“Diabetes” actually refers to a group of diseases called “diabetes mellitus.” These diseases affect how the body processes glucose (blood sugar). Glucose is an essential source of energy for the cells that make up tissues and muscles. Glucose is also the brain’s primary source of fuel. Chronic diabetes conditions include type 1 diabetes and type 2 diabetes. Some forms of diabetes are reversible. These include prediabetes, in which blood sugar levels are higher than normal but not in need of treatment, and gestational diabetes, which occurs during pregnancy but is generally resolved after delivery. All types of diabetes are caused by an overabundance of glucose and may lead to serious health problems.