15.5: Nutrients that are critical to athletes
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Physical activity requires energy and the type of activity, your body size, training and type of activity will determine your total daily energy expenditure. Obviously, non-exercise burns fewer calories and most people tend to spend more hours a day doing these types of activities than exercise. Tere are three energy macro nutrients as you have learned - carbohydrate, fat, and protein. Carbohydrate and fat are the preferred fuel sources. Both meal composition and timing relative to exercise are important for the athlete.
For athletes, an intake of more than 55% of calories from carbohydrate is recommended daily as carbohydrate is the preferred energy source. In some cases, athletes may carbohydrate load their muscles glycogen which may be useful for activities lasting more than 90 minutes. To carbohydrate load, one eats 7 -10 grams carbohydrate per kg body mass three days prior to the competitive event and after strenuous exercise that depletes the glycogen stores. Carbohydrate loading seems to work best in untrained people, not well-trained athletes and does not work in women. Recent scientific evidence suggests a better way to ensure adequate glycogen stores is to eat adequate amounts of carbohydrate (55% or greater) daily.
In the chapter on protein, you learned the RDA for protein is approximately 0.8 grams/kg body weight. Athletes need more protein (1.0 to 1.5 grams/kg/day or 10 to 15% of calories) but these levels may be less than they are currently consuming. The American diet generally contains more protein than required to build or maintain tissue. If carbohydrate is 55% or calories and protein is 10-15% of calories, then the remainder of the calories will be from fat (20-35%).
The timing of meals is important for the athlete. Any food should be eaten at least 30 minutes and best if 1-2 hours, before an event or workout. The foods selected should be rich in carbohydrates, low in fat, fiber, and protein. Within two hours after the event or workout, a post-meal should be eaten that is rich in carbohydrate to replace lost muscle glycogen, modest in protein to help rebuild used muscle and some fat.
Several minerals can be a concern for athletes. These minerals include calcium and iron. Weight bearing exercises will increase calcium retention in bones but many athletes avoid eating calcium rich foods like dairy so their calcium intake is inadequate. Depending on the type of exercise, iron deficiency can be a problem. a number of factors can contribute to this deficiency including inadequate iron intake, increased red blood breakdown, sweat loss and gastrointestinal damage that occurs in 8-23% of ultra-endurance athletes.
Vitamins are important for the athlete too but are generally not a concern with the athlete unless they are not eating a well-balanced diet such as that recommended by MyPlate.
Hydration is important for the athlete. Water is essential to keep the body cool and thirst is not a reliable indicator of our body's need for water during exercise. During exercise, athletes may sweat and this water and electrolyte losses need to be replaced. Sweat is composed of water, sodium chloride, iron, zinc, copper, potassium, calcium, magnesium and other trace minerals. Depending on the length of the event and the intensity of sweating, the athlete should drink water during the workout or competition. Sodium, potassium, and chloride may not need to be replaced too. Water, which does not contain electrolytes, or a carbohydrate/electrolyte drink may be an appropriate selection. The recommendation is 6-12 oz every 15-20 minutes. After approximately two cups of water, electrolytes should be consumed for every pound of body weight lost.
Consuming too much water can dilute blood sodium concentration resulting in hyponatremia, a condition that leads to neurological dysfunction and possible death. Excessive sweating can also cause hyponatremia.
Female Athlete Triad
Ballet, gymnastics, and women long distance running are three sports that suffer from the female athlete triad. This condition is very serious and is characterized by disordered eating behavior, amenorrhea (because body fat stores are too low), and osteoporosis (usually manifested as stress fractures). Female athlete triad requires a medical team specifically trained to diagnose and treat.