Dopamine!

The more we have sugar, the greater the amount of dopamine released in our brain. Dopamine is responsible for positive emotions, and once triggered by something, the human body wants it more. So if a person likes sugar, his brain releases dopamine which causes him to feel good. Hence, the person craves more sugar.

There are a number of strands you could consider when you answer this question, and so narrowing down what you want to focus on will help you to plan.

The brain needs sugar to function, so one of the most basic answers is that we have evolved to crave sugar in order to keep our brains functioning at full capacity. In our evolutionary past, sugar would not always have been easy to come across, so... more