The discovery of the obesity gene in humans half a decade ago offered evidence that chronic weight gain is the consequence of  a mismatch between nature and nurture.   Simplistic explanations, such as blaming obesity on  a drop   in   fat  consumption,  ignore scientific reality. In  countries like India and China,   obesity  was virtually  unknown until  the introduction of a high-fat, Western-style diet.  

One  well-known reason for this is that dietary fat converts to body fat more effciently than does  protein   or carbohydrate,  but recently scientists have uncovered what appears to be  an equally important factor. Some researchers in  universities are investigating the possibility that high levels of fat and fructose are mucking up  our brain   chemistry , and thereby muting the signals that would normally tell us  to  put  down the  fork. These signals are produced by peptides, which are regulated by a number of hormones. Under normal conditions these hormones help maintain a stable body weight by adjusting levels of the peptides that control eating. But a diet loaded with fat and fructose hampers the regulation of these hormones. Complicating matters still further is that the brain loses its ability to respond to these hormones as body fat increases -- so the obese are doubly penalized.  

        Sarah   Leibowitz ,a neurobiologist, believes that frequent exposure  to fatty  foods may configure the brain to crave   still more fat.She has  shown in animal studies that galanin, a brain peptide that simulates eating behavior and decreases energy expenditure,increases when the  animal  eats a high-fat diet.  

        There are many factors contributing to the explosion of obesity in the United   States,  and  the world, but the      radical changes in the composition of our diet are first among them.While scientific work in this arena is in its infancy, it's already clear that varying  the amount  of fat  and other  nutrients  in   the diet affects brain chemistry by activating  certain genes, and this in turn directs our dietary preferences. By submitting  ourselves to a  steady  dose of  highly processed, sweet, high-fat foods, we  have unwittingly entered into a dangerous   experiment,  the long-term  consequences   of  which are only now beginning to surface.