Energy Sources

• The energy content of food can be estimated by burning a sample of known mass and measuring the energy released via calorimetry
• The amount of energy required to raise 1 g of water by 1ºC is 4.18 J – this is the specific heat capacity of water
• One calorie is equal to 4.18 kiloJoules
• The equation for calculating the energy content of a food source via calorimetry is as follows:

  Energy (joules) = Mass of water (g) × 4.2 (J/gºC) × Temperature increase (ºC)
• The biggest source of error in calorimetry is usually caused by the unwanted loss of heat to the surrounding environment
• The three types of nutrients that are commonly used as energy sources are carbohydrates, lipids (fats) and proteins
• Carbohydrates are preferentially used as an energy source because they are easier to digest and transport
• Lipids can store more energy per gram but are harder to digest and transport (hence are used for long-term storage)
• Protein metabolism produces nitrogenous waste products which must be removed from cells