Nutrition and Metabolism

1) Basal Metabolic Rate 50-70% Energy Expenditure Maintain basic metabolic processes CellsMusclesTemperature regulation Growth Osmotic pumps Protein synthesis Heart Respiratory system Digestive tract 10%

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 Out: Dietary Thermogenesis 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 ( total energy expenditure) Affected by: –Meal size/frequency –Composition: Protein > Carbs/fat –Genetics

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 Energy used depends on: –Muscle mass –Body weight –Activity nature & duration

Maintaining Body Composition: Fuel Utilization in Maintenance and Injury Average Adult Composition % (w/w) Water55 Protein19 Adipose Tissue19 CHO<1 Inorganic matter 7

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!!!

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)

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 stimuli

Obesity 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 Risks associated with obesity: diabetes, hypertension, 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 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

Measuring Body Fatness Body Mass Index (BMI)- widely used –Calculated by dividing body weight (in kg) by height (in meters) squared is considered acceptable overweight is btw > 30 obesity

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

Role of Body Fat: –Makes hormones –Component of every type of body cell –Cushions internal organs

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

Body Composition

Body Weight Fat Mass + Fat Free Mass FFM: lean tissues, bone, water Diseases associated with: –Excessive fat mass –Depleted fat mass –Depleted FFM

 Body Mass Index (BMI) World Health Organization, 1998 Normal values 18.5  24.9Average Overweight  25 Pre-obesity 25  29.9Increased Obesity class I 30.0  34.9Moderate Obesity class II 35.0  39.9High Obesity class III  40.0  Very High Classification BMI (kg/m 2 ) Risk co-morbidity Weight (kg) Height (m 2 ) BMI = Weight (lb) Height (in 2 ) X 705

Find % body fat by: Underwater Weighing

Skinfold Measures subcutaneous fat Accuracy depends on caliper skill

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

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

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

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. CachexiaNB: Patients with advanced cancer or AIDS are malnourished and this condition is called Cachexia.