Why glucose cant be stored in human body?

Glucose can't be stored in the human body because it is a carbohydrate.  Carbohydrates have to be converted to another form before they can be used as fuel for the body.  The cellular respiration equation uses glucose, combined with oxygen to produce energy in the form of ATP (adenosine triphosphate), along with carbon dioxide and water vapor as waste products.  As is the case with most things in nature, excessive ATP is stored in the liver until needed.  If the body continues to have excessive ATP, at some point it is converted into fat cells, which is the body's way of saving excess energy.  Fat is in the form of lipids and has twice the calorie count of carbohydrates.  One gram of fat has 9 calories, while 1 gram of carbohydrates has 4 calories.