Introduction
As South Africa moves into the colder months, respiratory infections such as influenza become more common. South Africa’s influenza season generally occurs between April and October, although the exact timing varies from year to year. In 2026, the National Institute for Communicable Diseases (NICD) reported that the influenza season began earlier than usual, in the week of 9 March.
Most seasonal advice focuses on measures such as vaccination, hand hygiene, staying home when ill and appropriate medical care. These remain important. But there is another part of the body worth considering when thinking about overall immune health: the gut.
The gut and immune system are closely connected. However, this does not mean that eating a particular food can “boost” your immunity overnight or prevent you from catching the flu.
Instead, research suggests that nutrition, the gut microbiome, sleep, physical activity and other lifestyle factors can all interact with immune function. Supporting these fundamentals is a more realistic goal than looking for a quick immune-boosting solution.
Why Does the Gut Matter for Immunity?
The digestive system is much more than a tube that processes food. Large amounts of immune tissue are located around the gastrointestinal tract.
One important component is gut-associated lymphoid tissue (GALT). It acts as an important site where the immune system encounters and responds to substances coming from the gut. GALT includes structures such as Peyer’s patches and other lymphoid follicles.
The gut microbiome also interacts with the intestinal immune system. Microorganisms and their metabolic products can influence immune signalling and the integrity of the intestinal environment.
This relationship works in both directions: the immune system helps regulate the microbial community, while microbes and their products can influence immune responses.
That is why scientists are increasingly interested in the gut-lung axis – the idea that interactions between the gut, microbiome and immune system may have implications beyond the digestive tract, including respiratory health.
Importantly, however, researchers are still working out exactly how these relationships translate into meaningful health outcomes in humans.
What Does the Research Show?
The evidence is strongest for the general importance of a healthy diet and adequate nutrition rather than for any single “immune-boosting” food.
Dietary fibre is particularly interesting because some types of fibre are fermented by gut microbes, producing compounds called short-chain fatty acids (SCFAs). These compounds can influence the intestinal environment and immune signalling.
A 2026 systematic review of human research examined non-digestible carbohydrates and prebiotics in relation to immunity, infections, inflammation and vaccine responses. The authors found evidence of effects on some immune and inflammatory outcomes, but also highlighted differences between studies and the need for further research.
This is an important distinction: supporting normal immune function is not the same as preventing infection.
You can have a nutritious diet and still catch influenza. Your immune system is not a shield that makes you invulnerable to viruses.
Can Probiotics Help During Flu Season?
Probiotics are live microorganisms that can provide health benefits when consumed in adequate amounts and when the specific microorganism has been shown to have an effect.
Some research has investigated whether probiotics can reduce respiratory infections.
A 2022 systematic review and meta-analysis of 42 papers involving more than 9,000 adults found that probiotics modestly reduced the risk, duration and severity of respiratory tract infections compared with placebo. However, most of the included studies had some concerns about risk of bias, and the effects varied between studies.
Another systematic review of six randomised controlled trials involving 1,551 adults also reported fewer upper respiratory tract infections among people taking probiotics, but the authors described the overall evidence as low quality and called for more research.
So while probiotics are an interesting area of research, it would be an exaggeration to say that taking a probiotic will prevent flu.
Different strains can have different effects, and evidence for one probiotic product cannot automatically be applied to another.
Fermented foods such as plain yoghurt or kefir can be part of a varied diet, but they should not be treated as medicines or substitutes for vaccination and appropriate medical care.
What Can Disrupt Gut-Supportive Habits in Winter?
Comfort eating
Cold weather can change eating habits. Warm, convenient foods may become more appealing, and some people may eat fewer fruits, vegetables and other fibre-rich foods.
There is nothing inherently unhealthy about enjoying winter comfort foods. The goal is simply to maintain variety.
Soups and stews can make this relatively easy. For example, a vegetable and lentil soup can combine vegetables, legumes and whole grains in one warming meal.
Less physical activity
Cold weather may also mean spending more time indoors and moving less.
Regular physical activity supports overall health and can also help maintain normal bowel function. You do not need an intense exercise programme to benefit from movement. Walking, household activities, stretching or indoor exercise can all contribute to your daily activity.
Sleep disruption
Sleep deserves particular attention during flu season.
A systematic review found that shorter sleep was associated with a higher likelihood of upper respiratory tract infections. The researchers estimated that people sleeping less than the usual 7-9 hour range had greater odds of experiencing an upper respiratory infection, although the evidence had limitations and does not prove that sleep duration alone causes infection.
Sleep is therefore part of immune-supportive health, alongside nutrition and other healthy behaviours.
Practical Ways to Support Gut and Immune Health
1. Eat a varied, fibre-rich diet
Try to include a mixture of:
- Vegetables
- Fruit
- Beans and lentils
- Whole grains
- Nuts and seeds
- Other minimally processed foods you enjoy and can afford
Variety matters because different plant foods provide different types of fibre and other compounds that interact with the gut microbiome.
If your usual diet is low in fibre, increase it gradually rather than making a sudden dramatic change.
For more information about prebiotics and probiotics, see the Gut Health SA Probiotics & Prebiotics Explained guide.
2. Include fermented foods if you enjoy them
Plain yoghurt, kefir and some traditionally fermented foods can be incorporated into a balanced diet.
However, fermented does not automatically mean probiotic. A food only provides a specific probiotic benefit when the relevant microorganisms have been studied and shown to provide that benefit.
Choose products based on your nutritional needs and preferences rather than assuming that every fermented food has the same health effects.
3. Stay hydrated
Cold weather can make thirst less noticeable, but your body still needs fluids.
Water is a straightforward choice, although tea, soups and other beverages can also contribute to total fluid intake.
Adequate hydration is particularly important if you are physically active, have a fever or are experiencing vomiting or diarrhoea.
4. Keep moving
Aim for regular movement throughout the week.
If outdoor exercise is unpleasant in cold weather, consider indoor options such as walking around a shopping centre, stretching, home workouts or other activities you enjoy.
The best form of activity is one that is realistic enough for you to maintain.
5. Protect your sleep
Try to maintain a reasonably consistent sleep schedule and create conditions that allow you to get enough rest.
Good sleep will not guarantee that you avoid influenza, but it is an important part of maintaining normal immune function.
6. Do not forget proven infection-prevention measures
Gut health should complement — not replace — established approaches to respiratory infection prevention.
Depending on your circumstances, these may include:
- Staying up to date with recommended influenza vaccination
- Washing or sanitising your hands regularly
- Avoiding close contact with people who are unwell where possible
- Staying home when you are sick
- Improving ventilation in shared indoor spaces
- Seeking medical advice when symptoms are severe or you are at higher risk of complications
The NICD provides South African influenza surveillance and guidance, including current information about circulating influenza viruses and seasonal activity.
Be Careful With Antibiotics
One of the most important distinctions during cold and flu season is the difference between viral and bacterial infections.
Influenza and the common cold are caused by viruses. Antibiotics treat certain bacterial infections and do not work against viruses. Using them when they are not needed can cause side effects and contributes to antimicrobial resistance.
Antibiotics can also affect the gut microbiome.
This does not mean you should avoid antibiotics when they are medically necessary. They can be lifesaving treatments for bacterial infections.
Instead, antibiotics should be used when a qualified healthcare professional determines that they are appropriate. Never stop a prescribed antibiotic course or alter your treatment without speaking to your healthcare provider.
What About Vitamin C and Other Supplements?
Vitamin C, vitamin D, zinc and other nutrients all have roles in normal immune function, but more is not necessarily better.
A deficiency can impair normal physiological function, while taking large doses when you are not deficient does not automatically provide extra protection against infection.
Supplements may be appropriate in specific circumstances, but they should not replace a varied diet, vaccination, adequate sleep or medical treatment.
Be particularly cautious with products marketed as “immune boosters”. Claims about preventing flu, strengthening the immune system or “detoxing” the body may be much stronger than the available evidence.
A Season-Long Approach, Not a Quick Fix
There is no single food that can make your immune system “strong”.
Instead, think of immune and gut health as something supported by a collection of everyday habits.
A useful winter checklist is:
- Eat a varied diet with plenty of fibre-rich foods.
- Include fermented foods if you enjoy them and tolerate them.
- Drink enough fluids.
- Keep physically active.
- Prioritise adequate sleep.
- Follow recommended vaccination advice.
- Use antibiotics only when medically indicated.
- Seek medical care when respiratory symptoms are severe or persistent.
For more practical, evidence-based information about digestive health, explore the Gut Health SA Gut Health Resources.
Conclusion
The gut and immune system are closely connected, but the science is more nuanced than the phrase “boost your immunity” suggests.
The gut microbiome interacts with immune tissue and may influence immune signalling, while nutrition, sleep and physical activity all contribute to the body’s ability to function normally.
Research into probiotics and respiratory infections is promising but does not justify treating probiotics or fermented foods as a replacement for proven flu-prevention measures.
As South Africa enters its seasonal period of increased respiratory illness, the most sensible approach is therefore a broad one: eat a varied diet, look after your gut, sleep well, stay active, follow recommended vaccination guidance and use appropriate medical care when you become ill.
Gut health is one part of the picture — not the whole picture.
Health Disclaimer
This article is intended for general educational purposes only and does not replace personalised medical advice, diagnosis or treatment. Gut health and immune function are influenced by many factors, and individual nutritional needs vary. If you have a chronic illness, take medication, are immunocompromised, or develop severe or persistent respiratory symptoms, speak to a doctor or other appropriately qualified healthcare professional.