There is no human being alive on this planet with the natural setpoint of 260lb while 5'7" tall.
There are people with genetic predisposition for obesity, but they are far and few between.
The primary reason for majority of people to be obese is the lack of volue to calories balance in the aritificialy processed and enhanced food we eat.
A meal used to have a lot less calories than it has now - and be bigger as well. That caused us to be able to eat a lot, have it digested over a long period of time and the nutrients being released to the bloodstream constantly for a prolonged period without spikes and rushes.
If go off the "corporate lunch diet" - during Christmass for example and eat home cooked food only - I can eat up to 5 times as much as I do during a workweek - AND LOOSE WIEGHT. Obviously a large portion of fish and veggies will have the same or less calories than a the fast-burger with fries and cola AND they are released over a period of several hours - so you are not hungry so soon. The problem is that cooking a real meal from scratch without using ANY pre-processed components is a time consuming activity and very hard to do I there is nobody at home to do it outside the holidays.