why does blood sugar rise when fasting

Stumped by high fasting blood glucose results? Join the club. "It just doesn't compute. When I snack before bed, my fastings are lower than when I limit my night nibbles," says Pete Hyatt, 59, PWD type 2. "It's logical for people to point the finger for high fasting blood sugar numbers at what they eat between dinner and bed, but surprisingly food isn't the lead villain," says Robert Chilton, M. D. , a cardiologist and professor of medicine at the University of Texas Health Science Center at San Antonio. The true culprit is compromised hormonal control of blood glucose levels. During the years (up to a decade) that type 2 diabetes develops, the hormonal control of blood glucose breaks down. Four hormones are involved in glucose control:
Insulin, made in the beta cells of the pancreas, helps the body use glucose from food by enabling glucose to move into the body's cells for energy.


People with type 2 diabetes have slowly dwindling insulin reserves. Amylin, secreted from the beta cells, slows the release of glucose into the bloodstream after eating by slowing stomach-emptying and increasing the feeling of fullness. People with type 1 and type 2 diabetes are amylin-deficient. Incretins, a group of hormones secreted from the intestines that includes glucagon-like peptide 1 (GLP-1), enhance the body's release of insulin after eating. This in turn slows stomach-emptying, promotes fullness, delays the release of glucose into the bloodstream, and prevents the pancreas from releasing glucagon, putting less glucose into the blood. Glucagon, made in the alpha cells of the pancreas, breaks down glucose stored in the liver and muscles and releases it to provide energy when glucose from food isn't available.


Christy Parkin, MSN, RN, CDE, responds: In the early morning hours, hormonal changes in your body will naturally cause blood glucose to rise. For people who don't have diabetes, the increase in blood glucose is offset by increased insulin production. For people with diabetes, this can be a problem. There are a couple of things going on that make your glucose rise in the morning. One of these is insulin resistance a condition that means your body's muscle and fat cells are unable to use insulin effectively to lower blood glucose. However, insulin resistance also affects how your liver processes, stores, and releases sugar, particularly at night.


The liver is supposed to release small amounts of glucose when you're not eating. But in type 2 diabetes, the liver dumps more glucose than is needed into the bloodstream, especially at night. So, while your hormones are causing a natural rise in blood glucose, your liver is releasing even more sugar into your system. And because your insulin resistance prevents your muscle and fat cells from using the sugar, your blood glucose level rises. Unlike mealtime blood glucose, which can be somewhat controlled by diet and exercise, high fasting blood glucose usually needs to be treated with medication. You should talk to your doctor about medications that can help you obtain good control. You may also want to read our September 2008 story ". "

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