Jennifer Ellison-Brown: Nutrition for health and performance
To be healthy and able to perform well in sports needs a balanced diet for energy, repair, growth and good health.
Food contains the basic materials and a balance and varied diet contains seven essential components: carbohydrates, fats, proteins, vitamins, minerals, fibres and water.
The main food types that supply energy should be in the greatest proportion.
The body needs energy to keep the systems going. This is called our basal metabolic rate. It is the amount of energy we need to keep alive and healthy and is affected by age, sex, body size and body composition.
The body also needs energy for physical activities. The energy needed depends on the type of activity or sport involved; age, sex and workload will affect the required energy level.
Energy is measured in kilo calories or kilo joules. All food contains an energy value, which is usually calculated as the number of kilo joules per gramme of food. Therefore, exercise is measured by the number of kilo joules used per hour.
The amount of energy in the food depends on the amount of carbohydrates, proteins and fats it contains. The amount of energy needed depends on the intensity of the activity. When we work hard, the energy we use comes from our store of glycogen, which is made from carbohydrates and fats that are stored in the muscles and in the liver.
Glycogen breaks down to glucose, which is used with oxygen (anaerobic) or without oxygen (anaerobic) to release energy.
For aerobic activities that involve relatively low intensity over a long span of time e.g., endurance running the glucose and fat are oxidised with oxygen to release much energy (fats can only burn in the flames of carbs).
However, anaerobic activities which involves high intensity e.g., short sprints doesn't give the body a chance to supply oxygen to the muscles fast enough for the aerobic breakdown of glucose and fats. Therefore, the muscles have to work without oxygen. Only glucose can be broken down without oxygen, therefore the glucose and glycogen store which releases glucose are rapidly used up.
Nutrition for sports
An athlete will 'carbo load'(carbohydrate loading) by eating extra carbohydrates to build supplies of glycogen, at the same time reducing the level of physical activity for at least three days before competition, to have enough energy for long-endurance events.
If the 'best' diet possible is eating, sport performance will gain an edge. The three-time phases we need to be aware of are:
Pre-event: This meal should be eaten with plenty of time for digestion, at least three-four hours before and should consist of carbohydrates e.g., bread, cereal and fruits to give slow, steady release of energy. Simple sugars, and food high in fat and protein, should be avoided. Include fluids to avoid dehydration.
During the event: Drink water in small sips and glucose-based drink if the activity lasts for more than one hour.
Post-event: Get a carbohydrate-rich snack as quickly as possible after an endurance event or tournament is over. The post-event meal should aim to replace the stock of glycogen that has been used up during the activity and continue to replace up to a day or two after. Carbohydrates, along with vitamins, minerals and some protein, must be included to help the body repair itself and restore all nutrients used. Plenty fluid intake must be included.
Fluid replacement: Only plain water is needed before and during activities lasting 60 minutes or less. Sport drink of glucose and electrolytes (sodium, potassium and magnesium) are encouraged after high-intensity activity that goes beyond 60 minutes. This will help to restore lost fluids, energy and minerals.
Next week: Issues related to PE and sports.