Nutrition

Introduction

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

What are the daily energy requirements ?

Personal energy requirement = basic energy requirements + extra energy requirements

Basic energy requirements

• For every Kg of body weight 1.3 kcal is required every hour. (An athlete weighing 50Kg would require 1.3 * 24hrs * 50Kg = 1560 kcal/day)

Extra energy requirements

• For each hours training you require 8.5 kcal for each Kg of body weight. (For a two hour training session our 50Kg athlete would require 8.5 * 2hrs * 50Kg = 850 kcal)

An athlete weighing 50Kg who trains for two hours would require an intake of approx. 2410 kcal (1560 + 850)

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 energy yield per gram is as follows : Carbohydrate - 4 kcal, Fats - 9 kcal and Protein - 4 kcal. (Note: 1 calorie = 1 Kcal)

What does a 50 kg athlete require in terms of carbohydrates, fats and protein ?

• Carbohydrates - 57% of 2410 = 1374 kcal - at 4 kcal per gram = 1374 / 4 = 343 grams
• Fats - 30% of 2410 = 723 kcal - at 9 kcal per gram = 723 / 9 = 80 grams
• Protein - 13% of 2410 = 313 kcal - at 4 kcal per gram = 313 / 4 = 78 grams

Our 50kg athlete requires: 343 grams of Carbohydrates, 80 grams of Fat and 78 grams of Protein

What types of fat are there ?

The nature of the fat depends on the type of fatty acids which 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. As a rough guide 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 which contains a high percentage of saturated fatty acids.

What types of carbohydrates are there ?

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 these food stuffs 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 the your plate filled with carbohydrates and small amounts of protein such as meat, poultry and fish. The extra protein & vitamins you need will be in the starchy carbohydrates.

Carbohydrates for Performance

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 foods Glycaemic Index (GI) and the faster and higher the blood glucose rises the higher the GI. 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. There are times when it is beneficial to consume lower GI carbohydrates which are absorbed slowly over a longer period of time (2-4 hours before exercise). 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? And 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.

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.

Free Calculator and Diet Plan

• Calorie Calculator - a free Microsoft Excel 97 spreadsheet which you can download and use on your computer.
• Diet Plan - a free Microsoft Excel 97 spreadsheet which you can download and use on your computer.