If that is so, perhaps you could tell me why it is that an examination of hundreds of thousands of photos taken from the dawn of photography to the present age show that the Americans of the past--middle-class or upper-class Americans who did not have to do hard physical labor--were not fat? If heredity helped to determine weight, then our ancestors should have been obese as we are today. Perhaps also you could explain why it is that, while modern Americans are obese, their near cousins in Europe or Africa or Asia are not fat, even when there is an abundance of food back in the old country.
Mind, I'm not saying there may not be a biological basis to obesity. Behavior can actually change brain wiring. I'm saying there is no good evidence that obesity is genetically linked. Probably only identical twin studies could begin to establish that.