Diabetes mellitus may be categorised into several types but the two major types are type 1 (insulin-dependent diabetes mellitus; IDDM) and type 2 (non-insulin-dependent diabetes mellitus; NIDDM). The term juvenile-onset diabetes has sometimes been used for type 1 and maturity-onset diabetes for type 2. Malnutrition-related diabetes is no longer considered a separate entity (see Effects of Cassava, under Adverse Effects of Starch.
Type 1 diabetes mellitus is present in patients who have little or no endogenous insulin secretory capacity and who therefore require exogenous insulin therapy for survival. This form of the disease has an auto-immune basis in most cases, and usually develops before adulthood. The associated hypoinsulinaemia and hyperglucagonaemia put such patients at risk of ketosis and ketoacidosis.
In type 2 diabetes mellitus the disease typically develops in later life. Insulin secretion may appear normal or even excessive (and type 2 patients are thus less prone to ketosis) but it is insufficient to compensate for insulin resistance. Obesity is present in the majority of type 2 patients; non-obese patients tend to have low insulin secretory capacity (although not as low as in type 1 diabetes) rather than appreciable insulin resistance. It is closely associated with cardiovascular disease, and the 2 may arise from a common antecedent described as the metabolic syndrome.