The Gut–Immune Connection: Why Your Microbiome Matters More in Winter

Winter often brings a rise in colds, flu, a touch of COVID, but overall slower recovery and lower energy. While many people blame the weather alone, the gut actually plays a major role in how well the immune system responds at this time of year. The gut and immune system are closely linked, and the bugs living in your gut help shape how your body reacts to viruses, inflammation and stress.

For women living with PCOS, this connection is especially important. Gut health influences inflammation, metabolic balance, cravings, hormone regulation and resilience, all of which can feel more sensitive during winter.

How Gut Health Shapes Immunity

Around seventy per cent of the immune system sits in and around the gut. The gut lining acts as a physical barrier, while immune cells monitor what enters the body. A healthy microbiome helps regulate inflammation, supports nutrient production, and contributes to a calm, balanced immune response.

When the microbiome becomes disrupted, the immune system may overreact or become less efficient. This can mean slower recovery from viruses, greater sensitivity to seasonal changes and more fatigue.

Winter brings natural shifts that can challenge the gut. Less sunlight (so less vitamin D0, dietary changes, comfort eating, reduced movement, and increased stress all influence the gut microbial environment and may alter immune resilience.

Microbiome Diversity and Immune Defence

A diverse microbiome is linked with stronger immune defence, better metabolic balance, reduced inflammation and improved digestion. Lower diversity is associated with greater susceptibility to infections and inflammatory conditions.

Some beneficial bacteria can work to strengthen the gut barrier. When the barrier is strong, the immune system remains calm and balanced. When it becomes compromised, the immune system becomes more alert and inflammation can rise.

Women with PCOS often show lower microbial diversity and higher inflammation. This can contribute to fatigue, cravings, hormonal symptoms and reduced winter resilience.

Prebiotics and Probiotics Explained

Prebiotics are fibres that feed beneficial gut bacteria. They help increase diversity and support the production of short chain fatty acids that regulate inflammation. Examples include garlic, leeks, onions, asparagus, oats, flaxseed and green bananas.

Probiotics are live microorganisms found in fermented foods. They help introduce and maintain beneficial species. Examples include kefir, sauerkraut, kimchi, miso and live yoghurt.

Including even one or two sources of these foods daily can support a healthier microbiome.

Digestive Issues That Affect Immunity: Dysbiosis, SIBO and Reflux

Gut health is not simpply about what you eat. Digestive symptoms can also influence the immune system, inflammation and overall wellbeing. Winter often brings these issues to the surface because the body is under more seasonal stress.

Dysbiosis

Dysbiosis refers to an imbalance in gut bacteria in our microbiome. This may involve too few beneficial microbes, too many inflammatory species or microbial patterns that contribute to excess gas or digestive discomfort.

Signs can include bloating, irregular bowel movements – diarrhoea and/or constipation, fatigue after meals, sugar cravings and skin flare ups. Dysbiosis is associated with inflammation and can influence insulin sensitivity and hormonal balance.

SIBO (Small Intestinal Bacterial Overgrowth)

SIBO occurs when bacteria that belong in the large intestine migrate into the small intestine. This can interfere with digestion and nutrient absorption.

Common signs include bloating that worsens through the day, abdominal discomfort, diarrhoea or constipation, nausea and persistent food reactions. SIBO is often assessed through a breath test which measures hydrogen or methane gases produced by gut bacteria.

Reflux and Upper Digestive Issues

Reflux, heartburn and upper abdominal discomfort can also affect the gut–immune connection. These symptoms may relate to imbalanced gut bacteria, delayed stomach emptying, stress or certain trigger foods.

Reflux can reduce sleep quality and contribute to inflammation, both of which weaken immune resilience. Supporting digestion through balanced meals, eating slowly and avoiding late eating can help.

When Testing Can Help

Testing is not always required, but it can be helpful for people with ongoing digestive symptoms.

Comprehensive stool tests: These provide information on microbial diversity, beneficial and opportunistic bacteria, digestion and absorption markers, inflammation levels and yeast overgrowth.

Breath tests for SIBO: These measure hydrogen and methane gases produced after a specific carbohydrate substrate is ingested. This helps determine whether bacterial overgrowth may be contributing to symptoms.

These tools help build a clearer picture of what is happening in the gut and can guide more personalised nutrition and lifestyle strategies. If you are interested in any of this testing, please do get in touch.

Best Foods for a Winter Proof Gut

Focusing on gut friendly foods at this time of year supports both digestion and immunity.

• Fibre rich vegetables: Aim for a wide range including carrots, kale, leeks, beetroot, broccoli and Brussels sprouts.
• Fermented foods: Include kefir, live yoghurt, sauerkraut or kimchi a few times per week.
• Polyphenol rich foods: Berries, apples, olive oil, green tea, herbs and spices help modulate inflammation.
• Healthy fats: Omega 3 rich foods such as salmon, sardines, walnuts and flaxseed support immune balance.
• Protein: Protein helps stabilise blood sugar and supports immune cell function.

These foods help create a microbiome that is more resilient and better equipped to support your immune system through winter.

Bringing It All Together

Your gut plays a central role in how well your immune system copes during winter. A diverse and balanced microbiome supports a calmer immune response, steadier energy, healthier digestion and lower inflammation. Digestive issues such as dysbiosis, reflux or SIBO can place extra strain on the gut–immune axis which is why symptoms often feel more noticeable during colder months.

This connection matters even more for women with PCOS. Gut health influences inflammation, insulin sensitivity and hormone regulation, which means that an imbalanced microbiome can make PCOS symptoms feel stronger. Research shows that women with PCOS are more likely to experience dysbiosis and lower microbial diversity, and this can contribute to cravings, fatigue, irregular cycles and higher inflammatory markers. Supporting the gut is therefore not only helpful for immunity but also for managing the wider metabolic and hormonal picture of PCOS.

By focusing on simple, consistent changes such as increasing fibre, including fermented foods, supporting digestion and reducing ultra processed foods, you can strengthen your microbiome and support both immune and hormonal balance. Many women notice fewer flare ups, more stable energy and improved symptoms when they support their gut in this way.

If you feel run down every winter, struggle with digestion or suspect your microbiome needs more attention, this is an ideal time to start making changes. Or if you’d like to know more, why not get in touch?