Obesity

Energy Balance

• Energy balance is the relationship between energy intake and energy expenditure.

• Energy Intake = Energy Expenditure: Weight is maintained.

• Energy Intake > Energy Expenditure: Weight gain occurs (positive energy balance).

• Energy Intake < Energy Expenditure: Weight loss occurs (negative energy balance).

Components of Total Energy Expenditure

• Total energy expenditure is the energy the body uses for basic functions, movement, and activity.

• It comprises three main components:

  • Basal Metabolic Rate (BMR)

  • Physical Activity

  • Thermic Effect of Food

Basal Metabolic Rate (BMR)

• BMR is the minimum energy needed to keep a resting, awake body alive.

• It accounts for approximately 60-70% of total energy needs.

• BMR includes energy for heartbeat, respiration, and body temperature maintenance, but excludes digestion and voluntary activities.

• BMR varies among individuals.

Factors Affecting BMR

• Factors that Increase BMR:

  • Higher lean body mass

  • Greater height (more surface area)

  • Younger age

  • Elevated thyroid hormone levels

  • Stress, illness, and fever

  • Male gender

  • Pregnancy and lactation

• Factors that Decrease BMR:

  • Lower lean body mass

  • Lower height

  • Older age (decreases 3-5% per decade after age 30)

  • Depressed thyroid hormone levels

  • Starvation, fasting, or very low-calorie diets

  • Female gender (due to decreased lean tissue)

Physical Activity

• Physical activity increases energy expenditure beyond BMR.

• It varies widely among individuals based on type, duration, and intensity of activity.

• Non-Exercise Activity Thermogenesis (NEAT): Energy burned through movement outside of planned exercise (e.g., getting dressed, walking, fidgeting).

Thermic Effect of Food

• Thermic effect of food is the energy used to digest, absorb, transport, metabolize, and store nutrients.

• Fat requires very little energy to digest, transport, and store.

• Protein and carbohydrates require more energy to process.

• Processed foods require less energy to digest.

Healthy Body Weight

• A healthful weight:

  • Is maintained without constant dieting.

  • Is compatible with normal blood pressure, lipid levels, and glucose tolerance.

  • Considers family history of body shape and weight.

  • Promotes good eating habits and regular physical activity.

  • Is acceptable to the individual.

  • Considers weight history.

Evaluating Body Weight

• A person’s actual weight is not the only factor to consider.

• Evaluation should include:

  • Body Mass Index (BMI)

  • Measuring body composition

  • Assessing fat distribution pattern

Body Mass Index (BMI)

• BMI expresses the ratio of a person’s weight to the square of their height.

• BMI = \frac{Weight (kg)}{Height (m)^2}

• BMI values below 18.5 or above 30 indicate increased health risks.

• BMI is inexpensive, noninvasive, and easy to obtain, but it does not consider body composition.

• Adult BMI should not be applied to children, adolescents, older adults, pregnant or breastfeeding women, and individuals with higher lean body mass.

• BMI Categories:

  • Underweight: BMI < 18.5

  • Healthy weight: BMI 18.5 to <25

  • Overweight: BMI 25 to <30

  • Obese: BMI ≥ 30

Body Composition

• Obesity is defined as excessive body fat: >35% for women and >25% for men.

• Increased body fat is associated with increased health risks.

• Body composition measures body fat and lean body mass.

• Methods of measuring body composition:

  • Underwater weighing: Considered the most accurate (2-3% margin of error), but requires specialized equipment and trained technicians.

  • Skinfold measurements: Involves pinching skin folds at various locations (3-4% error if done by a skilled technician).

  • Bioelectrical Impedance Analysis (BIA): Sends a low electrical current through the body (3-4% error under best circumstances).

  • Dual-energy X-ray Absorptiometry (DXA): Uses low-level X-rays to differentiate between bone, lean tissue, and fat (2-4% error).

  • Bod Pod: Uses air displacement to measure body composition; promising but may overestimate body fat in some populations.

Body Fat Distribution

• Apple Shape (Upper Body Fat): Associated with increased risk of type 2 diabetes, heart disease, and hypertension.

• Pear Shape (Lower Body Fat): Associated with less risk of chronic disease.

• Waist Circumference Measurement:

  • >40” for men indicates increased risk

  • >35” for women indicates increased risk

• Types of Fat:

  • Subcutaneous fat: Stored directly under the skin; less health risks.

  • Visceral fat: Stored in the abdominal cavity; high amounts increase risk of chronic diseases.

• Excess visceral fat releases adipokines, which promote an inflammatory state increasing risk for heart disease, type 2 diabetes, stroke, metabolic syndrome, frailty and Alzheimer's disease.

Factors Affecting Body Weight and Composition

• Biology: Genetic predisposition, resting metabolic rate, appetite-regulating hormones.

• Physical Activity Environment: Cost, perceived safety.

• Individual Psychology: Stress, parental control over children’s diet.

• Societal Influences: Level of education, screen time.

• Food Environment: Advertisements.

• Food Consumption: Portion size, energy density.

• Neighborhood Design: Access to healthy and affordable food, safe access to physical activity.

• Sleep: Lack of sleep alters hormones that regulate hunger. Increases Ghrelin (hormone that increases food intake) and decreases Leptin (hormone that influences long-term regulation of fat mass).

Health Risks Associated with Obesity

• Hypertension

• Type 2 Diabetes

• Cardiovascular Disease

• Stroke

• Osteoarthritis

• Gallbladder disease

• Sleep apnea

• Certain cancers

• Infertility

• Gestational diabetes

• Liver disease