Obesity

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).

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

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 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 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 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.

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

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

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.

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).