NUTRITION AND SPORTS. MACRONUTRIENTS
Carbohydrates
The first source of energy used during physical comes from the glucose resulting from the break-up of muscle glycogen. However, glycogen stored in muscles only produces glucose for a few hours during moderate physical exercise.
After the glycogen from muscles is used up, glucose must be provided through the glycogen in the liver (through the process of glycogenolysis) and the transformation of other immediate compounds into glucose (through glycogenesis).
If glycogen stores in muscle and liver are insufficient, the sportsman reaches his “maximum", which can occur during the actual competition event or after a few days of strong training. At that time, the sportsman feels fatigued and his physical performance decreases.
In order to reach a status of maximum accumulation of glycogen, sportsmen who train more than 90 minutes per day need 8 to 10 mg of carbohydrates per kg/body weight. This means that 60-70% of the total calories in the diet must be in the form carbohydrates for resistance or endurance sports and 50-55% for velocity and strength sports.
After a sporting event, replacement of glycogen levels may take from 12 to 48 hours (although 60% of the replacement occurs in the first few hours). This is why the intake of carbohydrates after a sporting event or training session is very important. Sportsmen should consume 100 g of carbohydrates during the first 30 minutes after exercise, with 100 additional grams every 2 to 4 hours thereafter.
The carbohydrates to be consumed by sportsmen must be evaluated according to the glycaemic index (speed of absorption and utilisation/storage). Carbohydrates with a high glycaemic index are immediately available for utilisation and are the best source of carbohydrates during and after physical exervise.
Fats
Fat is a less preferred fuelling source than carbohydrates but because fat is readily available in fat tissues it is the best source of energy to endure long-lasting events. Fats are used in the liver once the energy from glycogen is used up. Moreover, fats in the diet contribute to the delivery of liposoluble vitamins.
Nonetheless, sport men should not be encouraged to take large amounts of fats. A diet that contains 25-30% of the total calories in the form of fats is recommended (sportsmen in resistance training can take up to 35%). Two fifths (2/5) of the total fat ingested should be of vegetal origin.
Proteins
Unlike carbohydrates and lipids, proteins play a structural role. However, when glycogen stores are depleted and fat reserves limited, they can account for up to 20% of the energy source.
Even though it has been assumed that the protein needs of sportsmen should take up a significant percentage of the diet, a number of dietician and nutrition specialists do not support this thesis.
Las necesidades requeridas, para mantener un adecuado tono y capacidad muscular, equilibrar las pérdidas naturales y debido a la poca eficiencia de utilización de las proteínas (para su metabolismo es necesario un gasto energético por el organismo), se ha calculado que deben suponer un 12-15% de las calorías de la dieta. Dicha cantidad corresponde, un varón adulto deportista, un mínimo de 1.5 g/Kg de peso.