Back in the past (very long ago!), you could find genetic makeup which was favourable towards energy storage in the body. So when the food was available it would be eaten and stored efficiently, and when the winter came making surroundings less conducive to grow and find food, we had to rely on our energy stores for the snowy day.
There were also people who did not develop such mechanisms and had to survive by constantly looking for food, actively more when food was scarce in the winter. So their genetic makeup was sort of unfavourable for the time being.
Today with greater and cheaper availability of food throughout the year things have changed. The people who inherited the high tendency to store energy in the body seem more likely to become obese. The favourable mechanism of the past became unfavourable in the present.
As for people who did not have this mechanism in the first place, and were disadvantaged earlier now live in the conditions that is favourable to them. That is they can eat as much as they want and don’t seem to get fat since they don’t have the tendency to store the food they eat.
This tells us no matter the genetic makeup we’re born with, the environment has the capacity to sway in the game in your favour.
It is difficult to change one’s genes but not as tough as it is to change the environment. It’s like mountain and river. Mountain is your gene and river is your environment. It is difficult to move the mountain (almost impossible) on our own, but it is relatively easier to change the course of the river. Not to say that it is easiest of all the tasks in the world but at least it is not close to impossible. Making environmental changes will tire you out but the end result will be that you will have major control over your lifestyle.