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Nutritional strategies to optimize your immune system

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Athletes engaged in heavy training programs, or in the final preparation for competition, appear more susceptible to infection than the general population. This increased susceptibility to infection arises because of an exercise or training-induced suppression of the immune system. Nutritional practices can help to maintain or improve immune function and limit the risk of illness compromising training and competitive performance.

Immune function suppression in athletes is always caused by multiple factors. For example, the risk of upper respiratory tract infections is increased after repeated cycles of unusually heavy exercise, exposure to novel pathogens, lack of sleep, severe mental stress, malnutrition, and weight loss4. Athletes often neglect many of these factors and only focus on supplements that claim to boost immune function.

A good diet improves the immune system

It is well known that diet can influence the immune system. The combination of a poor diet and exercise has even greater negative effects on the immune system. A negative energy balance means that at least one of the macronutrients must be deficient, which often results in micronutrient deficiencies.

Eat enough carbohydrates during, before, and after exercise

Especially carbohydrate availability has a great impact on exercise-induced immune changes. Exercising in a glycogen depleted state, or after some days on a low carbohydrate diet results in greater stress responses and depressed immune function. During periods of heavy training, athletes should eat sufficient carbohydrate to cover about 60% of their energy needs. This recommendation aims at restoring muscle and liver glycogen stores to ensure that there is enough carbohydrate available for muscle contraction for training on successive days.

It is also important to implement appropriate nutritional strategies before, during, and after exercise. Longer training sessions or events provide opportunities for athletes to ingest foods or drinks to maintain energy and fluid levels. During prolonged high intensity exercise, 30-60 grams of carbohydrates per hour in foods or drinks should attenuate various aspects of the immune function suppression2. A recovery snack after exercise, containing carbohydrates and proteins, also has positive effects on immune function.

Most athletes consume enough protein to keep them healthy

Proteins are involved in many aspects of the immune system. While protein deficiency impairs the immune system and increases susceptibility to infection, excessive protein intake may be detrimental to immune functions. The balance of amino acids in the free pool is affected by excessive consumption of individual amino acids. It increases the relative proportion of one amino acids and decreases the relative proportion of others.

Athletes who maintain a well balanced and varied diet will consume enough protein to keep them healthy. However, some endurance athletes or vegetarian athletes may fall short of their individual specific requirements.

Glutamine is a non-essential amino acid and is used as an energy substrate by many immune cells. Prolonged exercise depletes plasma concentrations of glutamine. The overtraining syndrome is also associated with chronic reduction in plasma glutamine concentrations. Supplementing athletes with glutamine can prevent the exercise-induced fall in plasma levels. However, glutamine supplements are unable to  prevent declines in immune system function despite being able to increase or maintain plasma glutamine concentrations.

Fats are also essential in a good diet

Excessive intake of fat can have negative health effects, especially saturated fats and trans fatty acids. Although, in the correct proportions, fats are an essential part of a healthy diet. For athletes, 20-30% of their energy intake should come from fats. A deficiency of essential fatty acids can result in deficiencies of lipid soluble micronutrients, such as vitamins A, D, E, and K.  

Antioxidants act as a natural defence mechanism

The human body uses antioxidants as a natural defence mechanism to counteract the possible detrimental effects of free radical production. They neutralise oxidants and thus reduce free radical formation.  Antioxidant deficiencies can have a negative effect on immunity in athletes. Although, excess intake doesn't lead to extra protection and might actually be detrimental. Recent studies suggest that excessive antioxidant consumption can also reduce the rate of performance improvement in response to endurance training. It is not recommended to take large doses of individual vitamins or antioxidant mixtures. For athletes it's better to obtain enough antioxidants from the consumption of fruits and vegetables.

Antioxidant nutrients include many vitamins and minerals, such as vitamin A, vitamin C, vitamin E, selenium, and copper. Deficiencies of these micronutrients are very unlikely if the diet is well balanced and varied.

Another antioxidant that had received a considerable amount of attention in sports and exercise is the bioflavonoid quercetin. Quercetin can be found in many foods, especially cherries, cranberries and apples. However, more research is needed to find the actual effects of quercetin on the immune system.

Recommendations

A well balanced and varied diet is very important to optimize your immune system. It is recommended to get all essential nutrients from food rather than in supplemental form because micronutrients are better available from food. Fruits and vegetables contain a lot of antioxidants. Your immune system will benefit more from adding some extra fruit or fruit- or vegetable juices to your diet than consuming expensive supplements. There is also no convincing evidence that supplements, including high doses of antioxidant vitamins, glutamine, zinc, probiotics and Echinacea, can prevent exercise-induced immune suppression2.

After exercise several factors can help to maximize recovery and minimize the risk of infection. These include:

  • - Managing training loads and daily physical activity
  • - Managing psychological stress
  • - Incorporate sufficient rest
  • - Ensure adequate sleep
  • - Minimize exposure to pathogens
  • - Have a well balanced diet providing enough fuel for training and recovery, and a good mix of nutrients and other food components3.

1. Davidson, G., & Simpson, R. J. (2011). Immunity. In S. A. Lanham-New, S. J. Stear, S. M. Shirrefs, & A. L. Collins, Sports and exercise nutrition (pp. 281-303). Wiley-Blackwell.

2. Gleeson, M., Nieman, D. C., & Pedersen, B. K. (2004). Exercise, nutrition and immune function. Journal of Sports Science , 22: 115-1225.

3. Pyne, D. B., Gleeson, M., McDonald, W., Clancy, R. L., Perry Jr, C., & Fricker, P. A. (2000). Training strategies to maintain immunocompetence in athletes. International Journal of Sports Medicine , 21: S51-60.

4. Walsh, N. P., Gleeson, M., Pyne, D. B., Nieman, D. C., Dhabhar, F. S., Shephard, R. J., et al. (2011). Position statement. Part two: Maintaining immune health. International Society of Exercise and Immunology , 17: 64-103.

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