energy intake and expenditure

• Gross efficiency


  Percentage of work accomplished divided by energy expended
• Net efficiency


  Percentage of work accomplished divided by energy expended minus resting energy expenditure
• Work efficiency


  Percentage of work accomplished divided by energy expended minus energy expenditure in unloaded
• Delta efficiency


  Percentage of change in work accomplished divided by change in energy expenditure
• The oxidation path of a human and a bomb calorimeter differ
• The quantity of energy liberated from the complete breakdown of these foods remain the same
• Energy content per gram

  • Lipid - 9.45 kcal
  • CHO - 4.3 kcal
  • Protein - 5.65 kcal
  • Alcohol - 7 kcal
• Energy content and digestibility

  • CHO - 4 kcal/g, 97% digestible
  • Fat - 9 kcal/g, 95% digestible
  • Protein - 4 kcal/g, 92% digestible
  • Alcohol - 7 kcal/g, 100% digestible
• Energy in


  • Food
  • CHO
  • Lipids
  • Proteins
  • Alcohol
• Energy out


  • Basal metabolism (60-75%)
  • Thermogenesis (10%)
  • Physical activity (15-30%)
• Total Daily Energy Intake (TDEI) = Total Daily Energy Expenditure (TDEE) when body weight remains stable
• TDEI<TDEE results in negative energy balance, where the body uses stored energy to make up the difference
• Components of energy expenditure

  • TDEE - total daily energy expenditure
  • ADMR - average daily metabolic rate
  • BMR - basal metabolic rate
  • RMR - resting metabolic rate
  • TEF - thermic effect of food
  • DIT - diet induced thermogenesis
  • TEE - thermic effect of exercise
  • EEA - energy expenditure for physical activity
• Biggest change in energy expenditure is during marathon running at 800-1200 kcal/h
• Thermic effect of food includes both obligatory (digestion, absorption, assimilation) and facultative (metabolic load) components
• Direct calorimetry chamber


  • Small insulated chamber with adequate ventilation
  • Water flows through coils to absorb heat and measure metabolic rate
  • Air is recirculated with CO2 and H2O filtered out
  • Requires specially trained individuals
  • Suit can be an option
• Respiration chamber


  • No heat exchange
  • Measures oxygen in and carbon dioxide out
  • Can measure over several hours to days
  • Food intake can be accurately measured
  • Urine and faeces can be collected to measure energy and nitrogen balance
  • Highly trained personnel required
  • Expensive and potentially boring
• Indirect calorimetry


  • Douglas Bag Technique - one sample of expired air in allotted time, Haldane transformation
  • Breath by Breath Systems - immediate analysis, continuous measurement
• For every litre of oxygen used, 5 kcal are available from carbohydrate and 4.7 kcal from fat
• Consumption of 1L O2 is equivalent to 5 kcal of energy expenditure
• Resting energy expenditure of 0.25 L O2 per minute for 1 hour is 75 kcal
• Indirect calorimetry methods


  • Heart rate
  • Accelerometers
  • Questionnaires
• Doubly labelled water


  • 2H2 18O
  • Hydrogen is excreted independent of metabolic rate
  • Oxygen excreted as carbon dioxide and water
  • CO2 production = difference in H and O isotopes excretion
  • More O = inc EE
  • Free living
  • Expensive
• Energy cost of activities

  • Very light activities - 3-5 kcal/min, 12-20 kJ/min
  • Light activities - 5-7 kcal/min, 20-28 kJ/min
  • Moderate activities - 7-9 kcal/min, 28-36 kJ/min
  • Strenuous activities - 9-13 kcal/min, 36-52 kJ/min
  • Very strenuous activities - >13 kcal/min, >52 kJ/min
• The energy cost of running can be roughly estimated as 1 kcal per kg body mass per km
• The energy intake and expenditure during the Tour de France can reach 9000-11000 kcal per day
• Some athletes have very low energy intake despite 3-4 hours of training per day, which reduces their thermic effect of food and resting metabolic rate
• Energy intake as low as 1000-1500 kcal per day with lots of exercise can lead to loss of muscle mass, anaemia, secondary amenorrhea, decreased body mass, and low bone mineral density
• Methods for assessing energy intake

  • 24 hour recall
  • 3 day food diary
  • 7 day food diary
  • Food frequency questionnaire
  • Diet history
• 24 hour recall


  Trained interviewer asks what the person has eaten and drunk in the last 24 hours, relies on memory
• Food diaries


  Record everything eaten over 3 or 7 days, can be weighed or not
• Food frequency questionnaires


  Not used for accurately measuring exact energy intake, used to assess wider population intake of certain foods
• Diet history


  General assessment of what the person has eaten in the past
• Most people will underreport their energy intake by around 20%, making results in certain populations unreliable