Glucose is required by all your cells in your body to make energy so they can function. When you have too much glucose in your bloodstream, your cells convert this to glycogen (short-term store of glucose in the liver or muscles) or fat (long-term energy store in the fat cells).
Your blood sugar level balance is the key to maintaining steady energy levels, weight, and will also affect your appetite. Uneven blood glucose levels which peak and trough can cause many symptoms such as fatigue and weight gain. Eating sugary or starchy foods lacking in fibre will cause this.