Obesity is more than just being overweight. People are considered to be obese if they have a body mass index (BMI) of 30 or greater. (Those who are overweight have a BMI of 25 to 29.9) Obesity increases the risk of diabetes, heart disease, high blood pressure, stroke, some types of cancer, and even dementia later in life. Despite the health risks, it can be very difficult to shed extra pounds, and keep them off.