Obesity Overview and BMI Classification

Obesity Overview

• Obesity is having excessive body fat.
• It differs from overweight, which is simply weighing too much, possibly due to muscle, bone, or water content.
• Both conditions mean a person's weight exceeds a healthy level for their height.

Body Mass Index (BMI)

• Obesity is defined by a BMI greater than 30 kg/m2.
• Overweight is defined as a BMI between 25 and 30 kg/m2.
• BMI is calculated by dividing weight in kilograms by height in meters squared.
• BMI is a screening tool for overweight and obesity.

Adult BMI Ranges

• Underweight: BMI less than 18.5
• Normal: BMI 18.5 to <25
• Overweight: BMI 25.0 to <30
• Obese: BMI 30 or higher
• Class 1 obesity: BMI 30–35
• Class 2 obesity: BMI 35–40
• Class 3 obesity (severe/extreme): BMI 40 or higher

Energy Imbalance

• Obesity often results from an energy imbalance, where energy intake exceeds energy expenditure.
• Energy in: calories consumed from food and drinks.
• Energy out: calories used for bodily functions (breathing, digestion, activity, body temp).

Body Fat Storage

• Carbohydrates (sugars) are stored as glycogen in the liver and muscles.
• Fats are stored as triglycerides in fat tissue.
• The amount of energy the body gains from food depends on food type, preparation methods and time since last meal.

Types of Fat Tissue

• White fat: Stores energy, influences appetite control, hormon production and inflammation.
• Brown fat: Releases energy as heat, particularly important in infants.
• Beige fat: Has characteristics of both white and brown fat, produces heat.

Complications of Obesity

• Cosmetic problems.
• Roughly 112,000 deaths in the US per year directly related to obesity, in patients with BMI over 30. Life expectancy is significantly reduced for those with a BMI over 40.
• Increased risk of chronic diseases:
  • Insulin resistance
  • Type 2 diabetes
  • Coronary artery disease
  • Cancer
  • Hypertension
  • High cholesterol
  • Stroke
  • Congestive heart failure
  • Gallstones
  • Gout and gouty arthritis
  • Osteoarthritis
  • Sleep apnea

Causes of Obesity

• Genetics: Potential impact on body fat storage, fat distribution, energy conversion and exercise efficiency. Leptin deficiency is one such example.
• Overeating: consuming more calories than body burns. High energy density foods (fast food, fried food, sweets) play a significant role.
• Diet high in simple carbohydrates: Rapid absorption and consequent pronounced insulin release contributes to weight gain as opposed to complex carbohydrates.
• Eating frequency: Frequent small meals can aid with cholesterol and blood sugar regulation, while large meals result in large spikes in insulin after meals.
• Physical inactivity: Fewer calories burned by sedentary individuals leading to weight gain.
• Medications: Certain antidepressants, anticonvulsants, diabetes, hormones and some blood pressure/antihistamine medications can contribute to weight gain.
• Psychological factors: Emotions like boredom, sadness, stress, or anger can cause overeating.
• Endocrine disorders (e.g., hypothyroidism, Cushing's syndrome): Hormonal imbalances can impact metabolism and energy regulation, leading to weight gain.
• Hormones: Women tend to gain weight during events like pregnancy, menopause, oral contraceptive use (though this risk has mitigated with lower dose estrogens).

Fat Distribution

• Body shape and regional fat distribution are often more important for health than total body fat.
• Visceral fat (fat around internal organs) is problematic, compared to subcutaneous fat located under the abdomen skin).
• Central obesity (excess abdominal fat) is linked to various health issues.
• Android (upper body fat) and gynoid (lower body fat) patterns differ in cellular characteristics due to testosterone/estrogen influence, also influencing fat cell receptor types and distribution throughout the body.

Explore the essential concepts of obesity and Body Mass Index (BMI) in this informative quiz. Learn about the different classifications of obesity and their implications on health. Understand the relationship between energy imbalance and obesity.