There are many ways to become morbidly obese including consuming too many calories (and not burning those calories off with exercise). Other factors (stress, medication, pregnancy and other hormone changes, aging, etc.) that can cause someone to be at a greater risk of becoming obese. Additionally, there is a genetic component to obesity. There isn’t yet a clearcut gene identified, but obesity runs in families (or even countries) where large populations of people and families are all morbidly obese.