Could better gut health be your best defence this winter?

Could better gut health be your best defence this winter?

Did you know that 70-80% of your immune system lives in your gut? Most people think the gut microbiome’s job ends with digestion, but it plays a far bigger role in how your body defends itself against illness. Every day, your gut and immune system are in constant communication, working together to protect you from harmful invaders while keeping the peace with friendly microbes and food particles.

Here, we’ll explore how the gut and immune system work hand in hand, why gut microbiome diversity is critical for long-term immune health, and what you can do to support this powerful partnership.

What is the immune system?

You can think of your immune system as a highly trained security team. It’s made up of organs, cells and proteins that patrol your body, ready to respond to viruses, bacteria, or other unwelcome guests. It has two main branches:

• Innate immunity: these are your first responders. They act fast, tackling invaders as soon as they appear.
• Adaptive immunity: the detectives. They remember past infections and plan smarter responses next time.

A balanced immune system is powerful but measured. When it isn’t functioning as it should, several things can happen: it may fail to mount an adequate defence when genuinely needed, leading to more frequent or prolonged infections; or it may activate when there is no real threat, reacting to everyday substances as though they’re harmful.

Sometimes the immune system misidentifies normal things, such as pollen, certain foods, or even your own tissues as dangerous. This can occur for a number of reasons, including genetics, previous infections, environmental load, a disrupted gut microbiome, or ongoing inflammation. When this happens, the immune response becomes dysregulated, contributing to conditions like allergies, asthma, or autoimmune disease.

The aim isn’t to “boost” the immune system, but to support it so it can function optimally; responsive enough to fight infections, yet calm and regulated enough to avoid inappropriate reactions.

The gut: home to your body’s defences

The gut is one of the busiest immune hubs in the body, with around 70-80% of immune cells located within the gastrointestinal tract. This is where the gut-associated lymphoid tissue (GALT) acts as a central training ground for immune cells, teaching them how to respond to different substances they encounter every day.

Living alongside this immune network is your gut microbiome, a bustling community of bacteria, fungi, viruses and archaea. From birth, your gut microbes and immune system develop together, constantly talking to each other. This relationship helps train immune cells to tell the difference between harmless substances, such as food or beneficial microbes, and genuine threats like harmful viruses and pathogens.

Think of it as a lifelong education system for your immune defences. Early exposure to a variety of microbes – from the outdoors, diet and social interactions – helps shape the diversity and resilience of your gut microbiome and, in turn, your immune responses. Without this constant training, the immune system can overreact to harmless stimuli, increasing the risk of allergies or autoimmune conditions.

How the gut and immune system communicate

Communication between the gut and immune system happens in both directions, forming what researchers call the gut–immune axis. The gut microbiota constantly sends signals to immune cells through chemical messengers and metabolites, keeping the immune system informed and balanced.

One of the most important communication tools is a group of compounds called short-chain fatty acids (SCFAs). These are produced when beneficial gut bacteria break down dietary fibre in the large intestine. SCFAs, such as butyrate, acetate and propionate, play a vital role in regulating inflammation and strengthening the gut barrier, preventing harmful microbes from entering the bloodstream.

This cross-talk helps the immune system maintain a state of homeostasis, or balance. When the gut microbiota becomes disrupted – for example, through antibiotics, chronic stress, poor diet or illness – this communication can break down, leading to inflammation and reduced immune resilience.

The importance of gut microbiome diversity

A healthy immune system depends on a balanced gut microbiome. Each community of gut bacteria plays its own role, from training immune cells to producing SCFAs and keeping harmful microbes in check. The greater the diversity, the better your body may be able to respond to challenges and maintain balance.

Gut diversity is influenced by both modifiable and non-modifiable factors. Things like diet, physical activity, sleep and stress management are within your control, while age and genetics are not. As we get older, gut diversity naturally tends to decline, which can affect immune function. This makes healthy lifestyle habits even more important over time.

The good news is that, unlike genetics, there are so many things we can do to improve the diversity of our microbiota. Simple changes include:

• Eating a wide variety of plant-based foods, aiming for around 30 different plants a week
• Including high-fibre foods such as oats, beans, lentils, fruits, vegetables, nuts, and seeds
• Eating fermented foods (e.g., yoghurt, kefir, sauerkraut, kimchi), which may help increase beneficial bacteria
• Managing stress and prioritising good-quality sleep
• Supporting the gut during and after antibiotic treatment with probiotics such as Lactobacillus rhamnosus GG (LGG®)
• Spending time outdoors, especially in nature-rich environments like parks, gardens, and forests
• Staying physically active on a regular basis
• Limiting ultra-processed foods, which are associated with reduced microbial diversity

Supporting your gut–immune connection

Did you know that children catch an average of 5–8 colds per year, while adults experience 2–3 a year? Supporting your immune system through nutrition, lifestyle and targeted supplements can help reduce the impact of these seasonal challenges.

Two evidence-based live bacterial strains have been scientifically shown to support the upper respiratory tract during the winter months, by enhancing mucosal immunity and supporting IgA, the first line of defence in the nose, throat and airways:

• Lactobacillus rhamnosus LGG®, the world’s most documented bacterial strain
• Bifidobacterium lactis BB-12®, the world’s most published Bifidobacterium strain

Vitamin D₃, an important vitamin that contributes to the normal functioning of the immune system, is particularly important to supplement during the months of October to March, because we simply cannot get enough of it from the sun in the UK.

And don’t forget those essential omega-3 fatty acids, which help support a healthy gut environment and reduce inflammation, so if you don’t regularly eat oily fish, a supplement may be worth considering. Key nutrients such as vitamin C, zinc, iron and vitamin A also play important roles in immune cell function, gut barrier repair and antioxidant support – ideally obtained through a diverse and balanced diet. Always discuss with a healthcare professional first if you think supplementation is needed.

Balance is everything

The gut and immune system are deeply interconnected. A diverse, well-nourished gut microbiome helps train, regulate and support your immune defences – not by “boosting” them, but by maintaining balance. By nurturing your gut through diet and lifestyle, you can strengthen your immune resilience and support your overall wellbeing all year round.

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