Nutrition and Overtraining, Is There a Connection?

Completing a workout inevitably stresses the body by disrupting the normal balance of the body (homeostasis). With proper workout planning, carefully timed load progression, and sufficient rest, these disruptive moments are beneficial for the development of adaptations at the cellular, tissue, and functional levels. They enhance physical ability and performance. However, long-term overuse may undermine this adaptation process and lead to overtraining syndrome.


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This condition is defined as a marked decrease in performance despite rigorous training, systemic fatigue, a weakened immune system, mood disturbances, sleep disorders, gastrointestinal disorders, altered blood chemistry, and changes in physiological parameters such as resting heartbeat. However, overtraining is not always caused by excessive amounts of training. It is the sum of all stressors facing the body that eventually lead to development of this syndrome.

Performance stress, surroundings, fellow athletes and work-related factors are some of the elements to be taken into account beyond the training load. At this level, poor or imbalanced nutritional intake can also be a contributing factor to the overall stress that affects the body. In fact, nutritional intake as a whole is involved in the various adaptive and recovery processes of the body. Therefore, a poorly balanced diet will cause the recovery process and a return to homeostasis to be slower.  With regard to intensive training, a longer than expected recovery period may result in the appearance of overtraining symptoms. It is important to mention that insufficient nutritional intake can also lead to Relative Energy Deficiency in Sport, a condition that also results in numerous metabolic changes and decreased performance. These concepts are closely related to one another and always lead to a breakdown in the body's proper functioning. An extended period of rest (sometimes several months) is then necessary to allow the body to recover.  


In order to limit the risk of developing an overtraining syndrome, it is important to ensure that the stress load on the body is well planned. From a nutritional standpoint, an insufficient intake of carbohydrates may be a factor that contributes to fatigue and poor performance associated with overtraining syndrome. Decreased glycogen stores in the muscles, not offset by adequate dietary intake, would cause an alteration in the body's hormonal response, among other things (increased release of catecholamines, cortisol and glucagon). Also, it is well established that performing a workout with low carbohydrate availability speeds up the onset of fatigue. In a situation where these reserves are not being replenished after training, this leads to a prolonged recovery period between sessions. Therefore, it is important to adjust one's daily carbohydrate intake according to the training load.


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Another aspect related to the development of overtraining syndrome is an out-of-control increase in oxidative stress. Among overtrained athletes, there is an increase in resting oxidative stress markers when compared to a control group. Furthermore, these markers also increase with exercise. When oxidative stress becomes pathological, the excess free radicals produced by the body can cause inflammation, muscle fatigue and pain. The end result is a decrease in performance.   

Despite the fact that it is unclear whether the increase in oxidative stress markers causes or is the result of overtraining, it is important to establish dietary habits that will be conducive to the proper regulation of the body's antioxidant capacity. Consequently, for athletes, it is essential to ensure that their antioxidant needs are adequately met through diet. Vitamins A, C and E as well as zinc, selenium, copper, manganese and polyphenols are all essential nutritional components that enable the body to adequately fight oxidative stress. A diet rich in vegetables, fruits, whole grains, nuts and seeds will help provide all of these essential nutrients. Be careful though! Taking antioxidants in the form of excessive supplements could, on the contrary, have a negative effect on the body and the development of adaptations as a result of working out. It is better to derive your antioxidants from dietary intake than to consume them as supplements.


Maintaining an adequate intake of essential fatty acids, especially from the omega-3 family, should also be encouraged in athletes. This is because they are exposed to acute and chronic stress as a result of their training. This compromises both their immune system and antioxidant defences. Fatty acid composition from their diet can produce significant immune and inflammatory buffering effects, particularly in the expression and production of cytokines.

Sufficient intake of omega-3 fatty acids will therefore optimize the body's inflammatory response. As a result, inflammatory stress caused by intensive training will be better managed by the body. In practice, regularly consuming oily fish such as salmon or sardines combined with the daily consumption of walnuts, chia seeds or flaxseed, as well as the use of canola oil or first cold-pressed camelina, will lead to a favourable increase in dietary intake of omega-3.


Ultimately, overtraining syndrome appears to be the body's overall response to an excessive accumulation of stressors. While diet is not the only factor that leads to the development of this syndrome, it is important to be aware of its role in the prevention and management of this condition. A well-balanced diet that meets all the nutritional needs of an athlete will allow him to cope more effectively with the various stresses brought on by training. With proper planning of the training load and an appropriate dietary intake, the athlete will have a better chance of responding favourably to the various metabolic disturbances that are triggered by his training and will therefore develop physiological adaptations that are conducive to long-term performance.


Main References:

  • Halson, S.L. & Jeukendrup, A.E. (2004). Does Overtraining Exist?: An Analysis of Overreaching and Overtraining Research. Sports Medicine, 34(14), 967‑981.
  • Kreher, J.B. & Schwartz, J.B. (2012). Overtraining Syndrome: A Practical Guide. Sports Health: A Multidisciplinary Approach, 4(2), 128‑138.
  • Meeusen, R. et al. (2013). Prevention, Diagnosis, and Treatment of the Overtraining Syndrome: Joint Consensus Statement of the European College of Sport Science and the American College of Sports Medicine. Medicine & Science in Sports & Exercise, 45(1), 186‑205.

Isabelle Morin

Nutritionnist at The Running Clinic