In the 1940's the Recommended Dietary Allowance guidelines were made to help the population meet the minimum food requirements for health.
Since then, the guidelines have been revised, and hundreds of research articles are published every year on nutrition and sports medicine.
Current research suggests that how much nutrition you require depends on your age, gender, body composition, and level of exercise, among other things.
Here are a few excerpts from recent guidelines from the international society of sports nutrition and exercise. See the link under references for the full article.
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).
Individuals engaged in a general fitness program and are not necessarily training to meet any type of performance goal can typically meet daily carbohydrate needs by consuming a normal diet (i.e., 45–55% CHO [3–5 g/kg/day], 15–20% PRO [0.8–1.2 g/kg/day], and 25–35% fat [0.5–1.5 g/kg/day]). However, athletes involved in moderate and high-volume training need greater amounts of carbohydrate and protein in their diet to meet macronutrient needs.
Preferably, the majority of dietary carbohydrate should come from whole grains, vegetables, fruits, etc. while foods that empty quickly from the stomach such as refined sugars, starches and engineered sports nutrition products should be reserved for situations in which glycogen resynthesis needs to occur at accelerated rates.
Considerable debate exists surrounding the amount of protein needed in an athlete’s diet. Initially, it was recommended that athletes do not need to ingest more than the RDA for protein (i.e., 0.8 to 1.0 g/kg/d for children, adolescents and adults). However, research spanning the past 30 years has indicated that athletes engaged in intense training may benefit from ingesting about two times the RDA of protein in their diet (1.4–1.8 g/kg/d) to maintain protein balance. If an insufficient amount of protein is consumed, an athlete will develop and maintain a negative nitrogen balance, indicating protein catabolism and slow recovery. Over time, this may lead to muscle wasting, injuries, illness, and training intolerance.
The dietary recommendations of fat intake for athletes are similar to or slightly greater than dietary recommendations made to non-athletes to promote health. Maintenance of energy balance, replenishment of intramuscular triacylglycerol stores and adequate consumption of essential fatty acids are important for athletes, and all serve as reasons for an increased intake of dietary fat. Depending upon the athlete’s training status or goals, the amount of dietary fat recommended for daily intake can change. For example, higher-fat diets appear to maintain circulating testosterone concentrations better than low-fat diets. Additionally, higher fat intakes may provide valuable translational evidence to the documented testosterone suppression which can occur during volume-type overtraining. Generally, it is recommended that athletes consume a moderate amount of fat (approximately 30% of their daily caloric intake), while proportions up to 50% of daily calories can be safely ingested by athletes during regular high-volume training. In situations where an athlete may be interested in reducing their body fat, dietary fat intakes ranging from 0.5 to 1 g/kg/day have been recommended results in situations where daily fat intake might comprise as little as 20% of total calories in the diet.