First it is important to supply our body with essential land valuable nutrients, and to have a good balance of all the nutrients for our system to function properly.
White sugar is an unnatural molecule completely devoid of any nutritional value. At the same time it has concentrated energy and is often referred to as "empty calories". Overtime ingestion of large amounts will result in the person having sufficient energy to fuel the body but will lack in other essential nutrients.
In addition to white sugar, most people consume sucrose as you will find this is white bread, cereal, pasta, and other food made with white floor and all contains lots of sucrose.
The human body tries to cope with such an enormous consumption of sugar by increasing its insulin production. The continuous overeating of sugar inevitably lead to the condition know as "hypoglycemia" which is dangerous for the brain.
Our body cannot function without sugars at all though so it is important to provide the best sugar for our body. It is best to get your sugar from fruits and honey, it will provide you with energy and valuable nutrients.
I would require a much longer answer to explain everything... hope this helps!