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Why Would You Have High Blood Sugar If You Have Not Eaten in 12 Hours?

author image Beth Greenwood
Beth Greenwood is an RN and has been a writer since 2010. She specializes in medical and health topics, as well as career articles about health care professions. Greenwood holds an Associate of Science in nursing from Shasta College.
Why Would You Have High Blood Sugar If You Have Not Eaten in 12 Hours?
Make sure to check your blood sugar level. Photo Credit: Wavebreakmedia Ltd/Wavebreak Media/Getty Images

When humans eat carbohydrates, the body converts them to sugar. The sugar fuels every cell in the human body, but it’s important that sugar levels be neither too high nor too low. Low blood sugar, called hypoglycemia, can cause brain damage and even shock. High blood sugar, known as hyperglycemia, is another matter.

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About Blood Glucose

When you consume carbohydrates, the starches are digested in the small intestine. After entering the bloodstream, the starches, which have been converted into sugars during the digestion process, cause your blood sugar, or glucose, to rise. When the blood sugar increases, the pancreas secretes insulin. Insulin helps most tissues of the body absorb and use the sugar. Only the brain and liver are not dependent on insulin.


Since prolonged hyperglycemia can damage body cells, insulin is used to keep the blood sugar within a fairly narrow range. As the blood sugar falls – for example, several hours after a meal when you are starting to get hungry again – the liver releases glucagon, which increases the blood sugar until it is back within the desired range. This seesaw effect goes on constantly in the body, and if your metabolism is healthy, no problems occur.


Diabetes mellitus, usually known simply as diabetes, is a disease in which the process of glucose regulation is disrupted. The first problem occurs when the cells become more resistant to insulin. This is called metabolic syndrome and is often a precursor to full-fledged diabetes. Sometimes the pancreas can stop producing insulin suddenly; this is called type 1 diabetes. Or insulin production in the pancreas can slow down gradually – type 2 diabetes. The slowdown of insulin production and a decrease in the cells’ ability to respond to insulin can also happen together.

Fasting Blood Sugars

Once the production of insulin slows or stops, the blood sugar remains high all the time. When you have diabetes, your blood sugar can be high no matter when you last ate, because the glucose metabolism process isn’t working properly. This is actually how diabetes is diagnosed. A blood sugar test is done after a 12-hour fast when you have not taken anything except water. If your blood sugar is between 100 and 125 mg/dL, it’s considered pre-diabetes. A reading of 126 mg/dL or above means you have diabetes and should consult with a health care professional.

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