As humans we have a very interesting relationship with food. We have an intense need to always eat more.
Biologically we are just trying to survive. Our DNA believes we live in a world of scarcity and starvation, thus forces us to binge as much as possible then our fat cells store as much energy as they can.
The result is that we are all fat.
I guess we would need to re-engineer human DNA to put a stop to obesity.