Introduction
The two major forms of diabetes are type 1, previously called insulin-dependent diabetes mellitus (IDDM) or juvenile-onset diabetes, and type 2, previously called non-insulin-dependent diabetes mellitus (NIDDM) or maturity-onset diabetes. [For more information, see In-Depth Report #9: Diabetes - type 1 and In-Depth Report #60: Diabetes - type 2.]
Insulin
Both type 1 and type 2 diabetes share one central feature: elevated blood sugar (glucose) levels due to absolute or relative insufficiencies of insulin, a hormone produced by the pancreas. Insulin is a key regulator of the body's metabolism. It normally works in the following way:
- During and immediately after a meal, digestion breaks carbohydrates down into sugar molecules (of which glucose is one) and proteins into amino acids.
- Right after the meal, glucose and amino acids are absorbed directly into the bloodstream, and blood glucose levels rise sharply. (Glucose levels after a meal are called postprandial levels.)
- The rise in blood glucose levels signals important cells in the pancreas, called beta cells, to secrete insulin, which pours into the bloodstream. Within 10 minutes after a meal insulin rises to its peak level.
- Insulin then enables glucose to enter cells in the body, particularly muscle and liver cells. Here, insulin and other hormones direct whether glucose will be burned for energy or stored for future use.
- When insulin levels are high, the liver stops producing glucose and stores it in other forms until the body needs it again.
- As blood glucose levels reach their peak, the pancreas reduces the production of insulin.
- About 2 - 4 hours after a meal both blood glucose and insulin are at low levels, with insulin being slightly higher. The blood glucose levels are then referred to as fasting blood glucose concentrations.
Type 1 Diabetes
In type 1 diabetes, the pancreas does not produce insulin. Onset is usually in childhood or adolescence. Type 1 diabetes is considered an autoimmune disorder.
Patients with type 1 diabetes need to take insulin. Dietary control in type 1 diabetes is very important and focuses on balancing food intake with insulin intake and energy expenditure from physical exertion. [For more information, see In-Depth Report #9: Diabetes - type 1.]
Type 2 Diabetes
Type 2 diabetes is the most common form of diabetes, accounting for 90 - 95% of cases. In type 2 diabetes, the body does not respond properly to insulin, a condition known as insulin resistance. In type 2 diabetes, the initial effect of this stage is usually an abnormal rise in blood sugar right after a meal (called postprandial hyperglycemia).
Patients whose blood glucose levels are higher than normal, but not yet high enough to be classified as diabetes, are considered to have pre-diabetes.It is very important that people with pre-diabetes control their weight to stop or delay the progression to diabetes.
Obesity is common in patients with type 2 diabetes, and this condition appears to be related to insulin resistance. The primary dietary goal for overweight type 2 patients is weight loss and maintenance. With regular exercise and diet modification programs, many people with type 2 diabetes can minimize or even avoid medications. Weight loss medications or bariatric surgery may be appropriate for some patients. [For more information, see In-Depth Report #60: Diabetes - type 2 and In-Depth Report #53: Weight control and diet.]
