacy and need for further research on prebiotics alone as a topical treatment for AD and other skin conditions.

Key Takeaways

Prebiotics promote the beneficial health effects of probiotics both in the resident microbiota and when taken as a supplement. Prebiotics enhance the functionality of probiotics. Key points on the function of prebiotic supplementation are listed below.

1. Non-digestible fermentable fibers are the best prebiotic sources

2. Individuals can consume prebiotics that selectively optimize the species present in their probiotic product

3. Individuals may attain a healthy gut microbiome with proper prebiotic supplementation alone

4. Research on topical prebiotics is limited but further studies may offer more promising options for the treatment of skin specific conditions