For every physical activity, the body requires energy and the amount depends on the duration and type of activity. Energy is measured in kcal 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.

Nutrient Balance

Carefully planned nutrition must provide an energy balance and a nutrient balance.

The nutrients are:

Proteins - essential to growth and repair of muscle and other body tissues
Fats - one source of energy and important in relation to fat soluble vitamins
Carbohydrates - our main source of energy
Minerals - those inorganic elements occurring in the body and which are critical to its normal functions
Vitamins - water and fat soluble vitamins play important roles in many chemical processes in the body
Water - essential to normal body function - as a vehicle for carrying other nutrients and because 60% of the human body is water
Roughage - the fibrous indigestible portion of our diet essential to health of the digestive system

Energy Fuel

Like fuel for a car, the energy we need has to be blended. The blend that we require is as follows:

57% Carbohydrates (sugar, sweets, bread, cakes)
30% Fats (dairy products, oil)
13% Protein (eggs, milk, meat, poultry, fish)

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.

As far as your body is concerned, there are two different types of amino acids: essential and non-essential. Non-essential amino acids are amino acids that your body can create out of other chemicals found in your body. Essential amino acids cannot be created, and therefore the only way to get them is through food.

Protein in our diets comes from both animal and vegetable sources.Most animal sources (meat, milk, eggs) provide what's called "complete protein," meaning that they contain all of the essential amino acids. Vegetable sources usually are low on or missing certain essential amino acids. For example, rice is low in isoleucine and lysine. However, different vegetable sources are deficient in different amino acids, and by combining different foods you can get all of the essential amino acids throughout the course of the day. Some vegetable sources contain quite a bit of protein - things like nuts and beans are all high in protein. By combining them you can get a complete range of the essential amino acids.

The RDA (recommended daily allowance) for protein is 0.36 grams of protein per pound of body weight. However, protein expert Dr. Peter Lemon recently concluded that exercise more than doubles your need for protein. Based on his review of the research, Lemon reports that if you're exercising on a regular basis, you'll need to consume at least 1.7 grams of protein per kilogram of bodyweight. For people who want to build muscle as fast as possible, this figure should be nearer 2.5 grams per kilogram of bodyweight.