Glucose is carried in your blood to cells throughout your body. Thus glucose is an important fuel for cells. If the amount of glucose in your blood were to drop too low your cells would be deprived of fuel. Most of your cells can use fat for energy but your brain and nervous system depend on glucose for fuel. To keep these cells fed your blood must maintain a constant supply of glucose.
The amount of glucose in the blood is regulated at about 60 to 100 mg per 100 ml of blood (70 to 120 mg/100 ml serum) by hormones from the pancreas. If these hormones don't work properly, glucose levels can rise too high—as occurs in diabetes. Although the symptoms of high blood sugar are not always felt right away, diabetes has serious long-term consequences.
Blood glucose levels rise after you eat
After you eat, the carbohydrate in your food is digested and absorbed and enters your bloodstream as glucose. How quickly and how high blood glucose rises after carbohydrate is consumed is referred to as glycemic response. The glycemic response of a specific food can be quantified by its glycemic index. The higher the glycemic index, the greater the rise in blood sugar after consuming that food. However, since we typically eat meals containing a variety of foods, knowing the glycemic index of a specific food does not tell us much about what blood glucose levels will be after eating a meal.
Glycemic response is affected by the amount and type of carbohydrate in a food or meal as well as its fat and protein content. Because carbohydrate must be digested and absorbed to enter the blood as glucose, how quickly a food leaves the stomach affects how quickly glucose gets into the blood. Carbohydrate consumed alone leaves the stomach quickly and causes a rapid rise in blood sugar. For example, when you drink a can of soda or eat some cotton candy, your blood sugar can increase within a matter of minutes. Some starches, such as potato starch, cause blood glucose to rise even more quickly than sugar. These foods have a high glycemic index. Fiber takes longer to leave the stomach and slows absorption in the small intestine so fiber-containing foods cause a slower increase in blood sugar. Fat and protein take longer to leave the stomach than carbohydrate, so when consumed with these nutrients, carbohydrate leaves the stomach and hence enters the blood more slowly. Therefore foods high in fiber, fat, and protein generally have a lower glycemic index than purer sources of sugar or starch. After a mixed meal, such as chicken, brown rice, and green beans, which contains carbohydrate, fat, protein, and fiber, it will take 30 to 60 minutes before blood glucose begins to rise.
Insulin lowers blood glucose
The rise in blood glucose that occurs after eating signals the pancreas to secrete insulin. Insulin is a hormone that allows glucose to be taken into the cells of the body. As glucose enters the cells, blood glucose levels drop to the normal pre-meal levels. Insulin also has other important functions. In the liver, it promotes the storage of glucose as glycogen and, to a lesser extent, fat. In muscle, insulin stimulates the uptake of glucose for energy production and the synthesis of muscle glycogen for energy storage. Insulin also stimulates protein synthesis, and in fat-storing cells it promotes the conversion of glucose to fat for storage.
Glucagon raises blood glucose
A few hours after eating, the glucose levels in the blood—and consequently glucose available to the cells—begins to decrease. This triggers the pancreas to secrete the hormone glucagon. Glucagon signals liver cells to break down glycogen into glucose, which is released into the bloodstream bringing glucose levels back to normal. Glucagon also stimulates the synthesis of new glucose molecules from 3-carbon molecules, most of which come from the breakdown of amino acids from body proteins.
Diabetes Occurs When Glucose Levels Stay Too High
Diabetes mellitus is characterized by consistently high levels of blood glucose due to either a lack of insulin or an unresponsiveness of body cells to insulin. Over 18 million people in the United States have diabetes; more than 5 million of these do not know that they have the disease. The incidence is higher among minority groups, particularly African Americans, Hispanic Americans, and Native Americans.
Blood glucose levels are used to diagnose diabetes. After an 8-hour fast, normal blood glucose is less than100 mg/100 ml. Prediabetes is defined as a fasting blood glucose between 100 and 125 mg/100 ml, and diabetes is defined as a fasting blood glucose of 126 mg/100 ml or above. Blood glucose measured 2 hours after consuming 75 g of glucose is normally less than 140 mg/100 ml. Prediabetes is defined as a blood glucose level between 140 and 199 mg/100 ml 2 hours after a glucose load and diabetes is defined as a blood glucose of 200 mg/100 ml or above 2 hours after a glucose load. (American Diabetes Association at http://www.diabetes.org/type-1-diabetes.jsp )
Diabetes is a serious disease. Uncontrolled diabetes damages the heart, blood vessels, kidneys, eyes, and nerves. It is the leading cause of blindness in adults and accounts for 40% of all new cases of kidney failure and over 60% of non-traumatic lower-limb amputations.* In the United States today diabetes is a major public health problem, accounting for about $132 billion in direct medical costs and indirect costs due to disability, lost work, and premature death. There are three types of diabetes: type 1, type 2, and gestational diabetes, which occurs during pregnancy.
Type 1 diabetes occurs when the body doesn't make insulin
Type 1 diabetes is an autoimmune disease in which the body's own immune system destroys the insulin-secreting cells of the pancreas. Therefore insulin is no longer made in the body. Type 1 diabetes is usually diagnosed before the age of 30. It accounts for only 5 to 10% of diagnosed cases of diabetes. It is not known what causes the immune system to malfunction and attack its own cells but genetics, viral infections, exposure to toxins, and abnormalities in the immune system may play a role. In people with type 1 diabetes, levels of glucose in the blood remain high while many of the body's cells are starving for glucose because without insulin glucose cannot enter certain cells. Weight loss occurs with diabetes because glucose cannot enter cells so they are starved for energy. Fat is broken down for energy and ketones are produced. Some ketones are used as fuel, but when they are produced more rapidly than they can be used or excreted they cause a potentially fatal increase in the acidity of the blood called ketoacidosis.