To be very short,
1. Sugar will activate the reward system in your brain.
2. Dopamine will kill you to keep hunting for more sugar as reward.
3. Sugar is actually not reward but threat! Your body cannot produce Insulin enough to deal with too much sugar. – Diabetes.
4. Dopamine is the chemical that plays very important roles for your greed, so beware of it. (Spiritually, M I N D! )