Class 1 obesity is a type of obesity that is diagnosed when a person has a BMI (body mass index) between 30 and less than 35. BMI is a measure of body fat based on a persons height and weight. Class 1 obesity is also sometimes referred to as "low-risk" obesity. Obesity is a serious, chronic disease that can lead to other health problems, including diabetes, heart disease, and some cancers. The different classes of obesity indicate the severity of obesity, with class 3 being the most severe. Depending on the severity of obesity, different treatment options may be available.