In medicine terms, blood sugar means the amount of glucose present in the blood. Glucose is the primary form of energy in the cells of the body. Glucose levels rise after a meal and remain at a low in the morning. Though it is called "blood sugar", there are other forms of sugar in our blood as well such as fructose and galactose. Glucose should neither be high nor too low. If it remains high, there is a possibility of causing long term health problems such as diabetes and if the glucose level remains too low, one can suffer from lethargy. Milk increases blood sugar in the body. It is recommended to drink skim milk than whole milk, as skim milk has low levels of unsaturated fat.