Obesity and its Causes

Physiology of Obesity

• Obesity is a complex, multifactorial condition involving genetic, environmental, and social factors
• Appetite and satiety are regulated by multiple humoral and neurological mechanisms, integrated in the hypothalamus
• Hormones involved in energy balance and appetite regulation include leptin, insulin, ghrelin, and peptide YY3-36

Causes of Obesity

• Genetic predisposition
• Disruption in energy balance
• Environmental and social factors

Models of Obesity Pathology

• Overeating and inactivity are simplistic views of obesity
• Various pathways lead to obesity, with complex interactions between factors

The Hypothalamic-Leptin Axis

• Leptin is produced in fat cells and triggers receptors in the hypothalamus
• This activates the "Spend Energy" mode, reducing appetite and increasing energy expenditure
• In the "Conserve Energy" mode, appetite increases, and metabolic rate decreases

Leptin Resistance

• Leptin receptors can be blocked, tricking the hypothalamus into thinking there is no leptin
• This leads to increased appetite, slowed metabolic rate, and increased fat storage
• Orexin-A stimulates hunger and wakefulness, contributing to obesity

Obesity Types

• Apple (android) type: central obesity, associated with higher morbidity risk
• Pear (gynoid) type: peripheral fat distribution, fewer health risks

Body Mass Index (BMI)

• Calculated by weight (kg) / height (m)² or weight (lbs) x 705 / height (in)²

Waist to Hip Circumferences

• Android: central fat distribution, increased waist circumference and WHR, associated with higher morbidity risk
• Gynaecoid: peripheral fat distribution, fewer health risks

Visceral Obesity and the Insulin Resistance Syndrome

• Characterized by central obesity, glucose intolerance, hypertension, atherosclerosis, and polycystic ovary syndrome

Measurement of Body Fat

• Skin fold thickness (skin pinch) measures subcutaneous fat
• Bioelectrical impedance analysis (BIA) estimates body composition

The Insulin Resistance Syndrome

• Clinical manifestations include central obesity, glucose intolerance, hypertension, atherosclerosis, and polycystic ovary syndrome
• Biochemical abnormalities include hyperinsulinemia, high TG, low HDL-C, and small, dense LDL particles

This quiz explores the concept of obesity, its physiology, and the various factors that contribute to it, including genetic predisposition and environmental factors.