Energy intake and expenditure Essay
Energy is needed by the body to stay alive, grow, keep warm and move around. Energy is provided by food and drink. It comes from the fat, carbohydrate, protein and alcohol the diet contains. Energy requirements vary from one individual to the next, depending on factors such as age, sex, body composition and physical activity level. Energy expenditure is the sum of the basal metabolic rate (the amount of energy expended while at complete rest), the thermic effect of food (TEF, the energy required to digest and absorb food) and the energy expended in physical activity.
To maintain body weight, it is necessary to balance the energy derived from food with that expended in physical activity. To lose weight, energy expenditure must exceed intake, and to gain weight, energy intake must exceed expenditure.
Meeting energy needs is the first nutritional priority for athletes. A healthy diet contains the right proportions of carbohydrate (CHO), fat, protein, vitamins and minerals. Carbohydrates and fats are the major sources of energy although energy can be obtained from protein.
Energy is measured in Kilocalories (kcal) or Kilojoules (kJ): 1kcal = 4.2 kJ. 1g of Carbohydrates contains 3.75 kcal (16kJ)
1g of Fat contains 9 kcal (37kJ)
1g of Protein contains 4 kcal (17 kJ)
The amount of food we eat (energy intake) should match energy expenditure. If this is the case then we should neither gain nor lose weight as we are in energy balance. If there is inadequate energy intake relative to energy expenditure, the body will use fat and lean tissue mass for fuel. Loss of muscle results in reductions in strength and endurance capacity. Total daily energy expenditure is influenced by heredity, age, sex, body size, fat-free mass, environmental factors, pregnancy and the intensity, frequency and duration of exercise. It is generally made up of three components:
1. Resting Metabolic Rate. This is divided into Basal Metabolic rate (BMR) which is the minimum energy requirement to sustain the body’s functions in the waking state and Sleeping Metabolic Rate.
2. The thermic effect of food intake (TEF) which is the energy expended on digestion, absorption, and storage of foods – amounts to about 10% of daily energy intake.
3. The energy (thermic) cost of exercise (TEE) includes normal everyday activities as well as the energy cost of football training and matches. The BMR demands around two-thirds of our daily energy intake required for normal everyday activities and is the largest part of our daily energy expenditure.
Body mass, statue and age or estimates of fat-free body mass provide accurate estimates of BMR. The following equation can be used to calculate BMR for people aged between 18-30. Energy intake and expenditure are expressed in Kilocalories (kcal) and Body Weight in Kilograms is represented by W. Males: BMR (kcal or kJ/24 h) = 17.5 X W + 651
Females: BMR (kcal or kJ/24 h) = 14.7 X W + 496
According to various studies, a man around 25 years of age with a sedentary lifestyle is recommended to consume around 2500 kcal whereas a man of a similar age who is very active should consume about 3333 kcal. Older people are recommended to have a lower intake than younger people and males generally have a higher intake than females.
Studies on elite football players show that the energy intake is likely to be 2033 – 4000 kcal (8500 – 16500 kJ) per day, although this depends on factors such as intensive training where intake may need to be increased or periods of inactivity such as injury where the player should reduce intake. Variations in energy intake are likely to lead to weight loss or gain. Elite players have been found to have diets which are too high in fat and too low in CHO intake. They should be encouraged to consume more unsaturated fat (e.g. margarine) instead of saturated fat (e.g. butter) as well as complex carbohydrates such as pasta and rice. So what are the respective amounts of CHO, fat, and protein required for a player with a daily intake of 16000 kJ or 3809 kcal. Firstly, for a standard healthy diet, general dietary recommendations of 55-60% CHO, 25-30% Fat and 10-15% protein are advised.
A simple calculation shows that the player should be consuming 550-600g of CHO, 108-130g of fat and 94-141g of protein. CHO Intake = 55-60% of 16000 kJ (Energy intake) / 16 kJ (energy in 1g of CHO) = 550-600g Fat Intake = 25-30% of 16000 kJ (Energy intake) / 37kJ (energy in 1g of Fat) = 108-130g Protein Intake = 10-15% of 16000 kJ (Energy intake) / 17 kJ (energy in 1g of Protein) = 94-141g Players can evaluate their energy balance through recording their own weight. Any changes in weight may indicate a diet that is either lacking or too excessive. However, players can positively gain some weight due to increased muscle mass from weight training and an examination of body composition (such as skinfold measurement) may be a better indicator the stability of body weight. Players may also weight and record all the food and drink they consume and food labels supply valuable information on what food contains and how many calories.