The scientific and social study of obesity has shown that it is a complex bodily disorder, the causes of which are multiple and varied, and may include genetic and epigenetic factors, diet and eating habits, socioeconomic status, and personal and social lifestyles.
Wtf?
Yes, there's a lot involved, but excusing away obesity as genetic ignores that 99% of it is behavioural. Just look at the explosion of Type II diabetes, which is pretty much all caused by diet.
Growing up, there were exactly 2 obese kids in our school, from first grade through 12th (across all grades). Those kids had a genetic cause to their obesity.
Today we have a much higher rate - I'm not buying that genetics drastically changed over the last few decades.
The elephant in the room is a combination of bullshit from governmental agencies (the lie of the food pyramid anyone?), nonsense from the medical community (fat in our diet isn't the driver of cardiovascular disease or obesity, it's unstable glucose, something that's been well known since the early 90's), pushing a high-carb diet in the 80's, which was a lie that ran counter to what doctors advised for diabetetics since the 1930's!