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 and amino acids to enter cells in the body, particularly muscle and liver cells. Here, insulin and other hormones direct whether these nutrients will be burned for energy or stored for future use. (The brain and nervous system are not dependent on insulin; they regulate their glucose needs through other mechanisms.)
- 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 disease process is more severe than with type 2, and onset usually begins in childhood:
- Beta cells in the pancreas that produce insulin are gradually destroyed. Eventually insulin deficiency is absolute.
- Without insulin to move glucose into cells, blood glucose levels become excessively high, a condition known as hyperglycemia.
- Because the body cannot utilize the sugar, it spills over into the urine and is lost.
- Weakness, weight loss, and excessive hunger and thirst are among the consequences of this "starvation in the midst of plenty."
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 up to 95% of all diabetes cases. About 20 million Americans have type 2 diabetes, and half are unaware they have it. The disease mechanisms in type 2 diabetes are not wholly known, but some experts suggest that the disease may involve the following three stages in most patients:
- The first stage in type 2 diabetes is the condition called insulin resistance. Although insulin can attach normally to receptors on liver and muscle cells, certain mechanisms prevent insulin from moving glucose (blood sugar) into these cells where it can be used. Most patients with type 2 diabetes produce variable, even normal or high, amounts of insulin, and in the beginning this amount is usually sufficient to overcome such resistance. 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.
- Over time, the pancreas becomes unable to produce enough insulin to overcome 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). This effect is now believed to be particularly damaging to the body.
- Eventually, the cycle of elevated glucose further impairs and possibly destroys beta cells, thereby stopping insulin production completely and causing full-blown diabetes. This is made evident by fasting hyperglycemia, in which elevated glucose levels are present most of the time.
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. Studies indicate that when people with type 2 diabetes maintain intensive exercise and diet modification programs, many 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.]
