Obesity is the excessive accumulation of weight that exceeds the body's skeletal and physical standards. The American Society for Metabolic and Bariatric Surgery (ASMBS) defines obesity as "a lifelong progressive, life-threatening, costly, genetically related, multi-factorial disease of excess adipose tissue storage." It's the No. 2 cause of preventable death in the United States.
People are considered obese if their body mass index (BMI) is 30 or higher. Although it has a simple definition, obesity is a very complex health condition that's caused by a combination of many factors. It occurs as a result of food and physical behaviors, but it's also influenced by environmental, economic, societal and genetic factors.
Science also shows that our bodies undergo genetic changes in response to our environment. Stress and lack of sleep impact our hormones, which influence hunger response, adipose tissue storage and ultimately, our weight.