Role of Metabolism in Nutrition

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					         Lesson 2 :
Role of Metabolism in Nutrition
• Metabolism – process by which living
  systems acquire and use free energy to
  carry out vital processes
• Catabolism (degradation)
  – Nutrients and cell constituents are broken
    down for salvage and/or generation of energy
  – Exergonic oxidation
• Anabolism (biosynthesis)
  – Endergonic synthesis of biological molecules
    from simpler precursors
  – Coupled to exergonic processes through
    “high-energy” compounds
           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
Operandi: Occurs in small steps, each of which is controlled
          by specific enzymes.
 Relationship Between Catabolic and
         Anabolic Pathways

• Catabolic pathways
  – Complex metabolites are transformed into
    simpler products
  – Energy released is conserved by the synthesis
    of ATP or NADPH
• Anabolic pathways
  – Complex metabolites are made from simple
  – Energy-rich molecules are used to promote
    these reactions
           Examples of each type of metabolism:

Anabolic Pathways                           Catabolic Pathways

Protein Biosynthesis          ATP           Glycolysis
Glycogenesis                  Generated     TCA (Krebs cycle)
Gluconeogenesis               Provides      ß-oxidation
Fatty Acid Synthesis          Energy        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.
     Metabolism: Who Needs It?

Average American consumes ~ 1450 lbs ( 600kg) of food
      each year.

Assuming that 98.2% of this energy is
metabolizable, 1424 lbs ( 590kg) is used to supply our

Supplies roughly 1 x 106 kcals/ year
              Energy needs
 Measurement of Energy Intake

Diet Surveys
• Dietary and nutritional survey of British
  Adults (Gregory 1990)
• Average UK dietary energy intake
• Men 10.2 MJ (2400 kcal/d)
• Women 7.02MJ (1650 kcal/d)
    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)
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
                 Energy needs
Measurement of Energy Intake
Metabolic Energy Yields

  Fuel                 K J /g   K c a l/g
  Fat                  38       9
  A lc o h o l         29       7
  C a rb o h yd ra te s 1 7     4
  P ro te in           16       4
             Average Energy Needs:

European text:           100 kJ/ day x BW in kg
                         24 kcal/day x BW in kg

American Biochem text:     129-184 kJ/ kg
                            31-44 kcal/kg
Conversion Efficiency: Food to Usable Energy

                                    40% used to make
                                    high energy phosphate

                                    60% “lost” (?) as
 How to measure energy in food
• Direct Calorimetry
   – Direct measurement of heat produced
   – Bomb calorimeter

• Calculate
   – Calories/g: 4 (cho), 9 (fat) ,4 (prt) and 7 (alcohol)
   – based: lab analysis of food composition

• Calorie chart or nutrient database
               Energy needs
  Measurement of Energy Intake

Bomb Calorimeter
• Food is ignited electrically in the presence
  of oxygen
• Heat of combustion is measured from a rise
  in water temperature
Bomb Calorimeter measures heat
       produced when food is burned
Text view of bomb calorimeter
              Energy needs
  Measurement of Energy Intake
Bomb Calorimeter
• Heat of combustion represents the gross
  energy of the food
• Energy lost during digestion and absorption
• Affected by illness
                              Energy needs
   Measurement of Energy Intake
      % Energy from carbohydrates, protein and fat

       Food               T o ta l e n e rg y      % E n e rg y       % E n e rg y        %
                           c o n te n t o f           fro m              fro m        E n e rg y
                          s e rv in g (k J )    c a rb o h yd ra te    p ro te in    fro m fa t

   C h o c o la te            1195                     43                  6            51

       Peas                    230                     47                 35            18

C h ic k e n B re a s t       1138                      0                 75            24

 P o ta to b o ile d           535                     89                 10             1
Energy Balance: Input vs Output
           Energy Balance
• Energy In = Energy Out
  – Weight Maintenance
• Energy In > Energy Out
  – Weight Gain
• Energy In < Energy Out
  – Weight Loss
              Energy Balance
• Sources of fuel for energy
   – Input from diet: carbs, fat, prot, alcohol
   – Stored energy: glycogen, fat, muscle
• Energy outgo from:
   – Basal metabolism
   – Physical activity
   – “Dietary thermogenesis”
                Energy In
• Food and Beverages
  – Food composition tables
  – Bomb Calorimetry
• Complex social, environmental,
  physiological control
           Energy Out
• Energy of food = Body Energy = ATP
  – Overall efficiency 25%, 75% released heat
• Energy out:
• 3 main components:
  – Basal Metabolic Rate
  – Thermic Effect Food
  – Physical activity
BMR > Activity > Dietary Thermogenesis
               Energy needs
  Measurement of Energy Output

Energy Output
Energy of food        ATP + Heat Loss
• 50% efficiency

     ATP              “Work “+ Heat Loss
• 50% efficiency

     “Work “          Heat
              Energy needs
  Measurement of Energy Output

Energy Output

  Measurement            Measurement of
    of heat               energy used

• Two methods
• direct calorimetry
• indirect calorimetry
          Energy needs
Measurement of Energy Output
direct calorimetry
• Measurement of heat loss
             Energy needs
  Measurement of Energy Output

Indirect calorimetry
• Utilisation of oxygen
• Oxygen consumption is proportional to
  ATP synthesis
• Use oxygen consumption to determine heat
                 Energy needs
 Measurement of Energy Output
 Indirect calorimetry
 • Glucose oxidation
 C6H12O6 + 6O2      6H2O + 6CO 2 + 15.5 kJ/g of energy

 • Starch oxidation

(C6H12O5)n + 6nO2     5nH2O + 6nCO 2 + 17 kJ/g of energy
                    Energy needs
   Measurement of Energy Output

Indirect calorimetry
• Fat oxidation
(e.g. glyceryl butro-oleostearate (main fat in butter)

     C3H5O3.C4H7O.C18H33O. C18H35O        + 60O2

          43CO2 + 40H2O         +    39 kJ/g of energy
            Energy needs
Measurement of Energy Output
Indirect calorimetry
• Respiratory quotient (RQ)
• CO 2 Produced / O 2 Consumed
• RQ for Carbohydrates = 1.0
 C6H12O6 + 6O2       6H2O + 6CO 2

• RQ for fats = 0.71 (average)
             Energy needs
  Measurement of Energy Output

Indirect calorimetry
• RQ value can be used to find the amount
  energy produced per litre of oxygen
• Metabolic mix
               Energy needs
Measurement of Energy Output
Indirect calorimetry
• Respiratory Gas Analysis
     • Respirmeters
     • Direct of measurement of O2 and CO2

• Heart Rate Monitoring
     • Heart rate calibrated against oxygen utilisation
• Isotope Method
     • Labelled water (2H and 18O)
     • Difference of rates of loss of isotopes loss of CO2
What are the components of energy expenditure?

1:   Basal metabolic rate



  Energy Out: Basal Metabolism
• Largest daily energy output
• Definition: “the sum total of minimal activity of
  all tissue cells of the body under steady sate
• Men estimate: lbs body weight X 11
• Women estimate: lbs body weight X 10
• affected by
   – Muscle > Fat            Male > Female
   – Young > Old
   – Temperature: body and environment
          Basal Metabolic Rate
• BMR = number of calories would need daily
  simply to stay alive if were totally inactive, in bed,
  awake for 16 hours & slept for 8 hours
• Harris-Benedict Equation:
• Women: 661+(4.38 x weight in pounds)+(4.38 x
  height in inches)-(4.7 x age)=BMR
• Men: 67+(6.24 x weight in pounds)+(12.7 x height
  in inches)- (6.9 x age)=BMR
James & Schofield
        1) Basal Metabolic Rate
• 50-70% Energy Expenditure
• Maintain basic metabolic processes
    Cells     Muscles      Temperature regulation
•   Osmotic pumps
•   Protein synthesis
•   Heart
•   Respiratory system             10%
•   Digestive tract
•   Individual variation
•   Within individual variation
      Factors affecting BMR
• 1) Body Size & Composition
  – Lean tissue BMR
  – Body weight wt lean tissue (but also fat)
• 2) Age:
  – age Lean tissue
• 3) Sex: Men lean
• 4) Activity: Exercise lean tissue
      Factors affecting BMR
• 5) Growth BMR
  – Children, pregnancy
• 6) Fasting/starvation: BMR
• 7) Fever/stress BMR
• 8) Smoking/caffeine: BMR
2:    Energy Expenditure Component :




     Contribution to Total Energy
      2) Energy Out: Dietary

• Dietary thermogenesis
  – Energy to digest, absorb, metabolize food
  – About 10% of calories eaten
     2) Thermic Effect of Food

• 3-6 hours following ingestion
• ~10% energy intake
  – 2000 kcal diet = 200 kcal TEF
• Affected by:
  – Meal size/frequency
  – Composition: Protein > Carbs/fat
  – Genetics
3:   Components of Energy Expenditure

     Physical Activity

     Contribution to Total Expenditure:

4:   What about accounting for changes in energy expenditure
     due to injury or trauma?
3) Energy Out: Physical Activity

• Physical Activity affected by:
  – Intensity -- how vigorous
  – Time spent
  – Body weight
         3) Physical Activity
• Variable: 20-40%
• Working muscles require energy
  – Heart/lung extra energy
• Amt energy used depends on:
  – Muscle mass
  – Body weight
  – Activity nature & duration
 Activity Level and Metabolism
• Activity can account for 20-30% of
1. Sedentary = Multiplier 1.15 x BMR
2. Light activity (Normal Every day activities) =
   Multiplier 1.3 x BMR
3. Moderately Active(exercise 3-4 x’s week) =
   Multiplier 1.4 x BMR
4. Very Active (exercise more than 4 x’s week) =
   Multiplier 1.5 x BMR
5. Extremely Active (exercise 6-7 x’s week) =
   Multiplier 1.6 x BMR
 Activity Level and Metabolism
• If you change Light activity (Normal Every
  day activities) to Moderately Active(exercise 3-
  4 x’s week) daily caloric burning goes up 7.7%

• If you change Light activity (Normal Every
  day activities) to Very Active (exercise more
  than 4 x’s week) daily caloric burning goes up

• If you change Light activity (Normal Every
  day activities) to Extremely Active (exercise 6-
  7 x’s week) daily caloric burning goes up
Full thickness
Burns                 trauma           sepsis

  GI        Cardiac            Renal       Cancer
Injury, Trauma, Surgery

           Neurohormonal Activation of the Stress

                      Glucocorticoid & Catecholamine
                      Activation, Hi Glucagon:Insulin
                      Ratio, Growth Hormone Release

     Tachycardia, Tachypnea, Hyperglycemia,
     Mobilization of Body Fat, Massive Catabolism
     of Skeletal Muscle
In Critical Illness, Timing of Assessment is
Extremely Important!


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)
  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
                      distress, CHF, etc.
            Maintaining Body Composition:
          Fuel Utilization in Maintenance and Injury

Average Adult Composition
Water                         55

Protein                        19

Adipose Tissue                 19

CHO                            <1

Inorganic matter               7
                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.

             Fuel Sources During Exercise

Normal ADL        LIGHT        MODERATE     HEAVY
        Energy Requirements
• Difficult to estimate
• Direct measurement
  – Research
• Estimates from averages
  – Based on age/sex
  – Assume light/moderate activity
  – Estimate TEF
• We Need Energy for 3 Reasons:
  – 1) Basal metabolism
  – 2) Physical activity
  – 3) Dietary thermogenesis
• How many calories do you need?
  – Simple calculation
         1) Basal Metabolism
• Definition: Energy required to maintain
  normal body functions while at rest
• To estimate the calories you need for basal
  – For men: Multiply body weight (lbs) by 11
  – For women: Multiply body weight (lbs) by 10
       2) Energy for Physical Activity
                                     METABOLISM CALORIES
Inactive: sitting most of the day;
<2 hours moving about slowly or              30%

Moderate: sitting most of the
day; walking or standing 2-4                 50%
hours, no strenuous activity

Active: physically active for >4
hours a day; little sitting or               75%
standing; some strenuous activity
     3) Dietary Thermogenesis

• Definition: the energy expended during
  digestion of food
• It accounts for approximately 10% of the
  body's total energy need (basal needs and
  energy needs)
         Doing the Calculation
• Jane weighs 140 and is moderately active student
  (she goes to classes and goes to the gym 1hr/day)
• Basal needs: 140 * 10 = 1400
• Physical activity needs: 1400 * .50= 700
• So far she needs 2100 calories, but wait, she has
  to digest!
• 2100 * .10 = 210 calories
• Now, we add it up for her: 1400 + 700 + 210=
  2310 calories
• How many calories do you need???
             Energy Balance
• Balanced energy intake: not losing or
  gaining weight
• Negative energy balance (weight loss):
  energy intake < energy expended
• Positive energy balance (weight gain):
  energy intake > energy expended
         Hunger vs. Appetite
• Hunger: physical need for energy,
  accompanied with unpleasant symptoms
  such as weakness, stomach pains, irritability
• Appetite: desire to eat is driven by mental
• How do we define obesity?
  –By culture
  –By science
      Is Obesity an Epidemic?
• Prevalence in US: 33% of adults and 25%
  of children are obese (But according to
• Risks associated with obesity: diabetes,
  hypertension, stroke, heart disease, elevated
  total cholesterol, low HDL-cholesterol,
  certain types of cancer, gallbladder disease
         What Causes Obesity
• 3 major factors contribute to the development of
   – 1) Genetic background
      • Heredity may account for approx. 25-40% of obesity
        but this is very poorly understood
      • Effects on metabolism (rare); traits that predispose
   – 2) Dietary intake

   – 3) Physical activity
         Measuring Body Fatness
•   Weight-for-Height tables:
     – Dietary Guidelines for Americans
     – Metropolitan Life Insurance Company (allows for
       increased weight with age)
     – Limitations: not based on percentage body fat
•   Body Mass Index (BMI)- widely used
     – Calculated by dividing body weight (in kg) by height
       (in meters) squared
         • 19-25 is considered acceptable
         • overweight is btw. 25-30
         • > 30 obesity
 Some Methods for Assessing Body Fat:

• Scale weighing doesn't distinguish between
  lean body mass and body fat
   –   Skinfold thickness measurements
   –   Bioelectrical impedance
   –   Underwater weighing
   –   Magnetic resonance imaging (MRI)
   –   CAT scans
   –   Ultrasound
   –   Total body electrical conductivity
   –   Magnetic resonance spectroscopy
        We Do Need Body Fat
• For survival we need:
   – 3-5% for men
   – 10-12% for women
• Low body fat associated with
   –   Delayed physical maturation during adolescence
   –   Infertility
   –   Accelerated bone loss
   –   Symptoms of starvation
         Role of Body Fat:
– Makes hormones
– Component of every type of body cell
– Cushions internal organs
– This fat is not available for energy
  Location of Body Fat is Important to Health

• Central obesity is associated with more
  health risks than lower obesity
• Assessing Body Fat Distribution:
   – Waist to hip ratio
      • More than .80 in women and .95 in men indicate
        central body fat distribution
   – Waist circumference
      • Over 40" (102 cm) in men (increased risk for
        health problems)
      • Over 35" (88 cm) in women
                 Realities of Obesity

• Myth: any individual can get to any body weight
  if they diet and exercise enough
• People do come in different shapes and sizes and
  people should come in different shapes and sizes
• From a health perspective, the goal of obesity
  prevention and treatment should be for people to
  eat a health promoting diet, get regular exercise,
  and pay attention to hunger and satiety cues
    – What are the barriers with this goal?????
Body Composition
              Body Weight
• Fat Mass + Fat Free Mass
• FFM: muscle, lean tissue, bone, water
• Diseases associated with:
  – Excessive fat mass
  – Depleted fat mass
  – Depleted FFM
          Body Weight
• Body weight = Fat + FFM
  – Not % fat % FFM
Healthy Body Weight
• Weight associated lowest mortality
• Techniques for Assessing body weight
  – Life Insurance Tables
  – Relative weight
  – Body Mass Index
• Life Insurance Tables
  – Rarely used research/clinical practice
• Relative weight
  – Actual weight/desirable weight
  – 110-120%: overweight
  – 120-130% obese
• Disadvantages relative weight
  – Desirable difficult to define
  – Not sex specific
  – Not adjusted for age
Body Mass Index (BMI)

       Weight (kg)            Weight (lb)
 BMI =
       Height (m2)            Height (in2)
                                                     X 705

   Classification     BMI (kg/m2)       Risk co-morbidity
  Normal values       18.524.9            Average
  Overweight          25
  Pre-obesity         2529.9              Increased
  Obesity class I     30.034.9            Moderate
  Obesity class II    35.039.9            High
  Obesity class III   40.0               Very High
                                  World Health Organization,
 Limitations of BMI

Both men have a BMI of 31
Find % body fat by: Underwater

• Measures
  subcutaneous fat

• Accuracy depends
  on caliper skill
Other High Tech Methods
            • Bioelectrical
              Impedance BMI
            • Magnetic
              Resonance Imaging
            • “Bod-Pod”
              measures air
        Bioelectrical Impedance
•   Estimation of body composition
•   Most used in clinical practice
•   Based on electrical conduction through organism
•   At higher frequencies (eg 50 kHz) resistance of
    cell membranes reduced so that current penetrates
    both extra- and intracellular fluids
•   Bio impedance is a reliable prediction of the
    body‟s main conduction material : water
•   73.2% FFM consists of water and total FM + FFM
    = total body weight
•   Electrodes placed on dominant side of body; legs
    apart and not in contact
•   More accurate in obese women than DEXA
   Fat intake  but Overweight 


1 lb (0.4kg) body fat =~ 3500 kcal
Energy Balance
• Positive - Gain 1 lb - eat 3,500 kcal more
  than need
• Negative -Lose 1 lb - eat 3,500 kcal less
  than need
• If energy bal = - 500 kcal / day
  3500/500 = 7 days to lose 1 lb
• Best to combine with physical activity, e.g.,
  mile walk = - 100 kcal
    What happens in weight loss?
•  Water
•  Fat
•  Muscle mass
• May  Bone density
• Gradual weight loss minimizes loss of
  muscle & bone
• Drastic methods: fasting, surgery,
• Other methods: diets, pills
  Body fat location is important

• Apple = Abdomen
• Pear =
   Hips & thighs
• Apple -> risk of heart
• waist/hip ratio:
   >0.8 F, > 0.95 M
  indicates apple shape
                         Assessing obesity:
             bmi, waist circumference and disease risk

                                                                Disease Risk Relative to Normal
                                                                Weight and Waist Circumference
                                                                       Men <102 cm                    Men >102 cm
      Category                                 BMI                     Women <88 cm                   Women >88 cm

  Underweight                               <18.5                                —                        —
  Normal*                               18.5-24.9                                —                        —
  Overweight                            25.0-29.9                        Increased                       High
  Obesity                               30.0-34.9                          High                       Very high
                                        35.0-39.9                        Very high                    Very high
  Extreme obesity                             >40                   Extremely high Extremely high
*An   increased waist circumference can denote increased disease risk even in persons of normal weight.

Adapted from Clinical guidelines. National Heart, Lung, and Blood Institute Web site. Available at: Accessed July 31, 1998.
• Correlates with body fat content
• European Origin
  –   Asian: healthy weight <23.5
  –   Polynesian: healthy weight 18.5-26
  –   Elderly: healthy weight up to 27
  –   Requires further research
• Not suitable for athletes
     Body Fat Distribution
• disease risk/mortality with excessive body
• „Healthy‟ % body fat
  – 12-20% Men          20-30% Women
• Fat distribution associated disease risk
  – Abdominal fat risk
  – Lower body fat: no increase risk
• Central Obesity: Abdominal fat
  –  prevalence Men, postmenopausal women
• Measures of Central Adiposity
• 1) Waist Circumference
  – > 88 cm women, 102cm men
• 2) Waist:Hip Ratio
  – >0.8 women, 0.95 men
• 3) Fat fold measures
  – Training required
•   Prevalence increasing
•   Serious health concern
•   body weight 10% significant health risk
•   Prevalence obesity increases
    – Age
    – Lower socio-economic status
    – Women (USA)
• 0.5kg fat stores ~ 4500 kcals
• Recommended weight loss: 0.5kg/wk max
    – Not greater than 1kg/wk
•    intake by ± 600 kcals
•   Slow reduction: decreased loss lean tissue
•   Rapid loss: Large loss fluids
•   Long term: 75% fat loss, 25% lean loss
           Weight Control
• Case Study
• <5% US population
• Causes:
  – Hunger, illness, appetite, psychological traits,
• If malnourished weight gain nec
  – 1lb/month
  – 750-800kCals
  – Establish new eating habits
        Weight Gain Strategies
• Energy dense foods
    – Whole milk not skim
•   Regular meals
•   Large portions
•   Extra snacks
•   High energy beverages
•   Exercise: add lean muscle
    Anorexia Nervosa: definition
•   Starvation intentional
•   Fear of fatness
•   Significant weight loss
•   altered body image
•   Bizarre food behavior
•   Amenorrhea, delayed menses
• Refusal maintain body weight
• Intense fear weight gain/fatness
• Undue influence body weight/shape self
• Amenorrhea or delayed menses
  – 3 consecutive periods
• 2 types
• Restricting type
  – No regular binge eating/purging
• Binge eating/purging
  – Regular binge eating/purging
•   Inc dramatically
•   2-5% adolescent & young women
•   5% mortality rate
•   Upper SES
•   Family history
•   Stress/perfectionist
       Physical consequences
• PEM: similar to Marasmus
    – LBM BMR
• Decreased growth
• Irregular heart beat, blood pressure
• Electrolyte imbalance
• brain tissue, impaired immune system,
  anemia, digestive functioning
• Development body hair
• Multidisciplinary approach
  – Involve family
• Restore nutritional status
  – Add 200kcal/week
  – Supplements initially
• Psychological treatment
  – Reward eating not weight
• Exercise education
    Bulimia Nervosa: diagnosis
• Recurrent episodes binge eating
  – Large amount food short time
  – Sense of lack control
• Inappropriate compensation
• 2/week for 3 months
• Self esteem unduly influenced body shape
• More prevalent AN
• More common in men than AN
• Single white female
  – Well educated
  – Close to ideal body weight
• Family history
  – Obesity, depression, abuse, conflicts, high
    Physical consequences
• immune system
• Fluid & mineral imbalance
• Abnormal heart rhythms, kidney damage
• Damage pharynx, esophagus, salivary
  glands, teeth
• Calloused hands
•   Avoid finger foods
•   Prolong eating time, add bulk
•   Satisfy hunger
•   Plan meals, snacks
•   Depression, additive behavior therapy
•   Goal: Weight maintenance
    – Avoid cyclic weight,
Binge Eating Disorder: BED
• Binging without purging
• Consume less during binge than BN, less
  restraint following
• Associated with
  – Self loathing, depression, anxiety
• Treatment: psychological counseling
Female Athlete Triad
        Eating disorder
       •Restrictive dieting,
        •over exercising,
          •lack body fat


   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
       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:
           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.
   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
      Metabolic Adaptations to Fasting/Starvation:

Advantages                                Disadvantages

 Energy Expenditure                       Wasting of
                                            muscle mass
 Body Temperature                         Decreased
Enhanced Survival                           competence