Energetics
An RQ of .7 means that a. carbohydrate is being utilized for fuel b. protein is being utilized for fuel c. fat is being utilized for fuel d. the person consumed a mixed meal
fat is being utilized for fuel
Respiratory Quotient
RQ= the amount of carbon dioxide exhaled divided by the amount of oxygen inhaled
Total Energy Expenditure All cellular-energy-requiring operations fall within three groups:
1. Membrane transport 2. Synthesis of molecules 3. Mechanical work
The thermic effect of food peaks about one hour after ingestion of a meal and wanes after _____ hours. a. 7 b. 5-6 c. 2 d. 3-5
3-5
Components of Energy Expenditure •Thermoregulation
Alterations in metabolism that occur as the body maintains its internal temperature in response to environmental temperature and radiant energy.
Which of the following organs has the greatest contribution to total resting energy expenditure? A. Liver B. Heart C. Skeletal Muscle D. Brain
Skeletal Muscle
What are the components of energy expenditure?
Thermic Effect of Food Energy Expenditure from Physical activity Adaptive Thermogenesis Thermoregulation
Total Energy Expenditure Most energy released by the body becomes
heat energy
Ghrelin increases before meals and decreases after meals and it a. decreases with weight loss b. tends to increase food intake c. promotes satiety d. circulates in proportion to fat volume
tends to increase food intake
Total Energy Expenditure metabolic rate
the measurement of energy liberated over a specific time period.
Regulation of Body Weight & Composition •Hormonal and chemical influences •Leptin
•Amount synthesized and released by adipocytes relative to fat stores •Reduces food intake •Increases energy expenditure •Leptin resistance •obesity •Decrease with weight loss
Regulation of Body Weight & Composition •Hormonal and chemical influences •Insulin
•Circulating levels typically proportionate to fat volume •Crosses blood brain barrier •May reduce feeding by inhibiting expression of neuropeptide Y, enhancing CCK, and inhibiting neuronal norepinephrine. •Reducing appetite by be leptin mediated
Regulation of Body Weight & Composition •Hormonal and chemical influences •Arcuate nucleus in hypothalamus releases Neuropeptide Y
•Energy deficit •Stimulates food intake (esp carbohydrates) •Seems to reduce energy expenditure •Seems to promote fat storage
Components of Energy Expenditure Resting energy expenditure •RMR and REE
•Energy expended •thermoneutral environment •motionless •Post absorptive state
Components of Energy Expenditure •Basal Metabolic Rate (BMR)
•Expenditure for respiration, heartbeat, renal function, blood circulation •Energy expended by internal processes •during a period of rest •in a climate-controlled room- thermoneutral environment •at least 10-12 hrs after last meal
Assessing Energy Expenditure Derived formulas
•Harris-Benedict •Men: BMR = 66.5 + (13.7 x W) + (5.0 x H) - (6.8 x A) •Women: BMR = 655.1 + (9.56 x W) + (1.85 x H) - (4.7 x A) •Mifflin-St. Jeor •Men: REE = (10 x W) + (6.25 x H) - (5 x A) + 5 •Women: REE = (10 x W) + 6.25 x H) - (5 x A) - 161
Metabolically Active Tissues
•Heart •Kidneys •Lungs •Brain •Liver
Regulation of Body Weight & Composition •Hormonal and chemical influences Galanin
•Increases feeding of carbohydrates & fats •Decreases energy expenditure by inhibiting sympathetic nervous system activity
Indirect Calorimetry
•Indirect calorimetry estimates energy expenditure and the energy substrates being used during the time of measurement. •ATP is generated from the combustion of energy molecules (combustion requires oxygen and produces carbon dioxide). •Energy expenditure is estimated from the gas exchanges process. •Indirect calorimetry is assessed with a metabolic cart.
Examples of Heat-Conserving and Heat-Producing Operations
•Less blood circulates to the periphery •Decreased production of sweat •Piloerection (hair standing on end) •Shivering •Nonshivering thermogenesis •Chemical thermogenesis •Increased thyroid hormone and increased thyrotropin-releasing hormone, which increases thyroid-stimulating hormone, increasing the metabolic rate
Assessing Energy Expenditure •Indirect calorimetry
•Measures consumption of O2 & expiration of CO2 •The respiratory quotient & substrate oxidation •The respiratory quotient & energy expenditure
Assessing Energy Expenditure •Direct calorimetry
•Measures dissipation of heat from the body
Regulation of Body Weight & Composition •Hormonal and chemical influences •Ghrelin
•Produced by stomach and pancreas •Increase before meals •Decrease after meals •Orexigenic •Tends to increase food intake •Increase fat mass by effect on hypothalamus
Components of Energy Expenditure •Thermic effect of food
•Protein increases expenditure 20%-30% •CHO: 5%-10% •Fat: 0%-5% •TEF peaks about 1 hour after ingestion of a meal and wanes after 3-5 hours.
Rq of 1 Rq of 0.7 Rq of 0.818 Rq for a mixed meal? What Rq suggests lipogenesis
•RQ = 6CO2/6O2 = 1.0 for carbohydrate •RQ = 0.7 for fat •RQ = 0.818 for protein •RQ ~ 0.85 for a mixed meal •RQ = 1 suggests lipogenesis
Heat Loss
•Radiation (60% of heat loss) •Convection (15% of heat loss) •Evaporation (22% of heat loss) •Conduction (2-3% of heat loss) •When environmental temperature increases, heat production decreases. •When environmental temperature decreases, heat-conserving and heat-producing operations increase.
Regulation of Body Weight & Composition •Hormonal and chemical influences •CCK
•Secreted by mucosal cells of proximal SI in response to food components. •Suppresses appetite promotes satiety •By signals of vagal afferents to brain and eventually to hypothalamus to decrease food intake.
Assessing Energy Expenditure •Doubly labeled water
•Stable isotopes of water given as H218O & 2H2O •Disappearance of H218O & 2H2O measured in blood & urine for ~3 weeks •Best method for free living subjects.
Metabolism facts
•To safely increase RMR, increase the skeletal muscle-to-fat ratio. •Men have a greater skeletal muscle:adipose tissue ratio than women. •RMR is higher in infants and decreases with age.
