Obesity is defined as excess body fat that negatively impacts health and reduces life expectancy. Body mass index (BMI) is a common measurement used to determine if a person's weight is healthy, normal, overweight, or obese. People with a BMI over 30 are considered obese. Obesity increases the risk of health conditions like heart disease, diabetes, and certain cancers. It is usually caused by eating more calories than burned through physical activity and can be genetic. Reducing obesity involves diet, exercise, and lifestyle changes.