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 main source of fuel 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) includes your basal metabolic rate (BMR) and general 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 has to be blended. The Dietary Guidelines for Americans  recommends the following blend:
For the purposes of 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 terms of 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 both 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 that contains a high percentage of saturated fatty acids.
There are two types of carbohydrates - starchy (complex) carbohydrates and simple sugars. The simple sugar's are found in confectionery, muesli bars, cakes and biscuits, cereals, puddings, soft drinks and juices and jam and honey but they also contain fat. Starchy carbohydrates are found in potatoes, rice, bread, wholegrain cereals, semi skimmed milk, yoghurt, fruit, vegetables, beans and pulses. Both types effectively replace muscle glycogen. The starchy carbohydrates are the ones that have all the vitamins and minerals in them as well as protein. They are also low in fat as long as you do not slap on loads of butter and fatty sauces. The starchy foods are much more bulky so there can be a problem in actually eating that amount of food so supplementing with 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. The glucose, in turn, is broken down into carbon dioxide and water. Any glucose not used by the cells is converted into glycogen - another form of carbohydrate that is stored in the muscles and liver. However, the body's glycogen capacity is limited to about 350 grams; once this maximum has been reached, any 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 that is essential for the digestion of lactose. Symptoms include diarrhoea, bloating, and abdominal cramps following consumption of milk or dairy products.
Carbohydrates for Performance
To support a training session or competition athletes need to eat at an appropriate time so that all the food has been absorbed and their glycogen stores are fully replenished.
Following training & competition, an athlete's glycogen stores are depleted. In order to replenish them the athlete needs to consider the speed at which carbohydrate is converted into blood glucose and transported to the muscles. The rapid replenishment of glycogen stores is important for the track athlete who has a number of 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 to be absorbed.
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 therefore 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 a day, 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 how well you progress, and how soon you reach competitive standard. The page on Nutritional Tips provides some general nutritional advice to help you manage your 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? In addition, what can you eat between heats or matches? A lot of research has been done in this area, and it is clear that certain 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 good balanced diet should provide you with the required nutrients but does needs to be monitored. The simplest way to monitor the 'energy balance' is to keep a regular check of your weight.
Key factors in your training diet
Each day have three main meals and two to three snacks. All meals should contain both carbohydrate and protein - 20 to 30 grams worth of protein with each main meal and 10 to 20 grams with each snack.
The amount of carbohydrate 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. If you are training hard and possibly doing multiple daily sessions, the recovery meal is critical. Have 1grm of carbohydrate per kg of body weight and about 30 grams of protein. 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 great 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 to plan meals. The composition of 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 a number of samples analysed in the laboratory and therefore only provide a rough guide.
The following references provide additional information on this topic:
The reference for this page is:
The following Sports Coach pages provide additional information on this topic: