A 2018 study suggested that three types should be abandoned as too simplistic. It classified diabetes into five subgroups, with what is typically described as type 1 and autoimmune late-onset diabetes categorized as one group, whereas type 2 encompasses four categories. This is hoped to improve diabetes treatment by tailoring it more specifically to the subgroups.
Metabolic syndrome is thought to be caused by adipose tissue dysfunction and insulin resistance. Dysfunctional adipose tissue also plays an important role in the pathogenesis of obesity-related insulin resistance.  Both adipose cell enlargement and infiltration of macrophages into adipose tissue result in the release of proinflammatory cytokines and promote insulin resistance. 
On physical examination, hypertension may be associated with the presence of changes in the optic fundus seen by ophthalmoscopy. The severity of the changes typical of hypertensive retinopathy is graded from I to IV; grades I and II may be difficult to differentiate. The severity of the retinopathy correlates roughly with the duration or the severity of the hypertension.
Cycle the diet in a way that has periods of reduced energy intake and periods of increased energy intake. This helps offset the leptin decline that occurs with dieting. There is individual variation with this, but for those who respond well, a day or a few days of overeating can set the metabolic rate back to a higher level. This cycling approach may be more effective for fat loss than the traditional approach
In autoimmune diseases, such as type 1 diabetes, the immune system mistakenly manufactures antibodies and inflammatory cells that are directed against and cause damage to patients' own body tissues. In persons with type 1 diabetes, the beta cells of the pancreas, which are responsible for insulin production, are attacked by the misdirected immune system. It is believed that the tendency to develop abnormal antibodies in type 1 diabetes is, in part, genetically inherited, though the details are not fully understood.
Along with the increased hunger and cravings comes the metabolic slow down. This is most impacted by the hormone leptin. Less insulin exposure to the fat cell and a shrinking fat cell means the metabolic hormone leptin is reduced. Low leptin means increased hunger. Low leptin also means decreased activity of the body’s two major metabolic engines, the thyroid and the adrenal glands. So as leptin decreases, your metabolism gets the signal to stop burning energy and to start consuming it.
^ Ostchega Y, Dillon CF, Hughes JP, Carroll M, Yoon S (July 2007). "Trends in hypertension prevalence, awareness, treatment, and control in older U.S. adults: data from the National Health and Nutrition Examination Survey 1988 to 2004". Journal of the American Geriatrics Society. 55 (7): 1056–65. doi:10.1111/j.1532-5415.2007.01215.x. PMID 17608879.
As evident from the above, younger individuals may present with hypertension associated with an elevated cardiac output (high-output hypertension). High-output hypertension results from volume and sodium retention by the kidney, leading to increased stroke volume and, often, with cardiac stimulation by adrenergic hyperactivity. Systemic vascular resistance is generally not increased at such earlier stages of hypertension. As hypertension is sustained, however, vascular adaptations including remodeling, vasoconstriction, and vascular rarefaction occur, leading to increased systemic vascular resistance. In this situation, cardiac output is generally normal or slightly reduced, and circulating blood volume is normal.
^ Qaseem A, Wilt TJ, Rich R, Humphrey LL, Frost J, Forciea MA (17 January 2017). "Pharmacologic Treatment of Hypertension in Adults Aged 60 Years or Older to Higher Versus Lower Blood Pressure Targets: A Clinical Practice Guideline From the American College of Physicians and the American Academy of Family Physicians". Annals of Internal Medicine. 166 (6): 430–437. doi:10.7326/M16-1785. PMID 28135725.
The Caerphilly Heart Disease Study followed 2,375 male subjects over 20 years and suggested the daily intake of a pint (~568 ml) of milk or equivalent dairy products more than halved the risk of metabolic syndrome. Some subsequent studies support the authors' findings, while others dispute them. A systematic review of four randomized controlled trials found that a paleolithic nutritional pattern improved three of five measurable components of the metabolic syndrome in participants with at least one of the components.
Insulin is vital to patients with type 1 diabetes - they cannot live without a source of exogenous insulin. Without insulin, patients with type 1 diabetes develop severely elevated blood sugar levels. This leads to increased urine glucose, which in turn leads to excessive loss of fluid and electrolytes in the urine. Lack of insulin also causes the inability to store fat and protein along with breakdown of existing fat and protein stores. This dysregulation, results in the process of ketosis and the release of ketones into the blood. Ketones turn the blood acidic, a condition called diabetic ketoacidosis (DKA). Symptoms of diabetic ketoacidosis include nausea, vomiting, and abdominal pain. Without prompt medical treatment, patients with diabetic ketoacidosis can rapidly go into shock, coma, and even death may result.