Obesity is a medical condition involving excessive body fat that causes health problems. Body mass index (BMI) is used to measure obesity, calculated from a person's weight and height, with different BMI ranges indicating underweight, normal weight, overweight, and classes of obesity. Obesity can lead to disorders like diabetes, heart disease, hypertension, cancer, gout, sleep apnea, kidney disease, and gallbladder disease. Maintaining a healthy lifestyle through diet, exercise, avoiding smoking and excess alcohol can help prevent and manage obesity and related disorders.