Energy BalanceBody Composition

Gaining & Losing weight

• Whether a person gains or loses weight depends on:– Energy intake vs. energy expenditure– Genetic factors– Childhood weight– Behavioral factors– Social factors

Energy Balance

• Energy balance– Occurs when energy intake = energy

expenditure– Energy intake = kcal from food– Energy expenditure = energy

expended at rest + during physical activity

Energy Expenditure

• BMR• Physical activity• Thermic Effects

– Cost of food processing

Energy Balance

• Basal Metabolic Rate (BMR)– Energy expended to maintain basal, or

resting, functions of the body• highest proportion of total energy expenditure

– More lean tissue increases your BMR– BMR decreases with age

• ~3-5% per decade after 30

– Estimating BMR• body weight (kg) * 1.0 kcal/kg/hour

So, obese people have lower BMR, right?

Factors affecting BMR

Energy Balance

• Thermic Effect of Food (TEF)– Energy expended to process food– ~5-10% of total kcal of the meal

• 500 kcal meal costs 25 - 50 kcal to process

– Fats require little energy to digest, transport & absorb

– Proteins & Carbs require more

Physical Activity

• 20-35% of total energy output• Includes everything above basal level

– Sitting, standing, walking

• Moving large muscles requires more Energy

• Calculating Energy expenditure:– Energy Cost (kcal/kg/min) * Time (min)

• Do a couple

Genetic factors• Different hypotheses explain the impact

of genetics on body fat– Thrifty Gene Theory– Set-point Theory– Leptin Theory

Thrifty Gene Theory• H1: individuals with the gene use less

energy (at all times) than people who do not possess the gene– More efficient fat storage– Lower metabolic rates

• Evolutionary story: Protection against starvation during lean times

• Applied to American Indian populations with high rates of obesity & diabetes

– Evidence: No direct; little indirect

Set-Point Theory• H1: Body is tuned to maintain weight

within a narrow range, or “set-point”• Evidence:

– Body appears to maintain weight @ present level

– Rebound weight gain among dieters– Occasional over-eating often does not

result in weight gain– Can change set point through consistent,

long term changes in diet & exercise

Leptin Theory

• Leptin: hormone produced by adipose cells; goes systemic– Binds to neurons in “satiety center” in

brain; inhibits neurons that stimulate feelings of hunger

– Increased production reduces food intake, body weight and body fat

Childhood weight• Environmental factors in childhood

influence– Food choices– Activity levels– Later adult behaviors

• Childhood overweight increases the risk of heart disease and premature death as an adult

Behavioral Choices

• Food Choices – Composition of diet should remain

balanced– Overeating dietary fat increases obesity

faster than overeating carbs or proteins– Why?

• Less energy required to digest fats than other two

• More easily stored as adipose tissue…no conversion necessary

Behavioral Choices

• Hunger vs. Appetite– Appetite = psychological desire to eat;

cause overeating– “Satiety mechanism” malfunction

• Hormone or sensory receptor malfunction• Increase or decrease satiety

Social Factors

• Social factors influence our diet:– Family or cultural traditions– Holidays and celebrations– Easy access to high-fat foods– Less physically active lifestyles– Societal expectations of the “perfect”

body

How many kcals do we need?

• Manual calculation:– BMR (women) = body weight (kg) * 0.9 kcal/

kg/hour– BMR (men) = body weight (kg) * 1.0 kcal/ kg/hour

• 77.3 kg * 1 * 24 = 1855 kcal

– Activity = some percentage of BMR; Ex: 70%• 1855 kcal * 0.70 = 1299 kcal• 1855 + 1299 = 3154 kcal

• How many are you eating? Recall:– Fats: 9 kcal/gram– Carbs: 4 kcal /gram– Proteins: 4 kcal/gram

What is a healthful body weight?

• Appropriate for your age• Maintained without constant dieting• Is acceptable to you• Based on family history of body shape

and weight• Promotes healthful eating habits and

allows for regular physical activity

Evaluating body weight

• Actual weight is not the only factor to consider

• Determining if a person’s body weight is healthful should include:

1. Determining the Body Mass Index (BMI)2. Measuring body composition3. Assessing the pattern of fat distribution

Evaluating body weight

• Body Mass Index = BMI– BMI = weight (kg) / height (m)2

– BMI values below 18.5 or above 30 have increased risks of health problems

Excess Death among overweight people

Declining weight of Miss America

Distribution of Body Weights in U.S. Adults

Obesity(BMI 30–39.9)

Underweight(BMI <18.5)

Overweight(BMI 25–29.9)

Healthy weight(BMI 18.5–24.9)

Extreme obesity(BMI >40)_

Achieving & maintaining healthy weight

• Healthful weight change requires– Gradual change in energy intake– Regular and appropriate physical

exercise– Application of behavior modification

techniques

Losing weight

– Follow recommended serving sizes– Reduce intake of high-fat and high-

energy foods (~20%)– Regular physical exercise (of ANY kind will do,

but which kinds preferentially burn fat?)

• Increase energy expenditure• Increase BMR

Gaining weight– Eat 500 to 1,000 extra kcal/day– Eat frequently throughout the day– Maintain a balanced diet; keep fat intake

to 25-30% of total energy intake– Avoid tobacco products

• depresses appetite; increase BMR

– Regular exercise with resistance training• Promotes conversion of calories to lean

muscle rather that fat

Gaining weight

• Supplements?• Studies continue to show no effect of

AA and protein supplements:– No gains in muscle mass and strength, nor

in performance– Including androstenedione (Mark McGuire)

• Some effects of this supplement are increased LDL:HDL levels (why bad?) & mood disturbances

• Also, those unfortunate (if you’re a male) feminizing characteristics

Disorders & Energy intake

• Underweight: having too little body fat to maintain health– BMI less than 18.5 kg/m2

– Increases risk of infection and illness• Overweight:

– BMI of 25 - 29.5 kg/m2

– Some health risks; most importantly, adopt healthier lifestyle to avoid becoming obese

Obesity & Morbid obesity• Obesity: Having excess body fat that

adversely effects health• BMI 30 - 39.9 kg/m2

• BMI > 40 kg/m2 = morbidly obese– Body weight exceeds 100% of normal

• Morbid obesity: body weight exceeding 100% of normal, creating a very high risk for serious health complications

Increase in childhood obesity

Critical periods

• Weight gain in specific life stages have strong effects on weight later in life.

• Weight gain in these periods increase risk of adult obesity & related diseases– Gestation & early infancy– Ages 5-7– Adolescence