Live Science has an article which says that scientists can predict your shape simply by looking at your genes.
From that you would suppose there is no use in exercising, in eating right, in staying healthy.
But I’m going to ignore those findings and say that being overweight, while partially a function of genetics, can be regulated by exercising, eating right, and staying healthy. (Illness that cause obesity such as Cushing’s are excluded. Obviously if you can’t get healthy, you can’t stay healthy.)
Not everyone throughout the history of the US has been overweight. In fact, obesity is a relatively new phenomenon in the US. So unless we’ve all caught a virus that makes us overweight, which is apparently possible, it must be related to the way we’re living now as opposed to one hundred, even thirty, years ago.