The most important nutritional component for athletes is actually adequate energy. Adequate energy, enough to counterbalance the expenditure, optimizes training and performance.
For People who participate in a general fitness program (e.g., exercising 30–40 min per day, 3 times per week), a typical diet (e.g., 1800–2400 kcals/day or about 25–35 kcals/kg/day for a 50–80 kg individual) can be just fine to meet their needs. That’s because their caloric demands from exercise are not too great (e.g., 200–400 kcals/session).
Athletes involved in moderate levels of intense training (e.g., 2–3 h per day of intense exercise performed 5–6 times per week) or high-volume intense training (e.g., 3–6 h per day of intense training in 1–2 workouts for 5– 6 days per week) may expend 600–1200 kcals or more per hour during exercise. Thus, their caloric needs may be as high as 40–70 kcals/kg/day (2000–7000 kcals/day for a 50–100 kg athlete).
For elite athletes, energy expenditure during heavy training or competition will further exceed these levels
Fact: energy expenditure for cyclists to compete in the Tour de France has been estimated as high as 12,000 kcals/day (150–200 kcals/kg/day for a 60–80 kg athlete)
Maintaining an energy deficient diet during training often leads to a number of physical (i.e., loss of fat-free mass, illness, reduced sleep quality, incomplete recovery, hormonal fluctuations, increased resting heart rate, etc.) and psychological (i.e., apathy towards training, heightened stress) adverse outcomes.
The high energy requirement is often difficult to be achieved because of the schedule of the athlete and often the gastrointestinal discomfort that may be an issue. Sports nutritionists’ have to create a personilised diet for each athlete depending on his needs. It is recommended that athletes consume four to six meals per day and snacks in between meals to meet energy needs. Due to practical concerns, the use of nutrient dense energy foods, energy bars and high calorie carbohydrate/protein supplements provides a convenient way for athletes to supplement their diet in order to maintain energy intake during training.
In conclusion each athlete has different needs depending on his sport, schedule, age, height and many more factors. A personalize diet plan by a specialized professional is recommended in order to ensure that the athlete has the best possible performance in both training and competitions at least from a nutritional point of view.
Kerksick, C. M., Wilborn, C. D., Roberts, M. D., Smith-Ryan, A., Kleiner, S. M., Jäger, R., Collins, R., Cooke, M., Davis, J. N., Galvan, E., Greenwood, M., Lowery, L. M., Wildman, R., Antonio, J., & Kreider, R. B. (2018). ISSN exercise & sports nutrition review update: research & recommendations. Journal of the International Society of Sports Nutrition, 15(1), 38. https://doi.org/10.1186/s12970-018-0242-y