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Nutrition and Performance in Sport

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Christophe Hausswirth

Chapter 2. Nutrition, sport and health

Topic 8. Immunity

Eve Tiollier, Amélie Fosse, Christophe Hausswirth, Axel Heulin, Yann Le Meur, Véronique Rousseau et École Lenôtre

Texte intégral

Questions and answers

Key points
Although moderate sport reinforces the body’s immune system, intense sport increases the risk of infections, especially during competition periods.
Some minerals (copper, iron, selenium and zinc) and several vitamins (A, B6, B9, B12, C, D and E) are necessary for the immune system to function properly. They should primarily be obtained through food.
Some food elements appear to help limit the negative consequences of intense exercise on the immune system. These are probiotics and polyphenols, especially quercetin.

Does sport make you more resistant to or, on the contrary, more sensitive to infections?

1Exercise appears to have a protective effect on the body’s immune system. For instance, if we compare people who take part in sport and those who do not, the number of days of infections registered during the three months of winter are almost two-fold lower (-46%) in the athletes. However, the relationship between sport and risk of infection is not linear. Thus, “the more I train, the better protected I am” does not apply! On the contrary, while moderate training has a beneficial effect in terms of prevention, very intense sport greatly increases the risk of infection.

2Among infections, the type most commonly reported in athletes are respiratory infections (rhinitis, rhinopharyngitis, angina, bronchitis).

Is the risk of falling ill seasonal?

3Unlike in the general population, symptoms of infection do not appear in athletes on a seasonal basis, rather they are closely linked to competition schedules.

4Thus, the phase of intense training preceding a competition is one of the periods during which the risk of infection is increased, because in addition to the negative effect of intense exercise, other factors such as stress or lack of sleep also damage the immune system. In addition, if competitions take place abroad, exposure to unfamiliar environmental microorganisms enhances the risk.

5The days, or even weeks, following a competition are also a risk period, especially in endurance sports. Thus, during the two weeks following an intense endurance event, participants are twice as likely to get sick as people who have not taken part in this type of event. This phenomenon is part of the “open window” theory, according to which strenuous exercise leads to a weakening of the immune system for between 3 and 72 hours. During this period when the immune system is weakened, the athlete runs a higher risk of developing an infection.

Can diet weaken the immune system?

6A significant reduction in energy intake is associated with various upheavals in the immune system. For instance, it was shown that losing 2 kg body weight over two weeks affected some immune parameters. By the same token, the immune system is weakened in judokas combining physical exercise and calorie restrictions.

What minerals and vitamins are necessary for the immune system to function properly?

7The immune system is complex, and, to function optimally, requires a well-defined nutritional environment. In this respect, some micronutrients are necessary. These include vitamin A, some B vitamins (B6, B9, B12), vitamins C, D and E, as well as zinc, iron, copper and selenium. To maintain the immune system, the first step is to ensure appropriate levels of intake of these different micronutrients (see Fact sheet No. 11 Balanced diet, p. 358).

Can vitamin/mineral supplementation reduce the risks of infections?

8The most studied vitamin in this context is vitamin C. Increasing intake of vitamin C does not decrease the immune upheavals caused by physical exercise. The results of a meta-analysis show that vitamin C consumption does not have any preventive effect on respiratory infections except in the case of athletes performing intense exercise, especially when they are exposed to cold temperatures. However, when taken after the symptoms appear, vitamin C has no impact on the severity or duration of the infection.

9During the two months of winter, consuming cereals enriched in different minerals and vitamins thought to boost the immune system did not provide conclusive results, either for the immune system or for respiratory infections.

10In general, it is recommended that vitamin and mineral supplements be taken with care: indeed, it is not because a vitamin is necessary for the immune system to function correctly that increasing intake proportionally reinforces the immune system. On the contrary, some micronutrients can cause problems when taken in large amounts. This is the case with vitamin E, where supplementation in athletes caused the opposite of the expected effect. Therefore, although vitamin/mineral supplementation (corresponding to food intake) can be useful, megadoses (several dozen times greater than the Dietary Reference Intake) are really not recommended.

What exactly are probiotics and how are they useful?

11Probiotics are living microorganisms (mostly bacteria and yeasts) which, when consumed in sufficient quantities, have beneficial effects on health. They are mostly found in yoghurt or fermented milks, but they are also available as supplements.

12Probiotics have been shown to have two different effects in athletes: they limit respiratory infections and can help prevent intestinal disorders, especially “traveller’s diarrhoea”.

13For respiratory infections, interesting results were reported in athletes, with a 40 to 50% reduction in the number of infectious episodes or in the number of days of sickness in people consuming probiotics during the four months of winter compared to people who did not. However, this beneficial result is not systematic, and may be more relevant to athletes who are subject to recurrent infectious episodes. This is because probiotics appear to have a greater effect in people with an inefficient immune system. There is also a gender bias, with increased effects in male athletes.

14The other advantage of probiotics is their capacity to limit intestinal disorders. These microorganisms prevent diarrhoea, which is particularly useful for those having to adapt to unfamiliar environments, such as when athletes take part in international competitions. Probiotics also limit stress-related gastrointestinal disorders (abdominal pains and nausea/vomiting). Thus, they are potentially of great interest for stress-sensitive athletes, those subject to intestinal problems, or those taking part in competitions abroad. Nevertheless, probiotics should not be taken just before an event unless they have been tested beforehand, because they may initially cause slight intestinal discomfort, which normally disappears after seven to ten days. This may seem paradoxical, but it simply reflects the need for the digestive system to adapt to new bacteria.

15Although probiotics have numerous interesting properties for athletes, it is difficult to generalize their effect on the immune system because this differs from one bacteria to another. The effects of bacteria also depend on the immune status of the person ingesting it; there can thus be considerable inter-individual variations. This makes it difficult to give general recommendations. Supplementation with probiotics could be useful for athletes subject to recurrent respiratory infections or intestinal disorders, but medical advice should be taken before starting this supplementation. In addition, it is important to remember that no product, whatever its nature, should ever be used for the first time during a competition.

Can consuming energy drinks during exercise prevent infections?

16Consuming energy drinks during exercise is only partially effective in preventing infection. Even if they reduce some of the deleterious effects of exercise, particularly some inflammatory parameters, they have no impact on immune system parameters: therefore, they do not decrease the incidence of infections during high-risk periods.

What other nutritional factors can help prevent infections?

17An important number of food substances have been tested to see if they can eliminate the negative consequences of intense physical exercise on the immune system. The oldest studies analysed the effects of amino acids such as glutamine and branched-chain amino acids. Given the poor results obtained, research turned to other nutritional components like colostrum, omega-3 fatty acids (fish oil), β-glucans, some plants (echinacea, ginseng) and polyphenols (vegetable-derived substances which have beneficial properties for the body) such as quercetin, curcumin, and resveratrol.

18So far, the most promising results have been obtained with β-glucans, colostrum and some polyphenols, particularly quercetin. But the recent enthusiasm for these substances does not allow the necessary detachment to give precise recommendations.

19The hypothesis currently emerging is that the immune system is highly complex, and that a mixture of various potentially beneficial elements is probably more efficient than any single substance, even if taken in large amounts.

Practical applications

1. A solid base

Foods which are important for the immune system

Image 10000000000004000000017D4E7C55D9.jpg

2. Avoid weakening your immune system

20 During high-risk periods (training courses/intense training, competitions, winter):

21 Avoid restrictive diets

22 Have a sports drink during training (See Fact sheet N° 10 Hydration, p. 342)

3. Take care of your gut flora

23Probiotics are “friendly” bacteria. Eating them helps strengthen the immune system.

24 Where are probiotics found?

Image 1000000000000400000000D276A31C0F.jpg

4. Stock up on polyphenols

The advantages of polyphenols

25 Polyphenols are contained in some vegetables

26 They can help athletes because they play a role in boosting the immune system and preventing infections

Sources of polyphenols

Image 100000000000017F000000B740A7DA72.jpg

In particular
Red berries: blackcurrants, blueberries, raspberries, stawberries, red grapes
Vegetables: broccoli, cauliflower, spinach

Image 100000000000016E000000A470DAEDBE.jpg

  • 1 Drinking cranberry juice every day particularly helps to fight against recurrent urinary infections (...)

In particular
Green tea, (grape, pomegranate, citrus fruit, cranberry1) juice, alcohol-free beer

Image 1000000000000106000000BB4882AA12.jpg

In particular
Dark chocolate, sugar-free cocoa

Recipe

Guinea-fowl supreme with mixed nuts and seasonal vegetables

Image 10000000000001E2000001E18B7C48EE.jpg

Photo credit: Thibaut Ruggeri.

Image 100000000000014400000186BB603321.jpg

27Serves 2

28Preparation time: 45 minutes

29Cooking time: 30 minutes

Difficulty: Image 10000000000000510000001CF5A1C0A4.jpg

30Guinea-fowl

31 2 guinea-fowl supremes*

32 Salt and pepper

33 15 g dried apricots

34 10 g dried figs

35 10 g pitted dates

36* Supremes: poultry breast with skin

37Open the guinea-fowl supremes in two, from the side of the meat, and season. Chop the dried fruit and stuff each supreme before closing it again.

38Roast the almonds and hazelnuts in the oven at 180 °C.

39Crush the nuts.

40Brown the supremes on both sides with the shallots and olive oil.

41Add the veal stock and season.

42Mixed nuts

43 10 g almonds

44 10 g hazelnuts

45 10 g pistachio nuts

46 40 g shallots

47 10 g olive oil

48 60 g veal stock

49 Salt and pepper

50Vegetables

51 100 g baby potatoes

52 100 g carotts

53 100 g broccoli florets

54 200 g cleaned spinach

55 1 garlic clove

56 10 g olive oil

57 Salt and pepper

58Sprinkle the crushed nuts onto the skin of the meat and roast in the oven at 180 °C for 20 minutes.

59Peel and chop the carrots, then cook them, covered, in a saucepan of boiling, salted water.

60Wash the potatoes and boil them.

61Cook the broccoli in salted water.

62Wilt the spinach in a pan with a small amount of oil and the garlic for 5 minutes. Season and drain.

63Place the spinach in a mound in the centre of the plate, cut the guinea-fowl supreme in two and place it on top of the spinach. Arrange the vegetables around the mound. Add the gravy.

64Serve in a deep plate.

65Chef’s note

66This dish is particularly rich in micronutrients that boost the immune system. It easily covers the Dietary Reference Intake (DRI) for vitamin B9 and β-carotene, and provides half of the DRI for vitamin C, vitamin E and zinc. It is also a good source of copper and iron.

67Nutritional analysis per person

Energy (Cal)

Carbs (g)

483

24

Lipids (g)

Protein (g)

19

54

Image 10000000000001570000017B511D77E1.jpg

68Raspberry, blueberry and melon smoothie

Image 10000000000001E3000001E2F8EE32AD.jpg

Photo credit: Thibaut Ruggeri.

69Serves 2

70Preparation time: 15 minutes

71Difficulty:

Image 10000000000000290000001D90074D6D.jpg

72Ingredients
3 vanilla yoghurts
100 g raspberries
50 g blueberries
200 g melon

73Place the raspberries, blueberries and the three vanilla yoghurts in a blender.

74Remove the seeds from the melon and peel it. Cut it into small cubes and add to the mixture.

75Start the blender, add one or two ice cubes, depending on the desired consistency.

76Serve chilled.

77Chef’s note

78This dessert covers almost half of the Dietary Reference Intake for vitamin C (40%). It also provides other elements that boost the immune system, including probiotics (yoghurt) and polyphenols (berries).

79Nutritional analysis per person

Energy (Cal)

Carbs (g)

255

41

Lipids (g)

Protein (g)

7

7

Notes

1 Drinking cranberry juice every day particularly helps to fight against recurrent urinary infections..

Auteurs

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