Kerksick et al. Journal of the International Society of Sports Nutrition (2018) 15:38
General dietary guidelines for active individuals
Individuals engaged in a general fitness program and are not necessarily training to meet any type of performance goal can typically meet daily needs by consuming a normal diet.
45–55% CHO [3– 5 g/kg/day],
15–20% PRO [0.8–1.2 g/kg/day],
25–35% fat [0.5–1.5 g/kg/day]).
A well-designed diet that meets energy intake needs and incorporates proper timing of nutrients is the foundation upon which a good training program can be developed.
Research has clearly shown that lacking sufficient calories and/or enough of the right type of macronutrients may impede an athlete’s training adaptations, while athletes who consume a balanced diet that meets energy needs can augment physiological training adaptations.
Moreover, maintaining an energy deficient diet during training may lead to loss of muscle mass, strength, and bone mineral density in addition to an increased susceptibility to illness and injuries, disturbances in immune, endocrine and reproductive function, and an increased prevalence of overreaching and/or overtraining.
Incorporating good dietary practices as part of a training program is one way to help optimize training
The primary component to optimize training and performance through nutrition is to ensure the athlete is consuming enough calories to offset energy expenditure. People who participate in a general fitness program (e.g., exercising 30–40 min per day, 3 times per week) can typically meet nutritional needs following a normal diet (e.g., 1800–2400 kcals/day or about 25–35 kcals/kg/day for a 50–80 kg individual) because their caloric demands from exercise are not too great (e.g., 200–400 kcals/session). However, 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.
For this reason, their caloric needs may approach 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. For example, 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).
Additionally it is difficult to consume enough food and maintain gastrointestinal comfort to train or race at peak levels. 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.
Nutritional analyses of athletes’ diets have revealed that many are susceptible to maintaining negative energy intakes during training. It is still a question whether there may be specific individualized occasions when negative energy balance may enhance performance in the days prior to running performance. Populations susceptible to negative energy balance include runners, cyclists, swimmers, triathletes, gymnasts, skaters, dancers, wrestlers, boxers, and athletes attempting to lose weight too quickly.
This means that care should be taken to plan meal times in concert with training, as well as to make sure athletes have sufficient availability of nutrient dense foods throughout the day for snacking between meals (e.g., fluids, carbohydrate/protein-rich foods and supplemental bars, etc.). For this reason, sports nutritionists’ often recommend that athletes consume four to six meals per day and snacks in between meals to meet energy needs. Due to these 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.