The Body Mass Index (BMI) is a numerical value derived from a person's weight and height, used to categorize individuals into weight ranges. It is calculated using the formula: weight in kilograms divided by height in meters squared. Obesity is a health condition characterized by excessive accumulation of adipose tissue that poses health risks, often diagnosed with a BMI ≥ 30. This excess fat storage occurs when surplus dietary calories are converted into triglycerides and stored in adipocytes (fat cells). Initially, adipocytes expand in size, but once they reach their capacity, they multiply, particularly in cases of extreme obesity.

A key enzyme, endothelial lipoprotein lipase, regulates fat storage by facilitating the transfer of triglycerides from the bloodstream into fat cells. This enzyme is more active in abdominal fat than hip fat, making abdominal fat accumulation a greater risk factor for elevated cholesterol levels and cardiovascular diseases. Obesity is also associated with chronic low-grade systemic inflammation, which contributes to insulin resistance and the development of type 2 diabetes mellitus.

The causes of obesity are complex and often multifactorial, with many remaining unidentified. Contributing factors include overeating during childhood, enhanced fat storage efficiency, and genetic predisposition. While overeating and sedentary lifestyles contribute to weight gain, some individuals with obesity may not consume more calories but have metabolic traits that promote fat accumulation. For example, in some instances, adipocytes may exhibit heightened lipoprotein lipase activity, altered receptor expression favoring fat storage, and release of inflammatory cytokines, exacerbating insulin resistance.