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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 What Is Metabolism? • Catabolism – Reactions that break down compounds into small units • Anabolism – Reactions that build complex molecules from smaller ones What Is Metabolism? • Cell is the metabolic processing center – Nucleus – Cytoplasm: cytosol + organelles • Mitochondria are the source of many energy pathways 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 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 Breakdown and Release of Energy • Extracting energy from carbohydrate – Pyruvate to acetyl CoA • Releases CO2 • Transfers electrons to NAD Breakdown and Release of Energy • Extracting energy from carbohydrate – Citric acid cycle • Releases CO2 • Produces GTP (like ATP) • Transfers electrons to NAD and FAD 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 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 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 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 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 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 Special States • Feasting – Excess energy intake from carbohydrate, fat, protein • Promotes storage –Fat adipose tissue –Amino acids protein synthesis –Carbohydrate adipose tissue Special States • Fasting – Inadequate energy intake • Promotes breakdown – Prolonged fasting • Protects body protein as long as possible 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 Energy Balance • Positive energy balance – Intake > output – Gain weight • Negative energy balance – Intake < output – Lose weight Energy In • Regulation of intake – Internal cues • Hunger –Prompts eating • Satiation –Signals to stop eating • Satiety –Tells when you are ready to eat again Energy In • Regulation of intake – External cues • Appetite –Psychological desire to eat –Influenced by the eating environment Energy In • Control by committee – What stimulates our cues? • Internal, physiological response • Eating environment Energy In • Internal factors – Gastrointestinal sensations • Sense of fullness – Neurological and hormonal factors • Neuropeptide Y • Ghrelin • Leptin Energy In • External factors – Diet composition • Energy density, balance of energy sources, and form • Macronutrients – Sensory properties • Taste Energy In • External factors – Portion size • Super-size culture – Environment and social factors • Hypothalamus – Emotional factors • Hypothalamus 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 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 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) 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) 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 Body Composition • Assessing body fatness – DXA – Underwater weighing – BodPod – Skinfold measurements – Bioelectrical impedance Body Composition • Body fat distribution – Gynoid obesity (“pear”) • Excess fat in hips and thighs – Android obesity (“apple”) • Excess fat around abdomen – Waist circumference