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Alex Cook - Sports and Endurance Dietitian

Can Your Diet Make Your Immune System Stronger?

There are currently lots of articles in the press about how we can “boost” our immune system, especially with the emergence of COVID-19. However, the simple truth is a healthy balanced diet makes all bodily functions more efficient, including immunity. Sadly there is no specific superfood that can turbocharge your immune system. No one food is recommended over another and a healthy balance is best. Here are a few steps you can take to make sure you are giving your body what it needs to remain healthy and strong:



Training hard and not eating correctly isn’t great for your body. Your immune system can become suppressed during periods of low calorie intake or weight reduction. So if you are prone to illness, and you are looking to lose weight, it is advisable to do so slowly and during non-competitive training phases when your training volume is lower (2).

In general, eating a varied diet with an appropriate intake of carbohydrates, protein, vitamins and minerals is an important and simple step to ensure an optimally functioning immune system. If you are energy deficient your immune system may suffer and you may be more susceptible to upper respiratory tract infections (URTI). A healthy immune system benefits from a diet adequate in calories, high in fresh fruit and vegetables, omega 3 fats, nuts and whole grains. Having three good meals a day and recovery meals/snacks that contain carbs (50g) and protein (20g) post-training will help keep the body in top form. Keep hydration levels up. Drink regularly throughout the day (moderate tea and coffee intake also count) and ensure that you hydrate correctly after training.


Studies have found that carbohydrates can play an important role in maintaining effective immune function. Low carbohydrate intake may cause direct immunosuppression as immune cells function best on glucose alone. So ensuring adequate carbohydrate intake throughout the day and especially after exercise will help support the immune system. For example, after training you could have: a bagel, nut butter and banana or a bottle of Berry Beast or Big Red which contains around 50g carbohydrate per serving.

Additionally, ingestion of carbohydrate during prolonged/intense levels of exercise can reduce the production of cortisol as a response to training. Cortisol has been linked with immune suppression. If an athlete is training fasted or in an intentionally low glycogen state, it is not advised to do this for more than a few days at a time. If they are prone to illness and bugs, it is not advised to do it at all until their immune system is back at full strength.

Staying hydrated during exercise has multiple benefits. Firstly, it prevents dehydration (no surprises with that one) and secondly, it ensures saliva flow is maintained. Saliva is important as it contains antimicrobial properties, so if saliva flow decreases there is a chance that we can become more susceptible to infection from viruses and bacteria (1).


A study in the American Journal of Clinical Nutrition (3) showed how supplementation of 600mg Vitamin C per day for three weeks prior to a 90km ultra-marathon race reduced the incidence of URTIs (upper respiratory tract infections) during the two week recovery period. Vitamin C has antioxidant properties which help counteract the impact of damaging free radicals that are produced as a result of intense exercise. If you manage to have plenty of fruit and vegetables in your diet then supplementation should not be necessary.

It is also good to remember fruit and vegetables that are canned, frozen or dried also count as do fruit and vegetables it in a smoothie. For example, the EXALT range are a great way of working towards your five-a-day ensuring that you are boosting your Vitamin C and antioxidant intake to meet your daily requirement.


Probiotics or “friendly bacteria” have been getting more and more attention over the years. Whether you are fermenting your own food or taking a supplement, we are much more aware of how significant our bowel health plays in so many aspects of our wellness. A double-blind study in the International Journal of Sport, Nutrition and Exercise Metabolism (4) supplemented 84 endurance athletes with either a probiotic or placebo over four months of winter training. They measured the incidence of URTI in both groups. The number of athletes that experienced one or more weeks of URTI was 36% higher in the placebo group compared to those who took a probiotic. Athletes should look out for probiotics that contain at least 10 billion live species of lactobacillus and bifidobacterium. If you don’t want to take supplements, try using live natural yoghurt or foods such as sauerkraut and kefir.


Vitamin D is recognised as having an important role in immunity and helps to defend against the common cold. Vitamin D deficiency is common in athletes, especially in winter months (as a result, so are colds) Between the months of October and March, individuals are advised to supplement every day with 10 mcg of Vitamin D a day.


  • Don’t skip meals and avoid negative energy balance. Overall energy intake should match your requirements. Don’t shy away from carbohydrate and if you are doing fasted training / training low, only do it for a few days at a time.
  • Consider taking carbohydrate during training (30-60g/hr). Taking this in fluid form also helps maintain hydration and saliva flow.
  • Ensure regular intake of protein (20g per meal per day) and focus on post-training meals (0.3g/kg of body weight).
  • Regular intake of fruit, vegetables and salads (try for at least five-a-day, seven is even better if you can). If you think you will struggle with this consider taking a multivitamin.


1. Gleeson M 2016 Immunological aspects of sport nutrition. Immunology and Cell biology 94 117-123

2. Nieman DC et al 1996 Immune response to obesity and moderate weight loss Int. J Obesity relatedMetab. Discord, 20:353-360

3. Peters EM et al Vitamin C supplementation reduces the incidence of postface symptoms of URTI in ultra marathon runners Am Journal Clinical Nutrition 57: 170-174

4. Gleeson M, Bishop NC, Oliveira M, Tauler P 2010 Daily probiotics (Lactobacillus casei Shirota) Reduction of infection incidence in athletes. International Journal of Sport Nutrition and Exercise Metabolism, 1-10

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