Whole body metabolism Energy metabolism: the way the body stores and utilizes energy Driving concepts for energy metabolism • Intermittent food intake • Blood glucose level must be maintained at all time for activity of the brain Metabolic processes • Anabolism • Catabolism Energy Intake, Utilization and Storage Possible fates of small molecules from digestion: To be used for energy To be used to synthesize other molecules for function, growth and repair To be used to synthesize larger molecules for storage (e.g glycogen and triglycerides) Energy balance • Energy input = energy utilization + energy output • Energy input = work performed + heat released Metabolic Rate • Metabolic rate is the amount of energy expended per unit time • Basal metabolic rate (BMR) is the metabolic rate when both the metabolic rate and the work performed are minimal • BMR is estimated by measuring oxygen consumption • BMR is expressed as the rate of energy expenditure per unit of body weight • Average BMR in adults; 20-25 Kcal/ Kg/day Most of the BMR is due to the nervous system (40%) and skeletal muscles (20-30%) Negative and positive energy balance • Energy balance is maintained when the energy input equals the energy output • An imbalance occurs when energy input does not equal energy output -> a positive or negative energy balance • Positive energy balance: energy (nutrients) is taken in at a greater rate than what is expended as heat and work Weight gain occurs • Negative energy balance: energy intake is less than the rate at which the energy is expended Weight loss occurs Metabolic reactions of the absorptive state • Anabolic processes to synthesize macromolecules (glycogen, triglycerid, protein) • Body’s energy needs are supplied mainly by absorbed glucose • If the meal is reach in fats and protein, absorbed fatty acids and amino acids can also be catabolized for energy (oxidation of fatty acids –> acetyl CoA-> Krebs cycles; amino acids ->keto acids -> Kreb cycles) • Synthesized proteins are mainly for structural and functional roles, not for energy storage Energy reserves • The body has limited ability to store energy in the form of protein and glycogen but unlimited ability to store energy as fats • Triglyceride synthesis is common pathway for all excess absorbed nutrients • Fats: 30% (normal person); 80% in obese person • Triglycerides: Kcal/gr (70-80% of total body energy reserves- months); Carbohydrates: 4KCal/gr (1% -few hours); protein: 5-6 Kcal/gr (20-25%unavailable for use) Metabolic reactions of the postabsorptive state • • 2-3 hours after meal Catabolic process converting glycogen, proteins, fats to energy • Maintain plasma glucose levels • Glucose is mainly used for nervous tissue and supplied from from glycogen (short supply-few hours) and gluconeogenesis • Most tissues use other energy sourses (fatty acids) to conserve glucose for nervous tissue- Glucose sparing Insulin and Glucagon regulate absoptive and postabsortive metabolism