Believe it or not, people who exercise frequently or for prolonged periods are more likely to pick up infections and catch colds than sedentary people.
This is even more likely in autumn and winter – the traditional season for a triathlete to increase the volume of his or her training in order to build a strong base of fitness for the summer season ahead.
Minor infections and colds may not seem serious in themselves, but they can severely disrupt your training and dampen your enthusiasm to train when the weather turns wet and cold.
That's why it's important to watch what you eat at this time of year to help keep your immune system fighting fit.
A single hard training session causes temporary depression of immune function that can last up to 24 hours, effectively leaving an open window for bugs to multiply relatively unchecked.
Periods of prolonged training can lead to long-term depression of immune function and this is associated with increased rates of infection, particularly upper-respiratory-tract infections such as coughs and colds.
When you exercise, you naturally produce a certain amount of stress hormones – adrenaline and cortisol are the ones you've probably heard of. These are thought to be the cause of immune suppression. The harder or longer you train, the more stress hormones you produce.
And if you exercise without sufficient fluid or fuel – in the form of stored carbohydrate (glycogen) or dietary carbohydrate – you'll produce even more stress hormones. But when a heavy training schedule puts pressure on your immune system, you can ensure that you make healthy diet choices.The key to maintaining an efficient and effective immune system is to consume enough of the nutrients that play a vital role in building immunity.
There is convincing evidence that dietary nutrients such as glucose, protein, fat and glutamine play an important role in supporting immune function. While minerals such as iron, zinc, and vitamins A, E, B6 and B12 are also important for the maintenance of a healthy immune system.
It's also true, however, that an excess of individual vitamins and minerals – such as iron, zinc and vitamins A and E – can impair your immunity and actually increase your risk of infection.
A few simple checks and tweaks to your diet will ensure that your immune system is firing on all cylinders – with the result that your performance will be stellar too.
1. ENERGY IN: Eat enough calories to meet your daily energy needs
An insufficient calorie intake has been shown to reduce immune function, reduce muscle glycogen stores and reduce the effectiveness of training sessions. Few of us know exactly how many calories we need on a day-to-day basis but keeping an eye on your weight is a useful measure.
If you are losing weight week after week and not intending to, it probably means you are not eating enough. Similarly, if you are gaining weight week after week, you're likely to be eating more calories than you burn.
2. STOP BEFORE YOU POP: Avoid immune-boosting pills
The evidence for taking supplements such as bovine colostrum, zinc and echinacea to boost immune function in athletes is inconclusive. Glutamine may decrease the incidence of infection but is only beneficial to athletes who have a true glutamine deficiency – an uncommon problem.
A vitamin C supplement doesn't have any effect on the incidence of colds in the general population but some evidence suggests it could benefit people who do hard exercise, however a study of marathon runners taking 1000mg of vitamin C per day (25 times greater than the RDA) found no effect on the incidence of colds. Swap the pills for a varied diet.
3. CARBO LOADING: Consume carbohydrate during training sessions of more than 90 minutes
Consuming carbohydrates during intensive or endurance sessions helps to reduce the release of stress hormones and prevents the suppression of immune function. Aim to consume 30g to 60g of carbohydrate per hour while you are exercising.
You could use a combination of solid food and liquids on the bike but you are probably best to stick to liquids while running and swimming to avoid stomach upsets. Ready-made isotonic sports drinks are perfect for the job but you could also try any of the handy drinks and snacks outlined in this table.
|Clever carb consumption||Carb content
|Isotonic sports drink (eg Lucozade, Powerade, Gatorade)||32g per 500ml
|350ml unsweetened fruit juice + 350ml water + 0.8g salt||35g
|Energy gel (eg SIS, High 5, Power Bar)||23-26g
|4 tbsp raisins||30g
|Energy bar (eg SIS, High 5, Power Bar||39-45g
|1 large flapjack||50g
4. VARIETY PERFORMANCE: Consume adequate vitamins and minerals
A diet that provides enough energy, is well-balanced and varied will probably give you all the vitamins and minerals you need. Remember the government's ‘five-a-day' message, and aim to eat different coloured fruits and vegetables to get the maximum benefits – the different colours mean they contain a variety of beneficial nutrients. One portion is 80g of fresh, frozen or canned fruit and vegetables, one tablespoon of dried fruit or one glass of fruit juice or smoothie.
If you are vegetarian or vegan, avoid eating red meat, or are female, you may struggle to consume enough iron – since the iron in plant food is more difficult to absorb than the iron in meat. Include some of these iron-rich foods in your diet so you can boost your intake:
If you eat plant sources of iron have a vitamin C-rich food – citrus fruit or juice, salad, vegetables, peppers, potatoes and strawberries – at the same time to improve the absorption.
- Eggs, oily fish – such as canned salmon, sardines
- Dried apricots and figs, prunes and raisins
- Spinach, watercress and rocket
- Frozen peas, curly kale and spring greens
- Pumpkin, sesame and sunflower seeds
- Cashew and pine nuts
- Fortified breakfast cereals
5. LESS IS MORE: Do not overdo your vitamin and mineral intake
A number of studies have found that taking huge doses of vitamins and minerals may actually have the effect of impairing your immune function.
If you do decide to take a supplement, choose a multivitamin and mineral supplement that provides no more than 100 per cent of the recommended daily allowance (RDA) for each nutrient. Supplementation recommendations unrelated to exercise – such as folic acid for women who are pregnant or trying to conceive – should still be followed.
The use of single-nutrient supplements is not recommended and you should seek the advice of a sports nutritionist or dietitian if you really are thinking about using single-nutrient supplements.
6. A FINE BALANCE: Find the right balance of energy-giving nutrients
An imbalance between carbohydrate, protein and fat intake can affect immune function if the intake of one nutrient is excessively high at the expense of the other two. Consuming inadequate protein impairs immune function, but the majority of triathletes are unlikely to be deficient if they are following a well-balanced and varied diet. Vegetarians and vegans, women and people trying to lose weight are most at risk of protein deficiency.
Male triathletes should consume 1.2g to 1.4g protein per kg body weight per day, females need around 15 per cent less than males. So a 70kg male triathlete should consume 84g to 98g of protein per day; while a 70kg female triathlete would need 70g to 84g of protein per day.
Starting a long training session with low-carbohydrate stores causes a large rise in stress hormone production, and as already discussed, this causes depression of the immune function. To ensure you have sufficient fuel to train and recover, triathletes training for one to two hours per day should aim to consume 5g to 7g of carbohydrate per kg body weight per day, those training a little less (three to five hours per week) need around 5g of carbohydrate per kg body weight per day. A 50kg triathlete training one hour per day would need 250g to 350g of carbohydrate per day.
Omega-6 and omega-3 polyunsaturated fatty acids are also essential nutrients. Research suggests that omega-3 fats improve the symptoms of patients with diseases characterised by an over-active immune system - thus omega-3 fatty acids are thought to be anti-inflammatory. Triathletes are advised to consume oily fish – such as sardines, tuna, salmon, and mackerel – at least once per week.
7. IN THE DRINK: Consume fluids when training or racing
Drinking will help to prevent dehydration – which has been proven to cause an increased release of stress hormones – but it also helps to maintain the all-important saliva flow during exercise. Saliva contains anti-microbial properties which fight bugs at one of their points of entry into the body.
By sipping fluids at regular intervals, you'll improve saliva flow into the mouth. Use plain water or sugar-free squash for short training or racing sessions, follow tip 3 for fuelling longer or more intense sessions and don't forget to drink 150-200ml fluids every 20 minutes.