why we like unhealthy food.

http://www.livescience.com/history/080208-hn-sugar.html

Many of us humans die of obesity caused heart disease every year. Mainly because our bodies prefer unhealthy food. But why?
When we were cavemen, the swet fruits were more nutritious, so we generally preffered the sweet taste. The brain also need glucose to function. Unfortunantly, this later led to us growing sugar cane and developing type 2 diabetes to satisfy our sweet teeth.