What Is Obesity—And What It Is Not

Obesity vs Overweight: Understanding the Difference

Many people use the terms "obesity" and "overweight" interchangeably, but medically, they represent different levels of excess body weight. The most commonly used tool to categorize weight status is Body Mass Index (BMI), calculated as weight in kilograms divided by height in meters squared.

International BMI Classifications

The World Health Organization (WHO) defines the following categories for adults:

• Underweight: BMI less than 18.5
• Normal weight: BMI 18.5 to 24.9
• Overweight: BMI 25.0 to 29.9
• Obesity Class I: BMI 30.0 to 34.9
• Obesity Class II: BMI 35.0 to 39.9
• Obesity Class III (Severe): BMI ≥ 40

Indian-Specific BMI Cut-offs

Indians and other South Asians develop obesity-related health problems at lower BMI levels than Caucasian populations. This led to revised BMI cut-offs for Asian populations:

Fat Is Not Just "Extra Weight"

Many people think of body fat as simply stored energy—extra calories sitting passively in the body. This understanding is outdated and incorrect.

Adipose Tissue as an Endocrine Organ

Modern science recognizes adipose tissue (body fat) as an active endocrine organ that secretes over 600 different substances called adipokines. These include:

• Leptin: Regulates appetite and energy expenditure
• Adiponectin: Improves insulin sensitivity (decreased in obesity)
• Resistin: Promotes insulin resistance
• Inflammatory cytokines: TNF-α, IL-6, promoting chronic inflammation
• Plasminogen activator inhibitor-1 (PAI-1): Increases blood clotting risk

Visceral Fat: The Dangerous Type

Not all fat is created equal. Body fat exists in two main compartments:

1. Subcutaneous fat: Located under the skin, relatively metabolically inert
2. Visceral fat: Stored around internal organs in the abdominal cavity

Visceral fat is metabolically active and dangerous. It releases inflammatory molecules directly into the portal vein leading to the liver, causing insulin resistance, fatty liver disease, and metabolic dysfunction. Indians tend to accumulate more visceral fat relative to subcutaneous fat—even at normal or low BMI.

Why Obesity Is a Disease, Not a Lack of Willpower

One of the most harmful misconceptions about obesity is that it results from laziness, gluttony, or lack of self-control. This belief causes tremendous psychological harm and prevents people from seeking medical help.

Obesity as a Chronic Disease: WHO Recognition

In 2013, the American Medical Association (AMA) officially recognized obesity as a chronic disease. The World Health Organization (WHO) and medical organizations worldwide have followed suit. This classification is based on:

• Complex etiology: Genetic, metabolic, environmental, psychological factors
• Chronic nature: Requires long-term management, not quick fixes
• Multiple complications: Leads to diabetes, heart disease, cancer, etc.
• Physiological mechanisms: Hormonal dysregulation, metabolic adaptation

Metabolic Adaptation: Why "Eat Less, Move More" Fails

When people with obesity lose weight, their body doesn't respond the same way as someone who was never obese:

• Metabolic rate drops beyond what's expected from weight loss alone
• Hunger hormones increase: Ghrelin (hunger hormone) rises, leptin (satiety hormone) falls
• Energy efficiency improves: The body burns fewer calories for the same activities
• Fat storage becomes more efficient: The body aggressively tries to regain lost weight

This phenomenon, called metabolic adaptation or "adaptive thermogenesis," has been documented in numerous studies. It explains why over 95% of people who lose weight through diet and exercise alone regain it within 5 years—not due to lack of willpower, but due to biological resistance.

Neurological Components

Brain imaging studies show that people with obesity have altered activity in regions controlling:

• Reward processing: Enhanced response to food cues
• Impulse control: Reduced activity in prefrontal cortex
• Satiety signaling: Leptin resistance at the hypothalamic level

These are neurobiological differences, not character flaws.

Key Takeaways