Gut Health and the Microbiome: A Primer

The human gut microbiome has been called our "second brain," our "inner garden," and our "forgotten organ." While the metaphors vary, they all point toward the same scientific reality: the community of microorganisms living in the human gut is far more than a passive passenger. It is an active, dynamic ecosystem that influences digestion, immune function, mood, and overall health in ways that scientists are still working to fully understand. This article covers the essentials of what the microbiome is, what disrupts it, and what you can do to support it.

38 Trillion Organisms: The Scale of the Microbiome

The gut microbiome consists of an estimated 38 trillion microorganisms, including bacteria, viruses, fungi, and archaea, inhabiting the gastrointestinal tract, with the highest concentrations in the large intestine. The bacterial component alone encompasses thousands of species, and the total number of microbial genes in the gut outnumbers the human genome by a factor of approximately 150. Put another way, there are roughly as many microbial cells in the human body as there are human cells, and the vast majority of them live in the gut.

This sheer scale hints at the importance of the microbiome. A healthy, diverse microbiome, one with a broad range of bacterial species in balanced proportions, is associated with robust digestive function, effective immune responses, and even psychological wellbeing through the gut-brain axis.

What the Microbiome Does

The gut microbiome performs several functions that the human body cannot perform on its own:

• Digestion, gut bacteria ferment dietary fibres that human enzymes cannot digest, producing short-chain fatty acids (SCFAs) including butyrate, propionate, and acetate, which are absorbed and used by the body for energy and other functions
• Immune modulation, approximately 70% of the immune system is located in and around the gut. The microbiome plays a critical role in educating and regulating immune responses, helping distinguish between harmful pathogens and harmless food proteins
• Vitamin synthesis, certain gut bacteria synthesise vitamins including vitamin K2 and several B vitamins
• Gut barrier maintenance, butyrate produced by bacterial fermentation serves as the primary fuel source for colonocytes (colon cells), supporting the structural integrity of the gut lining
• Neurotransmitter production, gut bacteria produce and modulate levels of serotonin, dopamine precursors, and GABA, influencing the gut-brain axis

"A diverse gut microbiome is not just good for digestion, it is a foundational pillar of immune health, metabolic function, and even mental wellbeing. Protecting and nourishing it is among the most impactful things you can do for long-term health."

What Disrupts the Microbiome

Several common factors can reduce microbial diversity and tip the balance toward a less healthy microbiome, a state researchers call dysbiosis:

• Antibiotics, broad-spectrum antibiotics kill beneficial bacteria alongside the targeted pathogens, and it can take months to years for the microbiome to fully recover
• Low-fibre diet, gut bacteria depend on dietary fibre for fermentation. A diet low in plant foods starves the bacteria that maintain a healthy microbiome
• Chronic stress, the stress hormone cortisol affects gut motility and can alter the composition of the microbiome over time
• Poor sleep, emerging research suggests that sleep disruption affects the gut-brain axis and may negatively impact microbial diversity
• Highly processed foods, ultra-processed foods are often low in fibre and high in additives that research suggests may negatively affect the gut lining and microbiome composition

How Prebiotics Like Inulin Help

Prebiotics provide the most direct dietary strategy for supporting a healthy microbiome. Unlike probiotics (which introduce live bacteria), prebiotics feed the bacteria already present in the gut, particularly the beneficial species that are most sensitive to dietary fibre deprivation. Inulin from Jerusalem artichoke root, as found in Halden Life Fiber Balance, selectively promotes the growth of Bifidobacterium species, which are among the most health-associated bacterial genera in the human gut. This selective stimulation, combined with the broad fibre support provided by psyllium husk and chia seed powder, makes Halden Life Fiber Balance a scientifically grounded approach to daily microbiome support.