Assuming that everyone considers allowing children to starve is immoral are the obese immoral AND that obese person doesn't suffer from weight-gain medical conditions?
From my perspective it's a sign of gluttony. Poor nutrition is the cause of death in almost 50 percent of children under five world wide, some 805 million people do not have enough food to lead an active healthy life. So how then can some people ethically overeat to the point of obesity.