nutrition and metabolism. 1) basal metabolic rate 50-70% energy expenditure maintain basic metabolic...
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Nutrition and Metabolism
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1) Basal Metabolic Rate• 50-70% Energy Expenditure• Maintain basic metabolic processes
Cells Muscles Temperature regulationGrowth
• Osmotic pumps• Protein synthesis• Heart• Respiratory system• Digestive tract
10%
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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
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Factors affecting BMR
• 5) Growth BMR– Children, pregnancy
• 6) Fasting/starvation: BMR
• 7) Fever/stress BMR
• 8) Smoking/caffeine: BMR
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2) Energy Out: Dietary Thermogenesis
• Dietary thermogenesis– Energy to digest, absorb, metabolize food
– About 10% of calories eaten
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2) Thermic Effect of Food
• 3-6 hours following ingestion
• ~10% energy intake– 2000 kcal diet = 200 kcal TEF ( total energy
expenditure)
• Affected by:– Meal size/frequency– Composition: Protein > Carbs/fat– Genetics
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3) Energy Out: Physical Activity
• Physical Activity affected by:
– Intensity -- how vigorous
– Time spent
– Body weight
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3) Physical Activity
• Variable: 20-40%
• Working muscles require energy– Heart/lung extra energy
• Energy used depends on:– Muscle mass– Body weight– Activity nature & duration
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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 <1
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 derivingphysiologic energy values of pro, CHO, fat.
PROGRESS!!!
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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)
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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
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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
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Obesity
• How do we define obesity?
–By culture
–By science
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Is Obesity an Epidemic?
• Prevalence in US: 33% of adults and 25% of children are obese
• Risks associated with obesity: diabetes, hypertension, heart disease, elevated total cholesterol, low HDL-cholesterol, certain types of cancer, gallbladder disease
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What Causes Obesity
• 3 major factors contribute to the development of obesity– 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 (common)
– 2) Dietary intake
– 3) Physical activity
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Measuring Body Fatness• 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
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We Do Need Body Fat
• For survival we need:– 3-5% for men
– 10-12% for women
• Low body fat associated with– Infertility
– Accelerated bone loss
– Symptoms of starvation
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Role of Body Fat:
– Makes hormones
– Component of every type of body cell
– Cushions internal organs
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Location of Body Fat is Important to Health
• Central obesity is associated with more health risks than peripheral 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
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Body Composition
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Body Weight
• Fat Mass + Fat Free Mass
• FFM: lean tissues, bone, water
• Diseases associated with:– Excessive fat mass– Depleted fat mass– Depleted FFM
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Body Mass Index (BMI)
World Health Organization, 1998
Normal values 18.524.9 Average
Overweight 25Pre-obesity 2529.9 IncreasedObesity class I 30.034.9 ModerateObesity class II 35.039.9 HighObesity class III 40.0Very High
Classification BMI (kg/m2) Risk co-morbidity
Weight (kg)
Height (m2)BMI =
Weight (lb)
Height (in2) X 705
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Find % body fat by: Underwater Weighing
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Skinfold
• Measures subcutaneous fat
• Accuracy depends on caliper skill
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Other High Tech Methods
• Bioelectrical Impedance BMI
• Magnetic Resonance Imaging MRI
• “Bod-Pod” measures air displacement
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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
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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
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Undernutrition• 1) Marasmus : occurs in both adults and children.
• 2)Kwashiorkor: Only affect children in developing countries. Affect only children and characterized by fluid retention and edema. It is defined as a state of extreme emaciation ( Prolonged negative energy). Not only body fats exhaustion but wastage of muscle proteins as well as proteins in heart, liver and kidney with reduction in protein synthesis results in impaired immune response and more risk for infections.
• NB: Patients with advanced cancer or AIDS are malnourished and this condition is called CachexiaCachexia.