Energy Release From Macronutrients

The Concept of Energy Balance

What Is Energy Balance and Why Is It Important? Energy balance is achieved when the kilocalories consumed equal the kilocalories expended

Foods and their conversion to energy Food is consumed =chemical energy  converted into mechanical energy (muscular contractions & movement) Carbohydrates, fats and protein are the only sources of food energy and fuel.

Energy (ATP) is stored in small amounts, therefore the rest is stored as: Glucose = Glycogen (muscle & liver) Fatty Acids = Body fat Amino Acids = Growth, repair or excreted as waste

Carbohydrates Sugars and starches = body’s preferred source of fuel  esp. during exercise. Carbohydrates = primary energy source during anaerobic exercise of high intensity and short duration. Carbohydrates are broken down and stored as glucose in the blood and glycogen in the muscles and liver. Excess carbs are stored around the body as adipose tissue (fat tissue)

7 CARBOHYDRATE SOURCES Carbohydrates come in two sources: – Simple sugar glucose – Storage form of glucose  glycogen Glycogen is stored in – Muscles – Liver – Blood (smallest % in blood) Liver = only tissue that can release stored glycogen in the form of glucose Liver = maintain blood sugar levels by releasing glucose through gluconeogenesis & glycogenolysis

Carbohydrates All carbohydrate converted to glucose – Primary ATP substrate for muscles, brain Glycogen converted back to glucose when needed to make more ATP Glycogen stores limited (2,500 kcal) = must rely on dietary carbohydrate to replenish

Energy from Carbohydrates Glucose is absorbed from the intestines into the blood and broken down by glycolysis Excess glucose intake stimulates storage as glycogen and fatty acids

Energy Release From Carbs Carbs primary function to supply energy for cellular work Carbs = only macronutrient whose stored energy generates ATP anaerobically  NB for maximal exercise that requires rapid energy release  intramuscular glycogen stores supplies most of the energy for ATP resynthesis

Energy Release From Carbs During light & moderate aerobic exercise  carbs supply 1 / 3 of body’s energy requirements Breakdown of carbs for energy supply occurs more rapidly than breakdown of fats. = depletes glycogen reserves significantly = reduces exercise power output Prolonged exercise (marathon runners) = muscle & liver glycogen depletion

Energy from Carbs and Physical Activity Carbs provide QUICK ENERGY. They supply energy for both AEROBIC & ANAEROBIC physical activity Used for physical activity of a comparatively SHORT length of time and HIGH INTENSITY

Fats Fats = butter, oils, nuts. Fat = body’s preferred source of fuel at rest. More oxygen is required by the body to use fat as a fuel than to use carbs to produce ATP.

14 FAT SOURCES Fat for fuel is in the form of free fatty acids – Two sources of these fats are: Peripheral fat stores – Rolls of fat on the stomach, glutes… Intramuscular fat – Triglyceride stored in the actual muscle

Most Body Fat Is Stored in Adipose Tissue Two types of fat make up total body fat: Essential fat Found in bone marrow, heart, lungs, liver, spleen, kidneys, intestines, muscles, and central nervous system Women have 4x more essential fat than men Stored fat Found in adipose tissue Subcutaneous fat – located under the skin Visceral fat – stored around the organs in the abdominal area

Fats Fats have the capacity to produce much more ATP than carbs BUT: the conversion rate is much less efficient  require much more oxygen to produce the same amount of ATP. Fatty acids are stored in the blood, triglycerides in the muscles Excess fats are stored as adipose tissue around the body

Energy from Fats The body stores most fats as triglycerides When blood glucose falls, enzymes break triglycerides into glycerol and fatty acids – Glycerol enters the energy cycles to be converted to glucose Fatty acids yield more energy (ATP) than carbs

Fat Efficient substrate, efficient storage – +70,000 kcal stored in body Energy substrate for prolonged, less intense exercise – High ATP yield but slow ATP production – Must be broken down into free fatty acids (FFAs) and glycerol – Only FFAs are used to make ATP

Fat release for energy and physical activity Fats provide SLOW ENERGY The energy release from fats is too slow to be used when used when working hard Used for walking and low-impact exercise Used for exercise of a longer duration, and MODERATE INTENSITY Physical activity of LONG DURATION and HIGHER INTENSITY is fuelled more from fat stores in the body because the glycogen store becomes depleted

Protein Protein includes meat, fish, poultry, dairy, eggs & lentils. Protein is used for growth & repair of the body & as fuel source in extreme situations. Body only uses protein as energy source when glycogen & fat sources have already been depleted.  ie. marathon or starvation

Energy from Proteins Proteins enter the bloodstream as amino acids Amino acids can be used for energy by removing the amino group (as ammonia)

Energy release from Protein Energy yield not easy to determine – Nitrogen presence unique – Nitrogen excretion requires ATP expenditure – Generally minimal, estimates therefore ignore protein metabolism

23 Fuel Utilization is Determined by Energy Output or Intensity Level First thing in the morning before you eat breakfast = energy demands are very low  can be met mainly by fat derived from blood free fatty acids Free fatty acids are released at a low rate by peripheral fat stores This allows the muscles to preserve both intramuscular fat and glycogen stores

24 Exercise Intensity and Duration For all energy substrates, carbs and fats, ultimately ATP is generated in the muscle cell as the high energy substrate for moving muscle. Carbs can also be broken down in the absence of oxygen for limited energy production

25 Fuel Utilization - Intensity Low intensity – Walking: energy output can be generated entirely by peripheral fat stores releasing free fatty acids – Stimulus to increase FFA release to maintain enough blood concentrations of FFA for uptake by the working muscles

26 Moderate Intensity Exceeds the capacity of peripheral fat stores to supply enough free fatty acids to meet energy output rates= – Intramuscular triglycerides are broken down to provide more fat sources – Peripheral fat uptake does not stop  it plateaus – + another source is provided to makeup the needed energy…(glucose/glycogen)

27 Medium/ Moderate Intensity A medium intensity pace can be maintained until either your intramuscular fat stores are depleted or you run out of glycogen – When the glycogen is depleted then protein is broken down for energy

28 High Intensity High Intensity exercise goes above the limits of energy production rates that fats can supply and requires additional energy derived from glucose  glucose requires less oxygen per unit of energy At lower intensities, the energy production rate is low enough that oxygen is plentiful enough for fat burning

29 Very High Intensity At very high intensities the aerobic system reaches its limitations for energy generation (fat or glucose) The anaerobic system takes over Only a little of the potential energy of glucose is released but is done so in a very rapid manner to meet short duration and very high energy production rates

30 The Benefits of Exercise At Any Intensity Low intensity exercise is not the is not the best form for weight loss Intramuscular stores (fat or glycogen) are depleted – During the recovery phase (post exercise) fats and carbs from the diet will go to restoring those levels High intensity exercise can lead to fat loss  depletion of glycogen & glycogen stores must be replenished with dietary carbs that would otherwise be burned for energy While the storage process occurs = the body will burn extra fat to supply current energy needs