Role of Metabolism in Nutrition

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Role of Metabolism in
Nutrition Definition the sum of all
biochemical changes that take place in a living
organism. Group these reactions into two types
anabolic catabolic
Reactions require energy release
energy Produce more complex more
simple compounds compounds Modus Operandi
Occurs in small steps, each of which is
controlled by specific
enzymes.
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Examples of each type of
metabolism Anabolic Pathways Catabolic
Pathways Protein Biosynthesis Glycolysis Glyco
genesis TCA (Krebs cycle) Gluconeogenesis ß
-oxidation Fatty Acid Synthesis Respiratory
Chain Other useful generalizations Some of
the steps in the anabolic path (going uphill)
may not be identical to the catabolic path--but
some are shared.
ATP Generated Provides Energy
FOR
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Metabolism Who Needs It? Average
American consumes 1450 lbs of food each
year. Assuming that 98.2 of this energy is
metabolizable, 1424 lbs is used to supply
our needs. Supplies roughly 1 x 106 kcals/
year
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How do we employ energy? MECHANICAL-
muscle contraction ELECTRICAL- maintaining
ionic gradients (e.g., Na-K ATPase 70
of ATP used by kidney brain used to
maintain gradient) CHEMICAL-
biotransformation of molecules (e.g.,
synthesis degradation, metabolism)
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International Unit of Energy Joule
energy used when 1 Kg is moved 1 meter
by a force of 1 Newton kJ 103
J MJ 106 J 1 kcal 4.184
kJ Protein 17 kJ or 4
kcal/g CHO 17 kJ or 4
kcal/g Fat 37 kJ or 9 kcal/g
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Average Energy
Needs European text 100 kJ/ day x BW in
kg or 24 kcal/day x BW
in kg American Biochem text 129-184 kJ/
kg or 31-44 kcal/kg
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Conversion Efficiency Food to Usable Energy
40 used to make high energy phosphate bonds
60 lost (?) as heat
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What are the components of energy
expenditure? Basal metabolic rate Definition D
eterminants Calculation
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Energy Expenditure Component 2 THERMIC EFFECT
OF FOOD Definition Determinants Contributio
n to Total Energy Expenditure
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Components of Energy Expenditure- 3 Physical
Activity Contribution to Total
Expenditure What about accounting for changes
in energy expenditure due to injury or trauma?
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Maintaining Body
Composition Fuel Utilization
in Maintenance and Injury Average Adult
Composition
(w/w) Water 55 Protein 19 Adipose
Tissue 19 CHO lt1 Inorganic matter 7
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Recommended Fuel
Sources (
of kcal) Source of kcals
DRVs Atwater Fat 30
33 Protein 10
15 CHO 60 52 W.O.
Atwater (1894), USDA Scientist credited with
deriving physiologic energy values of pro, CHO,
fat. PROGRESS!!!
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Fuel Sources During
Exercise Normal ADL LIGHT MODERATE
HEAVY
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OVERVIEW OF METABOLISM Too
Much, Too Little, Too Stressed Energy Economy in
Feasting Metabolic Adaptation to
Starvation WHO Guidelines for Treatment
of Severe Malnutrition Fuel Utilization in
Hypermetabolic States
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Reclaiming Energy From Stored Fuel Sources By
Choice Fasting By Necessity Starving
Exhaustion of labile CHO Exhaustion of stored
CHO Problem certain tissues require glucose
for energy Tapping into stored
protein Short-term effect and
contribution If this contribution continues
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Adaptation to Starvation/
Fasting Building glucose in the absence of
labile or stored CHO After deamination, the
carbon skeletons of some amino acids can be used
to make glucose or ketone bodies
(ketoacids). Gluconeogenesis the formation of
glucose from lactate, some amino acids, and
glycerol Long-term dependence on GNG to fuel
brain is not feasible. Switch to ketone
production within 10 d of fast --
provides majority of energy for brain. Protein
sacrificed for glucose production for parts of
brain requiring it.
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Benefits of Ketosis provides needed source
of energy suppresses appetite. Concomitant
Changes in Energy Expenditure Wasting results in
decreased energy expenditure
Heart mass Lung mass Skeletal
muscle
Hormonal response to fasting leads to energy
conservation
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Metabolic Adaptations to
Fasting/Starvation ADVANTAGES
DISADVANTAGES Advantages Disadvantages
Energy Expenditure Wasting of
muscle mass Body Temperature Decreased
immune Enhanced Survival
competence
See guidelines for the inpatient treatment
of severely malnourished children London
School of Hygiene and Tropical Medicine.
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Full thickness
Burns trauma sepsis
Who Are The Critically Ill?
GI Cardiac Renal Cancer
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Injury, Trauma, Surgery Neurohormonal
Activation of the Stress Response Glucocort
icoid Catecholamine Activation, Hi
GlucagonInsulin Ratio, Growth Hormone
Release Tachycardia, Tachypnea,
Hyperglycemia, Mobilization of Body Fat,
Massive Catabolism of Skeletal Muscle
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In Critical Illness, Timing of Assessment
is Extremely Important!
Why?????
Metabolism in critical injuries goes through at
least three distinct phases Ebb (1st 24 hrs
post-injury) Flow (Days 2-5) Anabolic (7-10 days)
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Nutrition Support in Stress
Immediate Needs to Sustain Life Restore blood
flow Maintain oxygen transport Prevent/treat
infections.
If malnourished, introduce nourishment cautiously,
if not--
Refeeding syndrome malabsorption,
cardiac insufficiency, respiratory distres
s, CHF, etc.
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Fluid and Electrolytes Many types
of stress can cause massive fluid
losses. Examples Severe burns lose
12-15 of BW is FIRST 24 hours!
Vomiting, diarrhea, wounds, bleeding, and
FEVER
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Energy Metabolism in Critical
Injuries Response to Injury Separable into Two
Phases Ebb Phase 1st 24 hours
post-injury Characterized by low cardiac flow,
tissue perfusion Priority of Metabolism in
Ebb resuscitation maintain tissue
perfusion Hormonal response catecholamines
increase availability of energy-yielding
substrates (glucose, aa, ffa)
But.substrate utilization in depressed.
No additional nutrition support needed
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Second Phase Flow or Hypermetabolic Phase 1.
Massive increase in catabolic hormone
release (e.g., glucagon, catecholamines,
etc.) 2. High cardiac output 3. Increased
insulin secretion 2to 1 insulin
resistance may exacerbate
hyperglycemia. 4. Energy sources? Glycogen
gone. 80 fat stores 20
endogenous protein Water/Na
retention urinary N losses
N Balance Possible? No way, baby.
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Late Flow Phase Anabolism now
possible Catecholamines decrease, energy needs
Decrease, N balance begins to approach
zero. Assessment of Energy Needs BEE X
Activity Factor X Injury Factor Warning!
May overestimate needs! Overfeeding may
precipitate Respiratory Failure.