Obesity develops when energy intake consistently exceeds energy expenditure.

When caloric intake is greater than energy expenditure, excess calories are stored as body fat. Therefore, obesity is fundamentally the result of a chronic imbalance between caloric intake and caloric expenditure. Conversely, when energy intake is lower than energy expenditure, weight loss occurs regardless of the presence of risk factors or underlying diseases. In this context, the law of conservation of energy always applies. Nevertheless, the development of obesity is promoted by a variety of genetic, environmental, behavioral, and medical risk factors.

Overview: Risk Factors for Obesity

• Family predisposition and genetic factors
  • Children who are large for gestational age (LGA) have approximately a 1.5-fold higher risk of developing obesity during adolescence (43.7% prevalence).
  • Adolescents with normal body weight almost invariably had normal weight throughout childhood.
  • Approximately 50% of overweight adolescents were already overweight by the age of five years, with excess weight increasing progressively throughout childhood.
  • Ninety percent of children with obesity at three years of age remain obese during adolescence.
  • The greatest acceleration in weight gain occurs between the second and sixth years of life.
• Lifestyle factors
  • Physical inactivity
  • Unhealthy dietary habits
• Continuous availability of food
• Sleep deprivation
• Chronic psychological stress
• Depressive disorders
• Low socioeconomic status
• Eating disorders
  • e.g., Binge Eating Disorder (BED)
  • Night Eating Syndrome (NES)
• Endocrine disorders
  • e.g., hypothyroidism
  • Cushing syndrome
• Medications
  • Antidepressants
  • Antipsychotics (neuroleptics)
  • Mood stabilizers
  • Antiepileptic drugs
  • Antidiabetic medications
  • Glucocorticoids
  • Certain hormonal contraceptives
  • Beta-blockers
• Other contributing factors
  • Prolonged immobilization
  • Pregnancy
  • Smoking cessation