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Energy Energy Presentation Transcript

  • The Need for Energy
    • We obtain our energy from the food and drink that we consume in particular from CARBOHYDRATES , PROTEINS and FATS (lipids)
    • The energy in food is stored as potential energy, which is released during respiration and used to synthesise ATP in cells
    • The energy content of food can be measured in either kilojoules (kJ) or kilocalories (kcal)
  • Energy Balance
    • ENERGY IN - ENERGY OUT = CHANGE IN ENERGY STORES
    • [ When energy in - energy out = 0, the individual is in energy balance]
    • There are strong links between DIET , CORONARY HEART DISEASE and OBESITY
    • Current guidelines for our energy intake =
    50% Carbohydrate 20% Protein 30% Fat
  • Basal Metabolic Rate (BMR)
    • Your BASAL METABOLIC RATE , or BMR , is the minimum energy requirement needed to sustain life during a given peroid of time in a resting individual
    • BMR usually measured in MJ/day or kcal/day
    • BMR can be responsible for burning up to 70% of the total calories expended [for bodily processes], but this figure varies due to different factors
    • Obviously the body will burn more calories on top of those burned due to BMR
  • Factors affecting BMR
    • BMR will steadily decrease as we grow older as lean body mass decreases. As lean muscle tissue burns more energy per gram than fat, the greater the proportion of muscle to fat tissue on the body, the higher the BMR
    • Thus BMR can be increased by undertaking regular exercise
    • A person's height is also a factor, a tall thin person will have a higher BMR than a shorter, fatter person
    • BMR will increase in pregnant women
    • Short term factors such as a fever, high levels of stress hormones in the body and changes in the environmental temperature will result in an increase in BMR
    • Fasting, starving or malnutrition all result in a lowering of BMR. i.e. dieting alone will not be as effective as dieting and increased exercise . The negative effect of dieting on BMR can be offset with a positive effect from increased exercise
  • Thermogenesis [Heat Production]
    • Every time you eat, some energy is used up in DIGESTING, ABSORBING, METABOLISING and STORING the food. This energy is eventually converted to heat [ DIETARY-INDUCED THERMOGENESIS ]
    • However different types of food have different thermic effects:
          • PROTEIN : up to 17% of its energy can be burned off as heat
          • CARBOHYDRATES : about 10% is used to produce heat
          • FATS have the least thermic effect of all, only about 3%
    • Thus eating carbohydrate and protein rich foods increases energy expenditure much more than eating high fat foods. Apart from the other health reasons previously discussed, this is another good reason to keep your intake of fat low
    • Every time you eat, thermogenesis increases, therefore increasing the number of times you eat, without increasing the daily calorie intake, will increase the amount of energy used to digest and metabolise the food.
    LOW HIGH
  • Energy Expenditure
    • How much energy we need on a day to day basis depends on factors such as:
      • Body Size
      • Body Composition
      • Age
      • Sex
      • Nutritional status
      • Pregnancy & Breast Feeding
      • Activity
      • Climate
  • Measurement of Energy Expenditure
    • There are several methods which can be used to measure energy expenditure:
        • DIRECT CALORIMETRY
        • INDIRECT CALORIMETRY
        • HEART RATE RECORDING
  • Direct Calorimetry
    • Since all energy is eventually converted to heat energy, the total energy expended by an individual can be measured DIRECTLY by measuring the heat energy produced
    • This involves placing the individual inside an insulated chamber and directly measuring the temperature rise of a known mass of water
    A calorie is defined as the amount of energy required to raise the temperature of 1g of water by 1°C, therefore: ENERGY (CALORIES) = MASS OF WATER (G) X TEMPERATURE CHANGE ( ° C) Expensive, difficult to operate & not a very suitable method for most people DISADVANTAGES Extremely accurate ADVANTAGES
  • Indirect Calorimetry
    • Since oxygen is usually required to release energy during respiration, it can be assumed that there is a relationship between oxygen consumption and energy expenditure
    • In fact about 4.8 kcal (20 kJ) of energy are released for every litre of oxygen used by an individual
    • Therefore an individual's energy expenditure can be INDIRECTLY ESTIMATED if the volume of oxygen taken in over a given period of time is known
    • In order to measure an individual's oxygen consumption we need to know the volume of air they have breathed in (inspired air), which is equal to the volume of air breathed out (expired air), and the proportion of oxygen in the air breathed in and out
  • Indirect Calorimetry
    • The volume of air is measured using a SPIROMETER , a large bag which collects the air breathed out over a given time period
    • The composition of oxygen in the inspired and expired air is measured
    • The percentage of oxygen absorbed by the individual is equal to the percentage of oxygen in the inspired air (usually 20%) minus the percentage of oxygen in the expired air
    Not as accurate as Direct Calorimetry DISADVANTAGES Much cheaper & easier to carry out ADVANTAGES
  • Heart Rate Recording
    • This method is related to Indirect calorimetry
    • There is a LINEAR RELATIONSHIP between heart rate and oxygen consumption
    • As the heart rate INCREASES the rate of oxygen consumption INCREASES
    • This relationship can be shown by calculating and graphing the oxygen consumption (l/min) and heart rate (beats/min) of an individual during different activities
    The relationship between heart rate and oxygen consumption for an individual
  • Heart Rate Recording
    • Once the graph of the relationship has been drawn, an individual can carry out a particular activity and use a heart rate monitor to record their heart rate during a given period of time
    • If they find their average heart rate in beats/min, they can read their oxygen consumption (l/min) from the graph
    • The total oxygen consumption for the duration of the activity can then be calculated
    • As we know that 4.8 kcal of energy are produced from every litre of oxygen used, therefore the energy expenditure can be estimated
    Not as accurate as Direct Calorimetry DISADVANTAGES Fairly accurate [ IF O 2 CONSUMPTION & HR MONITORING ACCURATE! ] and easy way ADVANTAGES