The Bottom Line Eating too much added sugar can have many negative health effects. An excess of sweetened foods and beverages can lead to weight gain, blood sugar problems and an increased risk of heart disease, among other dangerous conditions. Why sugar is bad for your brain?
Although the brain needs glucose, too much of this energy source can be a bad thing. … The effects of glucose and other forms of sugar on the brain may be the most profound in diabetes, a group of diseases in which high blood glucose levels persist over a prolonged period of time.

How sugar affects the brain Ted?
When you eat something loaded with sugar, your taste buds, your gut and your brain all take notice. This activation of your reward system is not unlike how bodies process addictive substances such as alcohol or nicotine — an overload of sugar spikes dopamine levels and leaves you craving more.