As we move into colder months in the Southern Hemisphere, many people start asking:

• How do I prevent cold and flu?
• Why do I keep getting sick?
• How can I boost my immune system?

Before we dive in, you can listen to the full conversation here:

The Key Shift

It is about nurturing your gut microbiome every day - because this is what supports immune function over time.

Your immune system responds to the environment you create for your microbiome.

 

Your Gut Microbiome Is Central to Immune Function

Your immune system is deeply connected to your gut.

Around 70 to 80 percent of immune cells sit in and around the gut, constantly interacting with your microbiome. This interaction helps shape how your immune system develops and responds.

In germ-free models:

• Immune systems are underdeveloped
• Antibody production is reduced
• Immune responses are impaired

When microbes are introduced, immune function improves

Your microbiome helps train your immune system what to respond to and how to respond.

 

Why You Keep Getting Sick

Frequent illness is often not bad luck. It is a signal.

It reflects reduced immune resilience, meaning your ability to respond and recover is compromised.

Common contributors include:

• Poor sleep
• Chronic stress
• Low fibre intake
• Under-recovery
• Reduced microbial diversity

For example:

• Healthy adults exposed to rhinovirus were 2.9 times more likely to get cold symptoms if they slept less than 7 hours, compared to those sleeping 8 hours.
• Higher training loads are linked to reductions in protective secretory IgA, and higher infection risk.
• Dietary fibre intake is associated with the improvement in immune response and reduced inflammatory biomarkers.

In many cases, these factors are influencing your microbiome, which in turn shapes your immune response.

You do not just catch illness. You meet it with a certain environment.

Why “Boosting Immunity” Is Not the Goal

Immune function is about balance.

• Too much activation leads to inflammation
• Too little leads to infection risk

The microbiome plays a central role in maintaining this balance.

Your gut microbes:

• Support regulatory immune cells
• Produce short chain fatty acids that regulate inflammation
• Influence immune signalling pathways

This regulation is heavily influenced by the health and activity of your microbiome.

A well-functioning immune system is regulated, not overactivated.

 

The Gut–Lung Axis: How Your Microbiome Influences Colds and Flu

What you feed your microbiome can influence how your body responds to colds and flu.

Stress, Allostatic Load, and Your Microbiome

Chronic stress increases allostatic load, the cumulative strain placed on the body.

This impacts:

• Hormones
• Inflammation
• Gut function
• Microbiome composition

Over time, this can lead to:

• Reduced microbial diversity
• Increased inflammation
• Altered immune signalling

Many of these stress-related changes are mediated through shifts in the microbiome.

In human studies, higher perceived stress has been associated with lower gut microbiome diversity and shifts in key bacterial species linked to inflammation. For example, increased stress has been linked to higher levels of Escherichia/Shigella and reduced abundance of beneficial butyrate-producing bacteria, which are important for maintaining gut barrier integrity and regulating immune responses.

Experimental models also show that stress can alter the microbiome in ways that increase gut permeability and immune activation, contributing to a more inflammatory internal environment.

This matters because your microbiome is constantly sending signals to your immune system. When the microbiome shifts under stress, those signals change.

Stress changes your microbiome. Your microbiome shapes your immune response.

 

How to Support Your Immune System Through Your Microbiome

If you want to prevent cold and flu, the focus becomes simple: support your microbiome consistently.

1. Sleep

• Aim for 8-9 hours
• Supports microbiome diversity and immune regulation

2. Feed your microbiome

• Increase fibre intake
• Support microbial diversity
• Promote beneficial metabolites

3. Manage stress

• Reduce chronic load
• Protect the gut environment

4. Balance exercise

• Moderate training supports immunity
• Overtraining without recovery can suppress it

Start with Your Microbiome

Not sure where to begin? Take the Find Your Gut Match Quiz
https://www.fertile-gut.com/pages/quiz

This helps identify what your body may need to better support your microbiome and immune function.

 

Key Takeaway

If you want to:

• Prevent cold and flu
• Stop getting sick as often
• Support your immune system

Shift your focus from boosting → to building and from reacting → to nurturing.

Your immune system is shaped by your microbiome.
And your microbiome is shaped by what you do every day.

Support your microbiome daily, and you support your immune system.

Find Your Gut Match.

References

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Round JL, Mazmanian SK. The gut microbiota shapes intestinal immune responses during health and disease. Nat Rev Immunol. 2009 May;9(5):313–323.

Cohen S, Doyle WJ, Alper CM, Janicki-Deverts D, Turner RB. Sleep habits and susceptibility to the common cold. Arch Intern Med. 2009 Jan 12;169(1):62–67.

Trompette A, Gollwitzer ES, Yadava K, Sichelstiel AK, Sprenger N, Ngom-Bru C, et al. Gut microbiota metabolism of dietary fiber influences allergic airway disease and hematopoiesis. Nat Med. 2014 Feb;20(2):159–166.

Tan J, McKenzie C, Potamitis M, Thorburn AN, Mackay CR, Macia L. The role of short-chain fatty acids in health and disease. Adv Immunol. 2014;121:91–119.

Rico-González M, Pino-Ortega J, Clemente-Suárez VJ. Training load and immune system response: A systematic review. Healthcare (Basel). 2021 Feb 10;9(2):178.

Knowles SR, Nelson EA, Palombo EA. Investigating the role of perceived stress on bacterial flora, inflammation, and intestinal symptoms in irritable bowel syndrome. J Psychosom Res. 2008 Jul;65(1):91–95.

Karl JP, Hatch AM, Arcidiacono SM, Pearce SC, Pantoja-Feliciano IG, Doherty LA, Soares JW. Effects of psychological, environmental and physical stressors on the gut microbiota. Front Microbiol. 2018 Feb 27;9:2013.

Qi X, Li Y, Fang C, Jia Y, Chen M, Chen X, Jia J. The associations between dietary fibers intake and systemic immune and inflammatory biomarkers, a multi-cycle study of NHANES 2015-2020. Front Nutr. 2023 Aug 31;10:1216445.