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Lesson 2 : Role of Metabolism in Nutrition

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1 Lesson 2 : Role of Metabolism in Nutrition

2 Metabolism 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

3 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.

4 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 precursors Energy-rich molecules are used to promote these reactions

5 Examples of each type of metabolism:
Anabolic Pathways Catabolic Pathways Protein Biosynthesis Glycolysis Glycogenesis 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

6 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 needs. Supplies roughly 1 x 106 kcals/ year

7 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)

8 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)

9 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 = kJ : Protein: 17 kJ or 4 kcal/g CHO: 17 kJ or 4 kcal/g Fat: 37 kJ or 9 kcal/g

10

11 Energy needs Measurement of Energy Intake Metabolic Energy Yields

12 Average Energy Needs: European text: 100 kJ/ day x BW in kg or 24 kcal/day x BW in kg American Biochem text: kJ/ kg 31-44 kcal/kg

13 Conversion Efficiency: Food to Usable Energy
40% used to make high energy phosphate bonds 60% “lost” (?) as heat

14 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

15 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

16 Bomb Calorimeter measures heat produced when food is burned

17 Text view of bomb calorimeter

18 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

19 Energy needs Measurement of Energy Intake
% Energy from carbohydrates, protein and fat

20 Energy Balance: Input vs Output

21 Energy Balance Energy In = Energy Out Energy In > Energy Out
Weight Maintenance Energy In > Energy Out Weight Gain Energy In < Energy Out Weight Loss

22 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”

23 Energy In Food and Beverages
Food composition tables Bomb Calorimetry Complex social, environmental, physiological control

24 Energy Out Energy of food = Body Energy = ATP Energy out:
Overall efficiency 25%, 75% released heat Energy out: 3 main components: Basal Metabolic Rate Thermic Effect Food Physical activity

25 BMR > Activity > Dietary Thermogenesis

26 Energy needs Measurement of Energy Output Energy Output
Energy of food ATP + Heat Loss 50% efficiency ATP “Work “+ Heat Loss “Work “ Heat

27 Energy needs Measurement of Energy Output Energy Output Two methods
direct calorimetry indirect calorimetry Measurement of heat Measurement of energy used

28 Energy needs Measurement of Energy Output direct calorimetry
Measurement of heat loss

29 Energy needs Measurement of Energy Output Indirect calorimetry
Utilisation of oxygen Oxygen consumption is proportional to ATP synthesis Use oxygen consumption to determine heat production

30 Energy needs Measurement of Energy Output Indirect calorimetry
Glucose oxidation Starch oxidation 6H2O + 6CO 2 C6H12O6 + 6O2 + 15.5 kJ/g of energy 5nH2O + 6nCO 2 (C6H12O5)n + 6nO2 + 17 kJ/g of energy

31 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

32 Energy needs Measurement of Energy Output Indirect calorimetry
Respiratory quotient (RQ) CO 2 Produced / O 2 Consumed RQ for Carbohydrates = 1.0 RQ for fats = 0.71 (average) C6H12O6 + 6O2 6H2O + 6CO 2

33 Energy needs Indirect calorimetry Measurement of Energy Output
RQ value can be used to find the amount energy produced per litre of oxygen consumed Metabolic mix

34 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

35 What are the components of energy expenditure?
1 : Basal metabolic rate Definition: Determinants: Calculation:

36 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 conditions” 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

37 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

38 James & Schofield

39 1) Basal Metabolic Rate 50-70% Energy Expenditure
Maintain basic metabolic processes Cells Muscles Temperature regulation Growth Osmotic pumps Protein synthesis Heart Respiratory system Digestive tract Individual variation Within individual variation 10%

40 Factors affecting BMR 1) Body Size & Composition 2) Age:
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

41 Factors affecting BMR 5) Growth BMR 6) Fasting/starvation: BMR
Children, pregnancy 6) Fasting/starvation: BMR 7) Fever/stress BMR 8) Smoking/caffeine: BMR

42 2 : Energy Expenditure Component :
THERMIC EFFECT OF FOOD Definition: Determinants: Contribution to Total Energy Expenditure:

43 2) Energy Out: Dietary Thermogenesis
Energy to digest, absorb, metabolize food About 10% of calories eaten

44 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

45 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?

46 3) Energy Out: Physical Activity
Physical Activity affected by: Intensity -- how vigorous Time spent Body weight

47 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

48 Activity Level and Metabolism
Activity can account for 20-30% of metabolism Sedentary = Multiplier 1.15 x BMR Light activity (Normal Every day activities) = Multiplier 1.3 x BMR Moderately Active(exercise 3-4 x’s week) = Multiplier 1.4 x BMR Very Active (exercise more than 4 x’s week) = Multiplier 1.5 x BMR Extremely Active (exercise 6-7 x’s week) = Multiplier 1.6 x BMR

49 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 23% If you change Light activity (Normal Every day activities) to Extremely Active (exercise 6-7 x’s week) daily caloric burning goes up 38.5%

50 Who Are The Critically Ill?
Full thickness Burns trauma sepsis Who Are The Critically Ill? GI Cardiac Renal Cancer

51 Injury, Trauma, Surgery Neurohormonal Activation of the Stress Response Glucocorticoid & Catecholamine Activation, Hi Glucagon:Insulin Ratio, Growth Hormone Release Tachycardia, Tachypnea, Hyperglycemia, Mobilization of Body Fat, Massive Catabolism of Skeletal Muscle

52 Metabolism in critical injuries goes through at least three
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)

53 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 distress, CHF, etc.

54 Fuel Utilization in Maintenance and Injury Average Adult Composition %
Maintaining Body Composition: Fuel Utilization in Maintenance and Injury Average Adult Composition % (w/w) Water Protein 19 Adipose Tissue 19 CHO <1 Inorganic matter 7

55 Recommended Fuel Sources
(% of kcal) Source % of kcals DRVs Atwater* Fat Protein CHO *W.O. Atwater (1894), USDA Scientist credited with deriving physiologic energy values of pro, CHO, fat. PROGRESS!!!

56 Fuel Sources During Exercise
Normal ADL LIGHT MODERATE HEAVY

57 Energy Requirements Difficult to estimate Direct measurement
Research Estimates from averages Based on age/sex Assume light/moderate activity Estimate TEF

58 Energy We Need Energy for 3 Reasons: How many calories do you need?
1) Basal metabolism 2) Physical activity 3) Dietary thermogenesis How many calories do you need? Simple calculation

59 1) Basal Metabolism Definition: Energy required to maintain normal body functions while at rest To estimate the calories you need for basal metabolism For men: Multiply body weight (lbs) by 11 For women: Multiply body weight (lbs) by 10 8

60 2) Energy for Physical Activity
ACTIVITY LEVEL PERCENTAGE OF BASAL METABOLISM CALORIES Inactive: sitting most of the day; <2 hours moving about slowly or standing 30% Moderate: sitting most of the day; walking or standing 2-4 hours, no strenuous activity 50% Active: physically active for >4 hours a day; little sitting or standing; some strenuous activity 75% 8

61 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)

62 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: = 2310 calories How many calories do you need??? 8 - Say: If I told you what a man or woman weighs and their level of physical activity you should be able to calculate how many calories they need for one day.

63 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 8

64 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 stimuli

65 Obesity By culture By science How do we define obesity? 9
-Say can we really separate culture and science? Not entirely, no. Researchers and anyone in the health field will apply their own societal beliefs to what defines obesity and health consequences thereof. Consider an individual who weighs 400 pounds and undergoes stomach stapling. Now, from a medical perspective that may reduce her risk of disease, but a physician from another culture may say that that is a far too invasive procedure and will harm that individual’s mental health.

66 Is Obesity an Epidemic? Prevalence in US: 33% of adults and 25% of children are obese (But according to whom????) Risks associated with obesity: diabetes, hypertension, stroke, heart disease, elevated total cholesterol, low HDL-cholesterol, certain types of cancer, gallbladder disease 9 -Is obesity itself an epidemic or have Americans developed some unhealthy behaviors over the years? Ask them what they think about this -Focusing just on the obesity will be a waste of time, because people have a very, very hard time losing weight. Diets have a 95% failure rate. We are very, very far from drug that can reduce obesity over the long term without a lot of side effects. Not a solution for the general public. -What about the fact that people come in all shapes and sizes? People should come in all shapes and sizes. But there’s a balance between accepting people of all sizes and encouraging weight control. -can talk about my research with diabetes -we can not underestimate the emotional damage, I.e. poor self esteem, depression, that accompanies obesity, but again, this is a cultural facor and the others are actual risks.

67 What Causes Obesity 3 major factors contribute to the development of obesity 1) Genetic background Heredity may account for approx % of obesity but this is very poorly understood Effects on metabolism (rare); traits that predispose (common) 2) Dietary intake 3) Physical activity 9 -Explain that I disagree with the genetic background one; eating behaviors will outweigh genes. Plus, you really can't do anything about genes. All the work that's being done is being done with rats. We are a very long way off from treating genetic traits of obesity, and I'm not convinced that this will ever be sucessful. You have to take in more calories than you expend, that is the one machine like trait of humans. We run on fuel and when we get extra we store it, and when we don't get enough, we burn it. That doesn't mean that all obese people overeat, because their energy output may be very slow.

68 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 > 30 obesity 9 -Photocopy table 9.1 and show as an example of a weight for height table. Say, really not very accurate -Photocopy Met. Life. Ins. table and show -Say about BMI: You will see this more and more. It has become the more accepted standard for obesity assessment. Note: individual's with BMI's over 30 are necessarily at risk for disease. Many other factors are important, like physical activity levels, smoking, stress, diet, alcohol intake, heredity factors

69 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 9 -Say: If you've considered getting any of these done, I would read more about them on page 9-6 of textbook. -Say about point one: You'll also see this method at gyms and sometimes at doctor's offices where calipers are used to measure body fatness in certain area's of the body. These really aren't too accurate because it is very difficult to take the reading correctly.

70 We Do Need Body Fat For survival we need: Low body fat associated with
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

71 Role of Body Fat: Makes hormones Component of every type of body cell
Cushions internal organs This fat is not available for energy

72 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 9 -Show Illustration 9.2 and 9.3 -Say: Picture 9.2 is silly but it has been found that central obesity, the apple shape, is associated with increased risk for diabetes, hypertension, high blood cholesterol, and heart disease -don't need to know the numbers but know that these two methods are commonly used to assess body fat distribution

73 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????? -but getting to this behavior modification therapy isn’t easy. What of these three factors, changing the diet, exercising, and eating less, do you think is most easily done? Exercise I think.

74 Body Composition

75 Body Weight Fat Mass + Fat Free Mass
FFM: muscle, lean tissue, bone, water Diseases associated with: Excessive fat mass Depleted fat mass Depleted FFM

76 Body Weight Body weight = Fat + FFM Healthy Body Weight
Not % fat % FFM Healthy Body Weight Weight associated lowest mortality Techniques for Assessing body weight Life Insurance Tables Relative weight Body Mass Index

77 Disadvantages relative weight
Life Insurance Tables Rarely used research/clinical practice Relative weight Actual weight/desirable weight %: overweight % obese Disadvantages relative weight Desirable difficult to define Not sex specific Not adjusted for age

78 Body Mass Index (BMI) X 705 Weight (kg) Weight (lb) BMI = Height (m2)
World Health Organization, 1998 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 Weight (kg) Height (m2) BMI = Weight (lb) Height (in2) X 705 Classification BMI (kg/m2) Risk co-morbidity

79 Limitations of BMI Both men have a BMI of 31

80 Find % body fat by: Underwater Weighing

81 Skinfold Measures subcutaneous fat Accuracy depends on caliper skill

82 Other High Tech Methods
Bioelectrical Impedance BMI Magnetic Resonance Imaging MRI “Bod-Pod” measures air displacement

83 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

84 Fat intake  but Overweight 
Total calories Physical activity

85 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 = kcal / day /500 = 7 days to lose 1 lb Best to combine with physical activity, e.g., mile walk = kcal

86 What happens in weight loss?
 Water  Fat  Muscle mass May  Bone density Gradual weight loss minimizes loss of muscle & bone Drastic methods: fasting, surgery, liposuction Other methods: diets, pills

87 Body fat location is important
Apple = Abdomen Pear = Hips & thighs Apple -> risk of heart disease waist/hip ratio: >0.8 F, > 0.95 M indicates apple shape

88 Assessing obesity: bmi, waist circumference and disease risk
Disease Risk Relative to Normal Weight and Waist Circumference Men <102 cm Women <88 cm Men >102 cm Women >88 cm Category BMI Underweight Normal* Overweight Obesity Extreme obesity <18.5 >40 Increased High Very high Extremely high High Very high Very 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.

89 Correlates with body fat content European Origin
Asian: healthy weight <23.5 Polynesian: healthy weight Elderly: healthy weight up to 27 Requires further research Not suitable for athletes

90 Body Fat Distribution disease risk/mortality with excessive body fat
‘Healthy’ % body fat 12-20% Men % Women Fat distribution associated disease risk Abdominal fat risk Lower body fat: no increase risk

91 Central Obesity: Abdominal fat Measures of Central Adiposity
 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

92 Obesity Prevalence increasing Serious health concern
body weight 10% significant health risk Prevalence obesity increases Age Lower socio-economic status Women (USA)

93 Recommended weight loss: 0.5kg/wk max  intake by ± 600 kcals
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

94 Weight Control Case Study

95 Underweight <5% US population Causes:
Hunger, illness, appetite, psychological traits, hereditary… If malnourished weight gain nec 1lb/month kCals Establish new eating habits

96 Weight Gain Strategies
Energy dense foods Whole milk not skim Regular meals Large portions Extra snacks High energy beverages Exercise: add lean muscle

97 Anorexia Nervosa: definition
Starvation intentional Fear of fatness Significant weight loss altered body image Bizarre food behavior Amenorrhea, delayed menses

98 Diagnosis Refusal maintain body weight
Intense fear weight gain/fatness Undue influence body weight/shape self esteem Amenorrhea or delayed menses 3 consecutive periods

99 2 types Restricting type Binge eating/purging
No regular binge eating/purging Binge eating/purging Regular binge eating/purging

100 Demographics Inc dramatically 2-5% adolescent & young women
5% mortality rate Upper SES Family history Stress/perfectionist

101 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

102 Treatment Multidisciplinary approach Restore nutritional status
Involve family Restore nutritional status Add 200kcal/week Supplements initially Psychological treatment Reward eating not weight Exercise education

103 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

104 Demographics 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 expectations.

105 Physical consequences
immune system Fluid & mineral imbalance Abnormal heart rhythms, kidney damage UTI Damage pharynx, esophagus, salivary glands, teeth Calloused hands

106 Treatment Avoid finger foods Prolong eating time, add bulk
Satisfy hunger Plan meals, snacks Depression, additive behavior therapy Goal: Weight maintenance Avoid cyclic weight,

107 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

108 Female Athlete Triad Eating disorder Osteoporosis Amenorrhea
Restrictive dieting, over exercising, lack body fat Amenorrhea hormones Osteoporosis Bone mineralization

109 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

110 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:

111 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.

112 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

113 Metabolic Adaptations to Fasting/Starvation:
ADVANTAGES & DISADVANTAGES Advantages Disadvantages Energy Expenditure Wasting of muscle mass Body Temperature Decreased immune Enhanced Survival competence


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