For every physical activity, the body requires energy, and the amount depends on the duration and type of activity. Energy is measured in Calories and is obtained from the body stores or the food we eat. Glycogen is the primary fuel source used by the muscles to enable you to undertake both aerobic and anaerobic exercise. If you train with low glycogen stores, you will feel constantly tired, training performance will be lower, and you will be more prone to injury and illness.
A calorie (cal) is the amount of heat energy required to raise the temperature of 1g of water 1°C from 14° to 15°C. A kilocalorie (kcal) is the amount of heat required to raise the temperature of 1000g of water 1°C.
Carefully planned nutrition must provide an energy balance and a nutrient balance.
The nutrients are:
Personal energy requirement = basic energy requirements + extra energy requirements
Basic energy requirements (BER) include your basal metabolic rate (BMR) and daily activities.
Extra energy requirements (EER)
An athlete weighing 60Kg who trains for two hours would require an intake of approximately 2941 Calories (BER + EER = 1921 + 1020)
Like fuel for a car, the energy we need must be blended. The Dietary Guidelines for Americans  recommends the following blend:
For the following examples and calculations, I will use the following values: Fat 27%, Carbohydrate 52% and Protein 21%
The approximate energy yield per gram is as follows: Carbohydrate - 4.2 Calories, Fats - 9.5 Calories and Protein - 4.1 Calories.
What does a 60 kg athlete require in carbohydrates, fats and protein?
Our 60kg athlete requires 364 grams of Carbohydrates, 84 grams of Fat and 151 grams of Protein.
The nature of the fat depends on the type of fatty acids that make up the triglycerides. All fats contain saturated and unsaturated fatty acids but are usually described as 'saturated' or 'unsaturated' according to the proportion of fatty acids present. Saturated fats are generally solid at room temperature and tend to be animal fats. Unsaturated fats are liquid at room temperature and are usually vegetable fats. There are exceptions, e.g. palm oil, a vegetable oil containing a high percentage of saturated fatty acids.
There are two carbohydrates - starchy (complex) carbohydrates and simple sugars. The simple sugars are found in confectionery, muesli bars, cakes and biscuits, cereals, puddings, soft drinks and juices, jam and honey, but they also contain fat. Starchy carbohydrates are found in potatoes, rice, bread, whole grain cereals, semi-skimmed milk, yoghurt, fruit, vegetables, beans and pulses. Both types effectively replace muscle glycogen. Starchy carbohydrates are the ones that have all the vitamins and minerals in them as well as protein. They are also low in fat if you do not slap on loads of butter and fatty sauces. Starchy foods are much bulkier, so there can be a problem in eating that amount of food, so supplementing simple sugar alternatives is necessary.
Your digestive system converts the carbohydrates in food into glucose, a form of sugar carried in the blood and transported to cells for energy. In turn, the glucose is broken down into carbon dioxide and water. Any glucose not used by the cells is converted into glycogen - another carbohydrate stored in the muscles and liver. However, the body's glycogen capacity is limited to about 350 grams; once this maximum has been reached, excess glucose is quickly converted into fat. Base your main meal with the bulk on your plate filled with carbohydrates and small amounts of protein such as meat, poultry and fish. The extra protein & vitamins you may require will be in the starchy carbohydrates.
Lactose intolerance results when the mucosal cells of the small intestine fail to produce lactase which is essential for the digestion of lactose. Symptoms include diarrhoea, bloating, and abdominal cramps after consumption of milk or dairy products.
Carbohydrates for Performance
To support a training session or competition, athletes must eat at an appropriate time to absorb all the food, and their glycogen stores are fully replenished.
Following training & competition, an athlete's glycogen stores are depleted. To replenish them, the athlete needs to consider how carbohydrate is converted into blood glucose and transported to the muscles. The rapid replenishment of glycogen stores is vital for the track athlete with many races in a meeting.
The rise in blood glucose levels is indicated by a food's Glycaemic Index (GI) - the faster and higher the blood glucose rises, the higher the GI.
High GI foods take 1 to 2 hours to be absorbed, and low GI foods can take 3 to 4 hours.
Studies have shown that consuming high GI carbohydrates (approximately 1grm per kg body) within 2 hours after exercise speeds up the replenishment of glycogen stores and speeds up recovery time.
Glycogen stores will last for approximately 10 to 12 hours when at rest (sleeping), so this is why breakfast is essential.
Eating 5-6 meals or snacks daily will help maximise glycogen stores and energy levels, minimise fat storage and stabilise blood glucose and insulin levels.
Eating and Competition
What you eat on a day-to-day basis is extremely important for training. Your diet will affect how fast and well you progress and how soon you reach a competitive standard. The Nutritional Tips page provides some general nutritional advice to help you manage weight and body fat.
Once you are ready to compete, you will have a new concern: your competition diet. Is it important? What should you eat before your competition? When is the best time to eat? How much should you eat? Should you be eating during the event? Also, what can you eat between heats or matches? Much research has been done in this area, and specific dietary approaches can enhance competition performance.
What do I need to do?
Calculate your daily basic and extra requirements, monitor your daily intake (especially your carbohydrates) and then adjust your diet to meet your daily requirements. A well-balanced diet should provide you with the required nutrients but it needs to be monitored. The simplest way to monitor the 'energy balance' is to check your weight regularly.
Key factors in your training diet
Each day has three main meals and two to three snacks. All meals should contain carbohydrates and protein - 20 to 30 grams of protein with each main meal and 10 to 20 grams with each snack.
Have 1grm of carbohydrate per kg of body weight and about 30 grams of protein. The amount of carbohydrates will vary greatly, mainly depending on your workload. It may be in the region of 40 to 60 grams for main meals and 20 to 30 grams for snacks. The recovery meal is critical if you are training hard and possibly doing multiple daily sessions. Have a drink (e.g. a recovery drink or a pint of skimmed milk) and a banana immediately post-training (this provides about 10 grams of protein and 30 grams of carbohydrate), followed within about 45 minutes with more substantial food such as beans on toast and tuna.
Always try to eat at least five pieces of fruit per day. Skimmed milk is a high protein food and provides critical minerals, such as calcium and phosphorous.
Food Composition Tables
Food composition tables are widely used to assess nutrient and energy intakes and plan meals. The composition of a food can vary widely, depending, among other factors, on the variety of plant or animal, on growing and feeding conditions and, for some foods, on freshness. Tables are based on average values from several samples analysed in the laboratory and only provide a rough guide.
What do I need to do?
Calculate your daily basic and extra requirements, monitor your daily intake (especially your carbohydrates) and then adjust your diet to meet your daily requirements. A well-balanced diet should provide you with the required nutrients but it needs to be monitored. The simplest way to monitor the 'energy balance' is to check your weight regularly. If you are struggling, seek out someone with a sports Science and Nutrition degree or a recognised nutrition certification.
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