What are prebiotics?

A prebiotic is an indigestible food component that selectively promotes the growth or function of a specific group of bacteria in the colon. This stimulation leads to beneficial changes in the composition or activity of the gastrointestinal microbiota, ultimately enhancing the host’s overall health. This definition was established during the 6th Meeting of the International Scientific Association of Probiotics and Prebiotics (ISAPP) in 2008.¹

Prebiotics vs probiotics

• Prebiotics traverse the digestive tract intact since our digestive system lacks the enzymes necessary to digest them. Eventually, they reach the colon where beneficial bacteria reside. The bacteria are able to convert the prebiotics into nourishment that supports their growth and well-being. 
• Probiotics are living bacteria grown in a laboratory for use as supplements. Similar to the beneficial bacteria found naturally in our bodies, they thrive in our digestive tracts when we consume them, whether as food or supplements.

Importance of gut health

The human gastrointestinal system is home to over 100 trillion microorganisms, primarily bacteria but also viruses, fungi, and protozoa. The microbiome is best understood as a virtual organ of the body. The human genome has approximately 23,000 genes, but the microbiome harbours over three million genes that generate thousands of metabolites. These metabolites supplement numerous host functions, so impacting the host's phenotypic, fitness, and overall health.²

A number of critical aspects of human health, including innate immunity, hunger regulation, and energy metabolism, are influenced by the gut microbiota. Probiotics and dietary fibre that target the gut microbiome can improve health outcomes and potentially lower obesity. However, the gut microbiota can be adversely affected by substances including medications, food additives, antibiotics, and pesticides. Thus, it is imperative that the microbiota is viewed as an integral part of nutrition, leading the medical community to revise public health messaging and educational programmes in line with this understanding. Furthermore, consuming fibre has been repeatedly associated with a host of health advantages, highlighting its significance in a diet that is balanced.²

Understanding prebiotics

Types of prebiotics

Prebiotics are available in various forms. Most of them are carbohydrates such as fructans, galacto-oligosaccharides (GOS) and starch-derived oligosaccharides. Essentially, prebiotics belong to the category of oligosaccharide carbohydrates (OSCs).¹ 

• Based on chain length, fructans with varying degrees of complexity, such as inulin and fructooligosaccharides, selectively activate gut flora. 
• GOS, which are generated from lactose, greatly increase Lactobacilli and Bifidobacteria, particularly in newborns. 
• Another prebiotic called resistant starch (RS) encourages the synthesis of butyrate, which benefits different Firmicutes and other gut flora. An oligosaccharide generated from glucose called polydextrose has the ability to stimulate Bifidobacteria. 
• Depending on their source, pectic oligosaccharides (POS) derived from pectin (soluble fibre from fruits) display a variety of structures and advantages. 

Substances that aren't carbohydrates, such as flavanols generated from cocoa, also satisfy prebiotic requirements by promoting lactic acid bacteria. These varied prebiotics highlight how important they are for gut health and microbial regulation.¹

Sources of prebiotics

Foods high in prebiotics, which are essential for human health, include seaweeds, onions, garlic, and asparagus. They are manufactured, mostly as fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS), because their natural content is minimal. 

• Aspergillus niger and other important bacteria are used in the manufacture of an enzyme that increases yield. 
• Galactosyl-transferase and galactosidase are enzymes used to manufacture GOS obtained from sources like Lactobacilli and Aspergillus oryzae. Production efficiency is increased by lab-made forms of β-galactosidase derived from organisms such as Bacillus subtilis and E. coli, although there are particular hurdles and optimisation requirements associated with each technique.¹

Mechanism of action

Prebiotics give the gut bacteria energy sources, which changes the microbiome's makeup and functionality. Functional metagenomics, which involves analysing human microbiota genes, has demonstrated that various bacterial species, including distant ones like E. coli, often possess the ability to produce specific prebiotics. Prebiotics can traverse the digestive tract intact because our digestive enzymes cannot degrade them. Ultimately, they reach the colon where beneficial bacteria reside. Some species, like Actinobacteria, Bacteroidetes, and Firmicutes, ferment FOS, GOS, and XOS. Others, like Bifidobacterium sp., ferment starch and fructans. 

Fermentability is influenced by the length of the carbohydrate’s chain: shorter chains, like FOS, are more widely fermentable than longer ones, like inulin. Cross-feeding is the process by which the fermentation byproducts of one species act as a substrate for those of another. By producing fermentation products that change the microbial composition and encourage the creation of butyrate, prebiotics also lower the pH of the gut. These mechanisms, known as butyrogenic actions, promote intestinal health. Diffusing into the bloodstream, short-chain fatty acids (SCFAs, from prebiotic breakdown) affect distant organs and systems in addition to the gut, helping to maintain general health.¹

Short-chain fatty acids (SCFAs) can also be created by bacteria in the skin and vagina. The gut microbiota primarily produces SCFAs through the fermentation of dietary fibre. The three main SCFAs are butyrate, propionate, and acetate; research on their bioactivities has been extensive. Numerous health advantages of SCFAs include their immunoregulatory, anti-inflammatory, anti-obesity, anti-diabetic, anti-cancer, cardiovascular, hepatoprotective, and neuroprotective properties.³

Health benefits of prebiotics

Microbiota and gut health

Prebiotics encourage the growth of helpful gut microbes by entering the colon undigested. In spite of their low pH and prolonged transit time, they facilitate significant microbial colonisation in the colon, supporting intricate digestion processes.⁴

Prevention of gastroenteritis

Prebiotics increase the good bacteria in the intestines, which may help avoid gastroenteritis brought on by bacteria like E. coli and Salmonellae.⁴

Inflammatory bowel disease

The treatment of inflammatory bowel disease (IBS) may benefit from prebiotics. For example, probiotic combinations and germinated barley foods both lower inflammation and increase good bacteria. However, depending on the circumstances and mode of administration, some prebiotics, such as FOS, may make symptoms worse.⁴

Reduction of cancer risk

Prebiotics reduce the risk of cancer by blocking the activity of harmful enzymes that damage genetic material. They encourage the growth of good bacteria that boost butyrate and create less toxic enzymes, maintaining healthy colonocytes and causing cancer cells to undergo cell death.⁴

Bone mineralization

Prebiotics improve the body's capacity for calcium absorption, which may aid in the prevention of osteoporosis. The majority of supporting data comes from animal research, with a few positive human trials.⁴

Cardiovascular effects

Insulin concentrations and serum lipid levels can be lowered by prebiotics such as inulin (fructan) and GOS. Research on blood glucose and cholesterol levels reveals conflicting results, but it also suggests significant benefits for the cardiovascular system, especially in lowering triglycerides and LDL in hyperlipidemic patients.⁴

Incorporating prebiotics into your diet

Start slowly

Introduce prebiotics gradually to avoid bloating and gas as your gut microbiota adjusts. Avoid a sudden increase in consumption.

Timing matters

Because your gut microbes are more active during the day and your body follows a circadian rhythm, it is best to avoid taking prebiotics late at night in order to optimise benefits and reduce discomfort.

Consider digestive health

Prebiotics from stone fruits (peaches, mangos, cherries) should be avoided if you have digestive problems, such as IBS. These prebiotics can be more difficult to digest.

Embrace natural sources

Incorporate prebiotics into your diet from natural sources like fruits and vegetables. These foods improve your general health by supplying fibre, vitamins, minerals, and probably prebiotics.

Current research and future directions

Prebiotics were first identified as having the ability to specifically ferment carbohydrates in order to increase Lactobacilli and Bifidobacteria in the colon, which led to various health benefits. Advances in research approaches have expanded the range of prebiotics to include genera that produce short-chain fatty acids (SCFAs), essential for many body functions, such as Roseburia, Eubacterium, and Akkermansia. New prebiotics made of plants, animal-derived substrates, yeast, polyphenolics, and other micronutrients are emerging, although classic prebiotics like fructans and galacto-oligosaccharides still have a significant market share. New prebiotics may be developed from sustainable sources like food waste, and functional improvements could result from treatments. Prebiotics also exhibit potential in treating diseases like ulcerative colitis and colorectal cancer by influencing the microbiomes of the skin and oral cavity, among other areas. Prebiotics are becoming more and more popular as bioactive supplements, as evidenced by clinical trials that have examined their effects on obesity, autism spectrum disorders, ageing, and other conditions.⁵

Summary

Prebiotics are essential for maintaining a healthy gut microbiota because these organisms preferentially digest carbohydrates, which feeds good bacteria like Lactobacilli and Bifidobacteria. They improve digestive health, and may even lower the chance of developing chronic illnesses like cancer and heart problems. Consuming foods that grow naturally, such as fruits and vegetables, gives you important nutrients and may also contain prebiotics that support general health. Considering specific sensitivities, such as those with irritable bowel syndrome (IBS), it's crucial to introduce prebiotics gradually in order to prevent stomach pain. The basis of general health and vigour is excellent gut health, which is supported by emphasising a balanced diet high in fibre and a variety of prebiotics. Proactively feeding your gut prebiotics can have long-term advantages for your microbiome and other health issues.