Depression, anorexia are examples about how finally it is a battle between higher cognitive signals and the biological drive. These are exceptions (deviating the norm) where the stimulus is so strong that it could override the basic drive. And we have animal studies which clearly shows a biological basis of obesity. They aren't really affected by social, cultural, economic and problems like anorexia. A genetic predisposition doesn't mean that it is physically impossible. If they eat less and work more, they will lose. But it is extremely hard. It would like me telling you to cut down to 5% body fat and just stay like that for the rest of the life. Sure it is possible, but pretty much guaranteed that you will never maintain. The same for most obese. And in research is pretty clear that we are failing. Almost 80-90% of the people gain most of it back in 3-5years. There are single gene mutations (5-10% -severely obese people) and complex interactions of a lot of genes that determine your obesity. It is just like height. It is not that the very tall people and very short people's height is due to genetics. Everyone's height is majorly determined by their genes. Or I should say 90% of the variation in height is from genes. Obesity is just second to height for genetic contribution.