Glucose (a type of sugar) is the body's main energy source. But when the body can't use glucose for energy, it uses fat instead. When fat is broken down, chemicals called ketones are produced. They get into a person's blood and urine (pee). High levels of ketones cause the blood to become more acidic. This can occur when not enough food has been eaten to provide glucose for energy, or it can occur in diabetes, when the body can't use glucose normally.