Energy

• Energy


  Capacity to do work
• Body processes


  • Require energy
• Plants


  • Synthesize energy from the sun through photosynthesis
  • Convert energy into macromolecules
• Humans


  • Gain energy from food intake through oxidation processes
• Kilocalorie (kcal)


  • Amount of heat required to raise the temperature of water by 1 Celsius at normal atmospheric pressure
  • Measurement used in Food Science and Nutrition
  • 1 kcal = 1 Calorie (Cal) = 1000 small/ gram calories (c)

  
• Joule (J)


  • Unit of measure of energy in the metric system
  • 1 small/gram calorie = 4.184 J
• Kilojoule (kJ)

  • Energy required to push against a force of 1 N for a distance of 1 meter
  • 1000 J = 1 kJ
  • 1 kcal = 4.184 kJ
• Calorimetry


  Measurement of the amount of energy or heat produced from food as heat energy expended by the body
• Direct calorimetry


  • Monitors the heat produced in a chamber

  
• Indirect calorimetry


  • Monitors oxygen consumption and carbon dioxide consumption over a period of time

  
• Direct calorimetry


  • Bomb calorimeter
  • Respiration Chamber
• Indirect calorimetry


  • Respiratory Quotient (RQ)
  • Closed Circuit
  • Open Circuit
  • Benedict Roth Respiration Apparatus
  • Kofranyi- Michaelis Respirometer
• Heart rate monitoring


  • Correlation between heart rate and oxygen consumption
  • Increased oxygen consumption requires increased blood flow thus increased heart rate
• Doubly-labeled water technique


  • Measures hydrogen atoms of the body water through losses and oxygen atoms as carbon dioxide gas
  • Uses stable isotopes of water with deuterium oxide
• Energy Balance


  Relation of energy intake to energy expenditure
• Positive energy balance


  • Energy intake is higher that expenditure
  • Induces anabolism
  • Child growth, pregnancy, weight gain
• Negative energy balance


  • Energy intake is lower than expenditure
  • Induces catabolism
  • Growth retardation and failure, weight loss
• Metabolizable fuel value (MFV)


  Maximum amount of energy that can be derived from food but does not consider complete utilization
• Physiological fuel value (PFV)


  Considers average digestibility
• Nutrient/ Food Component


  • Carbohydrates (4 kcals/gram, 98% digestibility)
  • Proteins (4 kcals/gram, 95% digestibility)
  • Fats (9 kcals/gram, 92% digestibility)
  • Alcohol (7 kcals/gram, varied digestibility)
• Carbohydrates


  • Delivered to the cells in the form of glucose
  • Fructose and galactose are converted to glucose in the liver
  • Oxidized via Krebs cycle
  • Some glucose are converted to other necessary carbohydrates (ribose, fructose) and as skeletons for the synthesis of nonessential Aas
  • Excess are converted to glycogen or FAs as TGs
• Fats


  • TGs are hydrolyzed to FAs and glycerol by lipoprotein lipase
  • Glycerol can be oxidized and metabolized as glucose
  • FFAs are released from adipose cells when needed for energy
  • FAs are metabolized in the liver by betaoxidation forming acetic acid and shorter chains of FAs
  • Final product is acetyl CoA with oxaloacetic acid and oxidized via Krebs cycle
  • Carnitine is essential for the oxidation of LCFAs
• Proteins


  • AAs are first deaminated and a keto acid is formed (Liver)
  • Carbon skeletons are converted into intermediate products and are then carried to peripheral tissues to enter the Krebs cycle via glucose (glucogenic AAs) or fat pathway (ketogenic AAs)
  • Amphibolic AAs are both glucogenic and ketogenic
  • Only Lys and Leu are exclusively ketogenic
• Hypothalamus


  • Responsible for feeding and satiety
• Neuropeptide Y


  • Stimulates appetite, diminishes energy expenditure and increases fat storage
• Leptin


  • Hormone encoded by the ob gene in adipose tissues that diminishes appetite and increases energy expenditure
• Hunger


  Feeling that motivates to eat, a painful sensation caused by lack of food that initiates food-seeking behavior
• Appetite


  Physiologic desire to eat, an integrated sensory response that initiates or delays eating
• Satiety


  Suppresses hunger and determines the time between meals, stops one from eating
• Satiation


  Maintains the signal not to start eating again, determines amount of food to be consumed in a meal
• Basal Metabolism


  • Basic essential metabolic processes required by the body at rest
  • Minimum amount of energy required for vital processes such as respiration, circulation and maintenance of body temperature and muscle tonus
  • Comprises approximately 2/3 of the daily energy expenditure
• Basal Metabolic Rate (BMR)


  Measured in kcal/kg/hr
• Resting Metabolism


  • Similar to basal metabolism but is measured under actual conditions and includes the thermic effect of food
  • Measured as Resting Metabolic Rate (RMR)
• Energy Expenditure of Organs


  • Liver (29%)
  • Brain (19%)
  • Heart (10%)
  • Kidney (7%)
  • Skeletal muscles (at rest) (18%)
  • Various (17%)
• Body composition-related conditions affecting BMR


  • Higher surface area, higher BMR
  • Higher muscle to fat ratio, higher BMR
  • Males have an average of 15% body fat; females have around 25 to 27% body fat
  • Pregnancy increases BMR by 20% during the 2nd and 3rd trimester
• Age affecting BMR


  • Gradually decreases after 2 years of age with a short-term rise during puberty
• Hormones affecting BMR


  • Thyroxine (decreased secretion can decrease BMR up to 30%, increased secretion can increase BMR up to 50 to 75%)
  • Adrenalin (Epinephrine) (short term increase)
• Sleep affecting BMR


  • Slight reduction
• Nutritional status affecting BMR


  • Prolonged calorie undernutrition can decrease BMR from 20 to 30%
  • Habitual high energy intake (luxus consumption) can increase BMR
• Temperature affecting BMR


  • A rise in 1 degree Farenheit in body temperature can increase BMR by 7%
  • 1 degree Celsius increase can increase BMR by 13%
  • Decrease in environmental temperature increases heat production for thermoregulation
  • Increase in environmental temperature also has the same effect