Nutrition and Metabolism

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%

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)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 derivingphysiologic 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. 25-40% 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• 19-25 is considered acceptable

• overweight is btw. 25-30

• > 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 18.524.9 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

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.

• NB: Patients with advanced cancer or AIDS are malnourished and this condition is called CachexiaCachexia.