What is Obesity » obesity is a medical condition when excess body fat has accumulated to a level that it may affect your health negatively. Obesity could cause a reduced life expectancy and increased health problems. Using Body mass index (BMI), a measurement that compares weight and height, people are considered at moderate risk if their BMI is between 25 kg/m² and 30 kg/m², and at high risk when it is greater than 30 kg/m². Find out more »