Today RunningPhysio welcomes guest blogger Julia Mainstone to the site. Julia specialises in nutrition for fitness and sport and is a professional member of the American College of Sports Medicine. She works as Sports Nutritionist for Brighton and Hove FC and has provided support for triathlons, Ironman and the Marathon des Sables. You can follow Julia on twitter – @JuliaNutrition and find out more information on nutrition on her website –

So you thought exercise makes you fitter? It does overall. Exercise has massive benefits for the cardio-respiratory system, not to mention many other health benefits. However, as training loads and volumes increase, we open up possibilities for different complications. One of the key areas where changes are observed in elite athletes is the immune system and their pattern of illness.

It is now accepted that exercise causes altered immune cell function. This is a fairly new area of research in Sports Medicine, and there’s still a lot of work needed before we come anywhere near understanding what’s going on. Despite being great for our overall health, exercise causes decreases in the region of 15-25% in lymphocytes, T cells and B cells, natural killer cells, and reduces the mucosal secretory functions of the nose and salivary glands. There is thought to be an ‘open-window’ of susceptibility to infection after acute exercise, although the length of this period is debatable. For more information about the immune system and the physiological changes induced by exercise, read this excellent consensus statement.

Upper respiratory tract infections (URTIs) are common in runners and endurance athletes, and are one of the most frequently cited reasons for attendance at sports medicine clinics. Infections don’t necessarily follow normal patterns of winter illness and tend to peak at times of hard training and competition. In particular, they increase 2-6 fold after marathons and ultramarathons. Other areas of the body such as the intestine also suffer during intense exercise, although how these factors are related is still unknown.

It’s clear from the physiological changes observed in athletes that exercise has a measurable impact on markers of immune stress and dysfunction. So what are the practical nutritional steps you can take to minimise these risks?

Don’t forget your carbs…

Cycled carbohydrate intake is vital for performance in endurance sports, and carbohydrate intake leading up to a marathon is the biggest predictor of performance in novice runners. However, it’s not just performance they affect. Ingestion of carbohydrates plays a role in how the immune system responds to heavy training loads by reducing circulating cortisol level and delaying the symptoms of overreaching during intensive training periods(Gleeson 2004, Lane 2009). Placebo-controlled trials in cyclists have also shown carbohydrate ingestion attenuates some aspects of detrimental changes of immune response during prolonged exercise (Halson 2004). Up to 60 g of carbohydrate per hour of heavy exertion helps dampen immune inflammatory responses, as described in the second part of the Immune System Consensus Document .

So, one strategy to reduce immune stress is to ensure adequate fuelling with carbohydrates. Start well-fuelled, refuel during exercise lasting longer than an hour, and make sure you provide your body with proper recovery nutrition afterwards. Starting well-fuelled requires a good suppply of healthy carbohydrates throughout training and tapering periods. Despite what Panorama has to say about how useless sports drinks are, if ever they have a place, it's during competitive long-distance events. They can be vital if you find it hard to eat whilst running, especially if your goal is to excel at, rather than just complete an event. It goes without saying that food should provide as much of our energy intake as possible, but during long endurance exercise, if there was a choice between no additional fuel or fuel provided by a sports drink, I’d take it every time. Following exercise, try to eat a balanced meal containing a good amount of protein and carbohydrate as soon as possible.

Good general nutrition…

It may seem like an obvious point to make, but the importance of all-round good nutrition cannot be stressed enough. Ensuring your diet contains adequate energy, macronutrients (protein, carbohydrate and fat) and micronutrients (vitamins and minerals) is one of the most important things you can do for your general health and to keep your immune system strong. Eating a balanced wholefood diet and avoiding energy and micronutrient deficiencies (particularly iron, zinc and vitamins B6 and 12), is essential for athletic performance. Many micronutrient supplements have been found to increase immunity in athletes, but it is unclear whether this is because they are treating deficiencies or providing additional benefit to non-deficient subjects. A good diet preventing micronutrient deficiencies is the best starting point, and vitamin and mineral supplements should ideally only be used for those with proven deficiencies or poor diets.

Lose weight carefully…

A study in judo athletes found that four weeks of weight-loss, averaging 2.8kg, was enough to significantly weaken immune function and increase the risk of URTI. If you are reducing the amount of carbs in your diet to lose body fat, you may need to scale down your endurance training because your body will not cope well with an energy deficit, low-carbohydrate intake and high levels of training. Aim for shorter higher-intensity workouts and make sure you include carbohydrates at key times around exercise. If your fat-loss strategy includes depleted workouts, make sure you have a carbohydrate-containing meal afterwards. If you are restricting your energy intake it is particularly important to make sure every calorie counts and provides you with essential nutrients, so cut out all junk food and get the majority of your calories from lean meats and fish, fresh fruit and vegetables and low-fat dairy products.


Maintaining a good state of hydration will help protect your first-line defences against infection- namely your snot and spit! Being well-hydrated reduces stress in exercise and also maintains saliva flow, which is useful because saliva contains several substances with antimicrobial properties such as IgA (immunoglobulin A). Click here to read the American College of Sports Medicine's fluid replacement guidelines for exercise. You should aim to never lose more than 2% of your body mass during exercise, which can easily be checked at home or at the gym.

Probiotics and other supplements

A good diet with enough energy and macro/micronutrients is one of the biggest building blocks for a strong immune system. However there are some supplements other than micronutrients that have shown benefit in certain athletic populations.

Probiotics are defined by the World Health Organisation as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host.” They are found in some yoghurts and can also be bought in supplement form. Various Lactobacilli species have been tested in athletes, and studies have shown probiotics from this group reduce fatigue and themagnitude of acute exercise-induced changes in some cytokines, maintain salivary IgA during winter training and competition and reduce frequency and severity of URTI in runners. Probiotics may also reduce the severity of gastrointestinal symptoms in marathon runners.

Quercetin has been suggested as an immune system strengthener and as an exciting supplement for immune support. However despite increases in plasma quercetin levels, a study published in 2011 showed quercetin did not counter postexercise inflammation or immune changes relative to placebo. Other work, published in 2007 showed quercetin ingestion by ultramarathon athletes for 3 weeks before a competitive 160-km race significantly increased plasma quercetin levels but failed to attenuate muscle damage, inflammation, increases in plasma cytokine and hormone levels, and alterations in leukocyte cytokine mRNA expression.

Other supplements that have been suggested for improving immunity in athletes include echinacea, ginseng, beta-glucan, and bovine colostrums. For a full discussion of the possible efficacy of these supplements please read the second part of the consensus paper.

The bottom line….Maintaining good immune health requires a holistic approach. Periodisation of training and nutrition, particularly in periods of fat-loss, reducing stress levels, sleeping and eating well all play an important role.

Whilst the supplements I have discussed here are all thought to be safe when taken as directed, it's always sensible to be cautious about adding supplements to your diet. Discuss with a qualified professional or do your homework before taking anything new.



  1. […] Look after your body – try and include some flexibility work in your schedule to stretch out tight, aching muscles. This might be stretches after your run or a foam roller session once or twice a week. Also swimming, sauna or steam room can really help. Don't underestimate the value of a little pampering – get a good massage done if you can afford it. It doesn't have to be the painful deep tissue kind – often a relaxing massage can work wonders. Nutrition can also play a big part in keeping you healthy, and looking after your immune system. […]

  2. Whilst most of the article was very informative the idea that we should NEVER lose more than 2 % body weight is plain wrong- elite marathon runners are the most dehydrated at 7+% dehydration.
    Yes the ACSM’s recommendation is to keep hydration less than 2% but they are also wrong – Tim Noakes’s book Waterlogged has debunked this myth with hundreds or studies to back it up. Its time nutritionists and the ACSM revise this policy in the face of overwhelming evidence to the contrary.

    Otherwise it was a very informative interesting article

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