Nutrition Research > Gut Health


Quick Facts

Gut health is important, and goes beyond good digestion. Gut health impacts overall health.

Eating whole grains, like wheat, can positively impact gut health by helping achieve a balanced microbiome.

Good gut health can have positive long-term health implications, such as reduced disease risk, improved brain health, and a well supported immune system.

What is gut health?

“The gut” is your digestive tract, also known as the alimentary canal. It is a long tube of connected organs starting at your mouth and moving through the esophagus, stomach, small intestine, large intestine, colon and anus.

Gut health is traditionally measured by motility (transit time, stool frequency, stool consistency), histology (structure of cells), permeability of the gut, and other measures of compounds in the stool or tissues.

Researchers are beginning to measure gut health based on the composition and diversity of gut bacteria. Bacteria in the digestive system are important for the digestion and absorption of food and its nutrients, but they also play a key role in modulating disease.

A proper balance of bacteria – more beneficial bacteria and fewer opportunistic bacteria – is important for good gut health, and is increasingly being recognized as influencing overall health.

What is the human gut microbiota?

All of the microorganisms in the human gut, including bacteria, are known as the human gut microbiota. The understanding of the human microbiota’s role in health and disease is evolving as more research is being done.

Human microbiome vs. gut microbiome vs. gut microbiota

  • Human microbiome is the term used to describe the trillions of different microbes, including their genes and their metabolic activity, that live in and on the human body. Those microorganisms (mostly bacteria, but also others like fungi and viruses) can vary based on their location.
  • Gut microbiome is the term used to describe the trillions of different microbes, including their genes and their metabolic activity, that are found in the gastrointestinal tract.
  • Gut microbiota, typically refers to the microorganisms themselves.

Microorganisms are found throughout the gut, and their concentration increases along the gastrointestinal tract, with smaller numbers in the stomach, and very high concentrations in the colon.

Each person’s microbiome is unique to them, and there are many factors at play in shaping the composition of intestinal microbial communities. These include colonization history (how gut microbes become established from infancy onward), exposure to microbes from animals, dietary intake, and the environment. Humans are essentially sterile before they are born. The transfer of microbes during birth and in the first years of life have a lasting impact on the composition of intestinal microbial communities. Simply put, the first microbe that can occupy a specific niche is usually able to defend its niche against other microbes that arrive later.

After colonization history, diet is the second most important determinant of intestinal microbiota. A diverse diet that is rich in plant-based, minimally processed food provides fibre and plant phytochemicals to support a diverse microbial community. Intestinal microbiota respond very rapidly – within days – to changes in dietary intake.

Impact of food and nutrients on gut health

Dietary intake can affect gut microbiota by changing:

  • The microbiota abundance (amount of bacteria)
  • The microbiota diversity (types of bacteria)
  • The metabolites of the gut microbiota (production of short chain fatty acids)

By eating foods that contain whole-grains and certain other foods high in dietary fibre, you can positively impact your gut microbiota.

Probiotics vs Prebiotics vs Postbiotics

Probiotics are defined by the World Health Organization as “live microorganisms which when administered in adequate amounts confer a health benefit on the host.” In other words, they are good microbes. Although often thought to include fermented foods like kombucha or kimchi, very few fermented foods meet the definition of a probiotic. That’s because probiotic activity is strain specific. Fermented foods with live active cultures are only considered probiotic if the food contains at least one strain that meets the criteria as being probiotic and has a well-studied species known to provide probiotic health benefits. Unfortunately, many fermented foods labeled as probiotic have undefined strains, at variable levels, that have health benefits have not been documented. Food sources of probiotics include some yogurts and kefir with specific strains of microbes.

Prebiotics are undigestible fibres that stimulate the growth or activity of certain good bacteria in the large intestine. In other words, they are fuel for our gut microbiota. Whole grain foods and certain other foods high in dietary fibre, like wheat, are a source of prebiotics.

Prebiotic fibre is metabolised by gut bacteria in a process called fermentation, producing short-chain fatty acids (SCFA), which can;

  • Reduce gut pH creating optimal conditions for the growth of good bacteria
  • Interact with the gut barrier, improving the protection it provides
  • Enhance absorption of minerals
  • Provide energy for our gut bacteria and for us

Postbiotics are an emerging concept defined as a preparation of non-living microorganisms and/or their components that confers a health benefit on the host. They are being explored as a means of reducing the risk of disease and improving health. While research supporting the use of postbiotics is promising, more evidence is needed to understand and support their role in human health.

Research Spotlight: Wheat & Gut Health

Consuming grains, and wheat in particular, has been shown to have a positive effect on gut health.

A recent systematic review showed that as little as 6 g, (about 2 Tbsp) of wheat bran per day promoted gut microbiota diversity.

In another systematic review of human studies over 20 years, consuming as little as 8 g of wheat bran per day showed favourable changes, including increased gut microbiota abundance, diversity and metabolites.


Foods high in FODMAPs, which includes wheat, can exacerbate symptoms of Irritable Bowel Syndrome (IBS), resulting in some patients limiting intake of these foods. An unintended consequence is a low-fibre diet, which can negatively impact gut bacteria. Wheat-containing foods that are processed or fermented to reduce their FODMAP levels, such as sourdough fermented bread, may be better tolerated by people with IBS, allowing them to enjoy those foods and benefit from the fibre in wheat.

To learn more about FODMAPS, visit the Canadian Digestive Health Foundation.

Grains, gut health, and colorectal cancer

Colorectal (bowel) cancer is the second-leading cause of death from cancer in men and the third-leading cause in women in Canada. It is estimated that almost half of the cases of colorectal cancer could be prevented through healthy lifestyle changes.

Studies show that consuming whole grains can decrease the risk of colorectal cancer, and this link is stronger in people without a history of colon cancer or polyps. A recent review of 99 studies, including data on 29 million people, of whom over 250,000 were diagnosed with colorectal cancer, found that whole grains independently lower cancer risk. Specifically, consuming approximately 90 g of whole grains per day (about 3 servings) reduces cancer risk by 17%.

Another review study found that the consumption of 10 g of cereal fibre per day was associated with a 9% decrease in colorectal cancer risk.

Emerging Research

A recent study looked more closely at how dietary fibre and phytochemical components of wheat bran work to combat colon cancer. The results showed that the dietary fibre and phytochemical components of wheat bran work in a synergistic manner to combat colon cancer, at levels that we can achieve in our daily diet. This means consuming wheat-based foods will not only provide nutrients, but also fibre and phytochemicals that may contribute toward reducing colon cancer risk.

Grains, gut health, and brain health

Researchers are studying the potential effect of eating whole grains, including whole wheat, on the brain and mental health.

Emerging research is looking at how microbes in the gut are connected and impact the brain. This connection is often referred to as the gut-brain axis. The gut-brain axis is a two-way communication network between the enteric (gut) and central nervous systems.

The network is made up of both physical (nerves) and chemical (neurotransmitters) connections between the brain and the gut. The network communication allows the brain to influence gastrointestinal activity and also allows the gut to influence brain activity (such as mood, cognition, and mental health).

A recent review study summarized the evidence from human studies that examined the association between dietary fibre intake and brain health. It concluded that diet quality, including adequate intake of dietary fibre, can influence cognitive performance, mental health, and brain function.

SCFAs, products of fibre fermentation, appear to be a key route of communication between the gut microbiota and the brain, as they support intestinal barrier integrity and regulate gastrointestinal immune cells.

Though more high-quality human studies are needed to understand the relationship between the fibre from wheat-based foods and the gut-brain axis, the emerging research is promising.

Grains, gut health, and immunity

Eating whole wheat can play a key role in immune health by providing a rich source of dietary fibre and beneficial phytochemicals.

Wheat bran, the outer layer of the whole wheat kernel, is a source of antioxidants and dietary fibre, known to enrich and diversify intestinal microbial communities.

A rich and diverse gut microbiome can impact immune health in a variety of ways:

  • Gut microbes and their metabolites improve the integrity of the gut’s mucosal barrier, reduce inflammation, and increase resistance to pathogenic microbes. This effect is partially related to fibre fermentation, as the products of microbial fermentation (SCFAs) are an important energy source for colonic mucosa.
  • When gut microbes have a source of energy from dietary fibre, they are much less likely to harvest energy from the glycoprotein that makes up the gut’s mucus layer. This layer acts as a protective shield against potentially pathogenic microbes.
  • Fibre fermentation reduces the pH of the gut, reducing proliferation of potentially pathogenic microorganisms.
  • Gut microbes train our immune system and can prevent infections. Regular exposure to gut microbes can train our immune system to attack pathogenic microbes, and to spare microbes that are beneficial for our health.

The beneficial properties of whole wheat can be further improved by long sourdough fermentation. This slow fermentation process recruits microbial and cereal enzymes, which increases the availability of fibre by transforming insoluble fibre to soluble fibre. This transformation also increases the availability of manganese, magnesium and other minerals.


Wheat as a Prebiotic: Gut Health & Research Spotlight

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