Gut Health 101: Probiotics, Prebiotics, and More!

  • TurtleTree
  • |
  • April 4, 2021
Gut Health 101: Probiotics, Prebiotics, and More!

Gut health is an important part of our overall well being.

We are discovering more and more every day about how our gut health influences the rest of our bodies. Much like our skin, the gastrointestinal lining is the body’s first defense against the environment. However, this thin lining is fragile and can be easily disrupted by genetic, dietary, and environmental factors. Changes to gut homeostasis can lead to chronic inflammation, poor nutrient absorption, abdominal pain, and even gastrointestinal cancers. Many diseases are associated with the gastrointestinal tract, such as irritable bowel syndrome, inflammatory bowel disease, ulcerative colitis, peptic ulcers, and can all lead to lower quality of life and poor health outcomes.

And with the discovery of the gut-brain axis, in which the intestinal system has been found to be neurologically linked to the cognitive and emotional centers of the brain, researchers are realizing that the gut plays a major role in our mental and psychological health. For example, the neurotransmitter serotonin is responsible for stabilizing mood, feelings of well-being, and happiness. 95 percent of serotonin is found in the gastrointestinal tract and may be one of the mediators of the gut-brain axis.

Despite the extensive research done on gut health, the subject remains complex due to the numerous factors that affect the gut. However, studies show that one major aspect involved in gut health is the gut microbiome.

The Complexity of the Gut Microbiome

The gut microbiome consists of every microorganism that lives in the human gastrointestinal tract, which include bacteria, fungi, viruses, and protozoa. There are a hundred trillion of these microorganisms that reside in the gut, more than six times the number of cells in the human body. The vast array of microbial species and genetic material that live in the human gut far outstrips the complexity of the human genome. The number of bacterial species alone are between 300 and 500 with a total of two million genes.

Each microorganism is involved in hundreds of complex interactions with its neighboring cells, whether that’s sending out genetic material to communicate, releasing enzymes to digest food, engulfing one another, or producing compounds that kill other microorganisms and carve out a niche territory in our guts. These biological activities also affect the human body, as our intestinal walls must constantly interact with these microorganisms and protect our bodies from any potential harm. The human body has also co-evolved with many symbiotic microorganisms that provide our gastrointestinal tract with many benefits to our immune system and brain.

Much of the way that the human body has evolved to maintain a healthy microbial ecosystem is by encouraging and sustaining the growth of friendly bacteria and other microorganisms that can outcompete with potentially pathogenic bacteria, and to a smaller extent, fungi. While several harmful bacteria naturally reside in the human gut, their numbers are low enough that the body’s natural defense can keep them from entering other parts of the body. That’s because many other neutral or friendly bacteria species are endlessly producing compounds that suppress the growth of these pathogenic bacteria. Their naturally high population also allows them to consume nutrients faster, preventing pathogenic bacteria from gaining a foothold.

These friendly bacteria can also produce a number of compounds that improve the health of the body, such as enzymes, amino acids, vitamins, and other nutrients. However, when bacterial counts are decimated by the prolonged use of antibiotics, they may not recover as quickly as more virulent bacteria. This can cause an imbalance in the gut microbiome and lead to disease. For example, Clostridium difficile normally resides in the gastrointestinal tract in low numbers and is suppressed by other microbial species. However, this bacteria can infect and inflame the colon after a course of antibiotics, causing colitis, abdominal cramps, and life-threatening diarrhea.

What Are Probiotics?

Studies have shown that certain bacterial species, when administered to those suffering from C. difficile infection, can be used to treat the disease. These types of beneficial bacteria are known as probiotics.

Essentially, probiotics are living microorganisms that give the human body health benefits or even treat an infection when consumed. Most probiotics are bacterial species, with a few yeast species clinically shown to exhibit health benefits as well. These microorganisms can be found in certain fermented foods such as yogurt, kefir, sauerkraut, kimchi, aged cheese, and miso. The major probiotics species that have been isolated and documented for their health effects are found in seven core genera – Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus. The potential benefits of probiotics range from treating diarrhea to reducing eczema in children.

Commercial probiotics are selected strains of microorganisms from these genera that have been packaged in a delivery vehicle such as a pill or fermented beverage. Effects are also specific to individual strains, which are genetic variants of bacteria from the same species. For example, there are the Bifidobacterium infantis 35624 and HN019 strains, both of which come from the same species but have different properties. There are other strains that belong to the B. infantis species that may have no effect at all, and so not all probiotics are created equal. Research is still ongoing on the classification and health benefits of different species and strains.

And What About Prebiotics?

Prebiotics are a type of dietary fiber made from strings of sugars that the body cannot digest but probiotics can selectively feed on. Prebiotics provide health benefits by increasing the population of probiotic strains. While many pathogenic bacteria and other microorganisms cannot digest prebiotic fibers, probiotics can produce enzymes that break down these dietary fibers and use them as fuel. Part of the benefit of including fibers in a healthy diet is the selective growth of probiotics in the gut.

Some examples of prebiotics include fructans such as inulin, galacto-oligosaccharides, resistant starch, pectic oligosaccharides, and human milk oligosaccharides. Many prebiotics come from natural sources like vegetables, grains, fruits, milk, seaweed, and beans. However, due to their low concentration in food, prebiotics are often manufactured industrially by combining sugars with specific enzymes that link the sugars together.

Products that contain probiotics together with prebiotics are known as synbiotics. By delivering the probiotic microorganisms alongside their fuel source, these synbiotics can improve the viability and beneficial effects offered by the probiotic strain.

There’s Also Postbiotics!

Postbiotics are the waste products of probiotics after they consume prebiotics and other carbohydrates found in the gastrointestinal tract. These postbiotics are one of the ways that probiotics confer their health benefits. For example, many probiotics produce a series of compounds known as short-chain fatty acids (SCFAs). The simplest and most common SCFA is acetic acid, which is the acid found in vinegar. Others include propionic acid and butyric acid, which are common acids found in aged cheese.

SCFAs have been documented to reduce the risk and symptoms of IBD, cardiovascular disease, colorectal cancer, obesity, and diabetes. SCFAs act by increasing the acidity of the colon, which prevent pathogenic bacteria from gaining a foothold. SFCAs also provide energy to colon cells and other beneficial bacteria, improve mineral absorption, and promote the excretion of bile acid for digestion. SFCAs have also been shown to act as chemical messengers that promote metabolism, neural regeneration and plasticity.

Postbiotics also include enzymes, proteins, peptides, vitamins, polysaccharides, and other organic acids produced as side products of probiotic metabolism. There is even a type of postbiotic which is essentially just a dead probiotic cell, also known as paraprobiotics or “ghost” probiotics. These dead cells have also been shown to provide immunological health benefits, despite the fact that the inactivated probiotics are unable to reproduce or generate metabolic products.


Gut health involves the complex interplay of an entire microbial ecosystem that lives in our gut. Researchers continue to uncover more about how these microorganisms affect our bodies and how we can modify our own gut microbiome to improve our health. Later on, we will dive deeper into how to change the gut microbiome using foods and diet, and what that means for our daily lives, including the role played by the microbiome on the gut-brain axis. Stay tuned!