Spotlight on Metabolism and Energy Balance

Energy: Fuel for Work Energy source Chemical energy in carbohydrates, fat, and protein Transferring food energy to cellular energy Stage 1: digestion, absorption, and transport Stage 2: breakdown of molecules Stage 3: transfer of energy to a form cells can use 2

What Is Metabolism? Catabolism Reactions that break down compounds into small units Anabolism Reactions that build complex molecules from smaller ones 4

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What Is Metabolism? Cell is the metabolic processing center Nucleus Cytoplasm: cytosol + organelles Mitochondria are the source of many energy pathways 6

What Is Metabolism? Who are the key energy players? ATP is the body’s energy currency ATP = adenosine triphosphate Form of energy cell use NAD and FAD: transport shuttles Accept high-energy electrons for use in ATP production 8

Breakdown and Release of Energy Pathways initiate breakdown of macronutrients Anaerobic Breakdown glucose Do not require oxygen Aerobic Breakdown glucose, fat, and protein Require oxygen

Breakdown and Release of Energy Extracting energy from carbohydrate Glycolysis Pathway splits glucose into two pyruvates Transfers electrons to NAD Produces some ATP 12

Breakdown and Release of Energy Extracting energy from carbohydrate Pyruvate to acetyl CoA Releases CO2 Transfers electrons to NAD 13

Breakdown and Release of Energy Extracting energy from carbohydrate Citric acid cycle Releases CO2 Produces GTP (like ATP) Transfers electrons to NAD and FAD 15

Breakdown and Release of Energy Extracting energy from carbohydrate Electron transport chain Accepts electrons from NAD and FAD Produces large amounts of ATP Produces water End products of glucose catabolism ATP, H2O, and CO2 17

Breakdown and Release of Energy Extracting energy from fat Split triglycerides into glycerol and fatty acids Takes place in mitochondria Beta-oxidation Breaks apart fatty acids into acetyl CoA Transfers electrons to NAD and FAD 19

Breakdown and Release of Energy Extracting energy from fat Completing fatty acid breakdown Acetyl CoA from beta-oxidation enters cycle Citric acid cycle and electron transport chain Fat burns in a flame of carbohydrate End products of fat breakdown ATP, H2O, and CO2 21

Breakdown and Release of Energy Extracting energy from protein Split protein into amino acids Split off amino group Converted to urea for excretion Carbon skeleton enters breakdown pathways End products ATP, H2O, CO2, urea 22

Biosynthesis and Storage Making carbohydrate (glucose) Gluconeogenesis Uses pyruvate, lactate, glycerol, and certain amino acids Storing carbohydrate (glucose  glycogen) Liver and muscle make glycogen from glucose Making fat (fatty acids) Lipogenesis Uses acetyl CoA from fat, amino acids, and glucose Storing fat (triglyceride) Stored in adipose tissue 25

Biosynthesis and Storage Making ketone bodies (ketogenesis) Made from acetyl CoA When inadequate glucose in cells Making protein (amino acids) Amino acid pool supplied from Diet, protein breakdown, and cell synthesis Biosynthesis Different pathways used to build amino acids from carbon skeletons 27

Special States Feasting Excess energy intake from carbohydrate, fat, protein Promotes storage Fat  adipose tissue Amino acids  protein synthesis Carbohydrate  adipose tissue 29

Special States Fasting Inadequate energy intake Promotes breakdown Prolonged fasting Protects body protein as long as possible 30

Special States Fasting Survival priorities and potential energy sources Preserve glucose-dependent tissue RBC, brain cells, central nervous system Maintain muscle mass

Special States Fasting The prolonged fast: In the beginning Blood glucose drops, liver breaks down glycogen to glucose Gluconeogenesis Fat and protein are primary fuel

Special States Fasting The early weeks Several energy-conservation strategies Several weeks of fasting Rely on stored body fat The end is near Muscle atrophy and emaciation Sacrificed muscle tissue in attempt to preserve brain tissue

Energy Balance Energy intake vs. energy output Energy equilibrium Intake = output Maintain weight 34

Energy Balance Positive energy balance Intake > output Gain weight Negative energy balance Intake < output Lose weight 35

Energy In Regulation of intake Internal cues Hunger Prompts eating Satiation Signals to stop eating Satiety Tells when you are ready to eat again 36

Energy In Regulation of intake External cues Appetite Psychological desire to eat Influenced by the eating environment 38

Energy In Control by committee What stimulates our cues? Internal, physiological response Eating environment 39

Energy In Internal factors Gastrointestinal sensations Sense of fullness Neurological and hormonal factors Neuropeptide Y Ghrelin Leptin 40

Energy In External factors Diet composition Energy density, balance of energy sources, and form Macronutrients Sensory properties Taste 41

Energy In External factors Portion size Super-size culture Environment and social factors Hypothalamus Emotional factors 42

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Energy Out: Fuel Uses Total energy expenditure Major components of energy expenditure Energy expenditure at rest (basal energy expenditure) Energy for basic body functions Affected by body size, composition, age, and gender 44

Energy Out: Fuel Uses Major components of energy expenditure Physical activity Highly variable Affected by body size, fitness level, type of activity Thermic effect of food (TEF) Energy to digest, absorb, metabolize food 45

Energy Out: Fuel Uses Estimating total energy expenditure Resting energy expenditure (REE) 1.0 kcal/kg/hr for males 0.9 kcal/kg/hr for females Physical activity Add a % of REE (see Table 8.2) Thermic effect of food 6% to 10% of (REE + physical activity) 47

Estimating Energy Expenditure Estimated Energy Requirement (EER) Equations for males and females Factors for age, weight, height, and physical activity Predicts total energy expenditure (TEE) 48

Body Composition Body composition Fat and lean muscle mass Assessing body weight Body mass index (BMI) Weight (kg) × height2 (m) BMI ≤ 18.5 kg/m2 = underweight BMI 18.5 to ≥ 25 kg/m2 = normal weight BMI 25 to ≤ 30kg/m2 = overweight BMI ≥ 30 kg/m2 = obese 49

Body Composition Assessing body fatness DXA Underwater weighing BodPod Skinfold measurements Bioelectrical impedance 50

Body Composition Body fat distribution Gynoid obesity (“pear”) Excess fat in hips and thighs Android obesity (“apple”) Excess fat around abdomen Waist circumference 51