Chapter 22: Nutrition, Metabolism, and Temperature Regulation

NUTRITION

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.

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 (BER) includes your basal metabolic rate (BMR) and general daily activities

• For every Kg of body weight 1.3 Calories is required every hour. (An athlete weighing 50Kg would require 1.3 × 24hrs × 50Kg = 1560 Calories/day)
• For a calculation of your BMR, see the calculator on the Resting Daily Energy Expenditure (RDEE) page

Extra energy requirements (EER)

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

An athlete weighing 50Kg who trains for two hours would require an intake of approximately 2410 Calories (BER + EER = 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 Calories, Fats - 9 Calories and Protein - 4 Calories.

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

• Carbohydrates - 57% of 2410 = 1374 Calories - at 4 Calories/gram = 1374 ÷ 4 = 343 grams
• Fats - 30% of 2410 = 723 Calories - at 9 Calories/gram = 723 ÷ 9 = 80 grams
• Protein - 13% of 2410 = 313 Calories - at 4 Calories/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 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.

Unsaturated	Saturated
Sunflower oil	Beef
Olive Oil	Bacon
Rice Oil	Cheese
Nuts	Butter
Rapeseed Oil	Biscuits
Oily fish - Sardines	Crisps

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 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. Thestarchy 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

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.

Metabolism

Our bodies get the energy they need from food through metabolism, the chemical reactions in the body's cells that convert the fuel from food into the energy needed to do everything from moving to thinking to growing.

Specific proteins in the body control the chemical reactions of metabolism, and each chemical reaction is coordinated with other body functions. In fact, thousands of metabolic reactions happen at the same time — all regulated by the body — to keep our cells healthy and working.

Metabolism is a constant process that begins when we're conceived and ends when we die. It is a vital process for all life forms — not just humans. If metabolism stops, a living thing dies.

Here's an example of how the process of metabolism works in humans — and it begins with plants. First, a green plant takes in energy from sunlight. The plant uses this energy and the molecule chlorophyll (which gives plants their green color) to build sugars from water and carbon dioxide in a process known as photosynthesis.

When people and animals eat the plants (or, if they're carnivores, when they eat animals that have eaten the plants), they take in this energy (in the form of sugar), along with other vital cell-building chemicals.

The body's next step is to break the sugar down so that the energy released can be distributed to, and used as fuel by, the body's cells.

Enzymes

After food is eaten, molecules in the digestive system called enzymes break proteins down into amino acids, fats into fatty acids, and carbohydrates into simple sugars (for example, glucose). In addition to sugar, both amino acids and fatty acids can be used as energy sources by the body when needed. These compounds are absorbed into the blood, which transports them to the cells.

After they enter the cells, other enzymes act to speed up or regulate the chemical reactions involved with "metabolizing" these compounds. During these processes, the energy from these compounds can be released for use by the body or stored in body tissues, especially the liver, muscles, and body fat.

In this way, the process of metabolism is really a balancing act involving two kinds of activities that go on at the same time — the building up of body tissues and energy stores and the breaking down of body tissues and energy stores to generate more fuel for body functions:

• Anabolism, or constructive metabolism, is all about building and storing: It supports the growth of new cells, the maintenance of body tissues, and the storage of energy for use in the future. During anabolism, small molecules are changed into larger, more complex molecules of carbohydrate, protein, and fat.
• Catabolism, or destructive metabolism, is the process that produces the energy required for all activity in the cells. In this process, cells break down large molecules (mostly carbohydrates and fats) to release energy. This energy release provides fuel for anabolism, heats the body, and enables the muscles to contract and the body to move. As complex chemical units are broken down into more simple substances, the waste products released in the process of catabolism are removed from the body through the skin, kidneys, lungs, and intestines.

Temperature Regulation

The human body has the remarkable capacity for regulating its core temperature somewhere between 98°F and 100°F when the ambient temperature is between approximately 68°F and 130°F according to Guyton. This presumes a nude body and dry air. The external heat transfer mechanisms are radiation, conduction and convection and evaporation of perspiration. The process is far more than the passive operation of these heat transfer mechanisms, however. The body takes a very active role in temperature regulation.

The temperature of the body is regulated by neural feedback mechanisms which operate primarily through the hypothalmus. The hypothalmus contains not only the control mechanisms, but also the key temperature sensors. Under control of these mechanisms, sweating begins almost precisely at a skin temperature of 37°C and increases rapidly as the skin temperature rises above this value. The heat production of the body under these conditions remains almost constant as the skin temperature rises. If the skin temperature drops below 37°C a variety of responses are initiated to conserve the heat in the body and to increase heat production. These include

• Vasoconstriction to decrease the flow of heat to the skin.
• Cessation of sweating.
• Shivering to increase heat production in the muscles.
• Secretion of norepinephrine, epinephrine, and thyroxine to increase heat production
• In lower animals, the erection of the hairs and fur to increase insulation.