What are prebiotics?
Prebiotics were first defined in 1995 as non-digestible food ingredients that selectively stimulate the growth or activity of beneficial gut bacteria. Over the years, scientific advancements have refined this definition. In 2017, the International Scientific Association for Probiotics and Prebiotics (ISAPP) redefined prebiotics as “a substrate that is selectively utilized by host microorganisms conferring a health benefit.” This updated definition expanded the scope of prebiotics beyond carbohydrates, recognizing compounds such as polyphenols and polyunsaturated fatty acids as potential prebiotics, provided they meet the criteria of selective microbiota utilization and demonstrated health benefits.
How do prebiotics work?
Prebiotics act as a food source for specific microorganisms in the gut, supporting their growth and activity. This selective utilization is crucial, as not all dietary fibers or compounds qualify as prebiotics. The benefits of prebiotics are linked to their ability to modulate gut microbiota, which in turn influences various health outcomes, including improved digestion, enhanced immune response, and reduced inflammation. Importantly, prebiotics can also have effects outside the gut, such as on the skin or oral cavity, further broadening their potential applications.
Scientific and regulatory challenges
Establishing a compound as a prebiotic requires rigorous scientific evidence. Two key criteria must be met:
- Selective utilization: The compound must specifically support beneficial microorganisms. This can be demonstrated through detailed studies using molecular and analytical methods to track microbiota changes.
- Health benefit: The compound must confer a measurable health benefit, supported by randomized controlled trials (RCTs) in the target population.
Despite advancements in microbiome research, challenges remain in conclusively linking microbiota changes to health outcomes. Experimental designs must account for confounding factors, individual variability in microbiota composition, and differences in dietary habits. Moreover, regulatory requirements for using the term “prebiotic” vary globally, adding to the complexity.
Prebiotic compounds
Fructooligosaccharides (FOS) and inulin are among the most extensively studied prebiotics. These non-digestible carbohydrates are found in plant-based foods such as chicory root, onions, garlic, and bananas. Due to their resistance to enzymatic digestion, they reach the colon intact, where they selectively nourish beneficial bacteria like Bifidobacterium and Lactobacillus. Their health benefits include improved gut motility, enhanced mineral absorption, and strengthened immune responses. These compounds are widely used in dietary supplements and functional foods.
Galactooligosaccharides (GOS), naturally present in human breast milk and some dairy products, are another well-researched type of prebiotic. They promote the growth of beneficial bacteria, particularly Bifidobacterium species, and are known to support infant gut development, alleviate symptoms of irritable bowel syndrome, and enhance immune function. GOS is commonly added to infant formulas and gut health supplements.
Resistant starch, found in foods like green bananas, cooked and cooled rice, potatoes, and legumes, is a type of starch that resists digestion in the small intestine. Once in the colon, it ferments and produces short-chain fatty acids (SCFAs), such as butyrate, which support colon health. Resistant starch has been shown to improve insulin sensitivity, enhance satiety, and aid in weight management, making it a popular choice for metabolic health products.
Human milk oligosaccharides (HMOs), complex carbohydrates found exclusively in human breast milk, are vital for early-life gut microbiota development. They selectively nourish Bifidobacterium species and provide protection against gastrointestinal infections by preventing pathogen adhesion. Synthetic HMOs are now included in infant formulas to mimic the benefits of breastfeeding.
Polyphenols, plant-derived compounds found in fruits, vegetables, tea, coffee, wine, and chocolate, have also demonstrated prebiotic potential. These compounds modulate gut microbiota composition and provide antioxidant and anti-inflammatory effects. Their health benefits include cardiovascular support and gut microbiome modulation. Polyphenols are increasingly incorporated into functional beverages, supplements, and even skincare products.
Beta-glucans, soluble fibers found in cereals like oats and barley as well as in mushrooms and yeast, are another type of prebiotic. They partially ferment in the gut, supporting beneficial bacteria. Beta-glucans are known to lower cholesterol levels, improve immune function, and reduce postprandial blood glucose levels. They are widely used in heart-healthy foods and immune-support supplements.
Pectins, derived from fruits such as apples and citrus fruits, are soluble fibers that partially ferment in the colon. They stimulate the production of SCFAs, like butyrate and acetate, which improve gut motility and reduce inflammation. Pectins are commonly used in supplements targeting digestive health.
Arabinoxylans and arabinoxylan oligosaccharides (AXOS) are prebiotic fibers derived from the bran of cereal grains like wheat, rye, and barley. They selectively support the growth of beneficial bacteria such as Bifidobacterium. These fibers enhance the production of SCFAs, support immune modulation, and contribute to metabolic health. They are often included in fiber-rich cereals and baked goods.
Lactulose, a synthetic disaccharide made of galactose and fructose, resists digestion in the upper gastrointestinal tract. It is widely used in medical settings to treat constipation and reduce ammonia levels in patients with hepatic encephalopathy. Lactulose also promotes the growth of beneficial gut microbiota.
Emerging prebiotics continue to broaden the scope of this field, including novel compounds like peptides, amino acids, and certain lipids. These developments promise applications that extend beyond gut health, potentially targeting metabolic and mental health.
The effectiveness of prebiotics depends on their dose, method of delivery, and the individual’s specific health needs. While traditional prebiotics like inulin and GOS are widely available, newer compounds like HMOs and polyphenols offer targeted benefits.
Practical applications and safety
Prebiotics can be incorporated into various foods, supplements, and even medical interventions. Their stability during food processing and the compatibility with different delivery matrices are important considerations. While generally safe, prebiotics can cause mild gastrointestinal discomfort in some individuals, particularly at higher doses.
The effectiveness of a prebiotic depends on its dose and the method of delivery. Research indicates that doses ranging from 5 to 20 grams per day are typically required to achieve significant health benefits. However, individual responses may vary, emphasizing the need for personalized approaches to prebiotic supplementation.
Future directions
As the understanding of the microbiome deepens, new methods, such as metagenomics and metabolomics, are being employed to study prebiotic effects in greater detail. Advances in statistical analysis and machine learning are also aiding in identifying biomarkers that predict individual responses to prebiotics. These developments hold promise for more targeted and effective use of prebiotics in clinical and dietary applications.
Conclusion
Prebiotics represent a powerful tool in promoting gut health and overall well-being by selectively modulating the microbiota. However, their development and use require adherence to rigorous scientific standards to ensure efficacy and safety.
For individuals seeking to optimize their gut health through prebiotics, consulting with a gastroenterologist such as Dr. Christos Zavos is highly recommended. Dr. Zavos, a board-certified gastroenterologist and hepatologist based in Thessaloniki, Greece, offers personalized consultations to guide patients in choosing the most suitable prebiotic interventions for their unique needs. To schedule an appointment or learn more, contact Dr. Zavos via the contact form on peptiko.gr, call (+30)-6976596988 or (+30)-2311283833, or email czavos@ymail.com.
Reference
- Hutkins R, Walter J, Gibson GR, Bedu-Ferrari C, Scott K, Tancredi DJ, Wijeyesekera A, Sanders ME. Classifying compounds as prebiotics – scientific perspectives and recommendations. Nat Rev Gastroenterol Hepatol 2024 Oct 2.