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Normal Blood Glucose Before Meals
Approximately 1.9 million Americans ages 20 and older were diagnosed with diabetes in 2010, according to the Centers for Disease Control and Prevention 1. Another 79 million were expected to have prediabetes in the same year. Keeping an eye on your blood glucose level is wise if you're at risk for either of these conditions, as is understanding what fasting blood glucose is and how it is affected by food.
Normal Fasting Glucose
Your blood glucose level is a key indicator of a problem with insulin production or blood sugar regulation in your body. The normal blood glucose level before meals, referred to as fasting blood glucose, should be between 70 and 99 mg/dL, according to registered dietitian Christine Wendt. Glucose in the blood comes from the food you consume each day and is used as an energy source. Some is stored in the liver for use during periods where you don't eat, such as during the night when you're sleeping.
- Your blood glucose level is a key indicator of a problem with insulin production or blood sugar regulation in your body.
- Some is stored in the liver for use during periods where you don't eat, such as during the night when you're sleeping.
Fasting Glucose Testing
What Happens to Sugar Levels in the Blood While Fasting?
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Fasting glucose tests are typically performed when you've not consumed any calories -- from food or beverages -- for at least eight hours. This would normally be done first thing in the morning prior to breakfast. Knowing your fasting glucose rate before the first meal of the day is important because it provides knowledge about how your body regulates blood sugar during the night. Physicians typically order the fasting blood glucose test during the diagnostic process for both prediabetes and diabetes.
- Fasting glucose tests are typically performed when you've not consumed any calories -- from food or beverages -- for at least eight hours.
Effect of Food
What -- and how much -- you eat directly impacts your blood sugar. Consuming carbs will cause your glucose level to rise the fastest and the most significantly. This is why carbs get the most attention when it comes to diabetes management. In addition, the more food you eat, the more your blood glucose will rise. Dietary habits may seem like a concern only when doing random glucose checks or postprandial tests, which are done two hours after you begin eating a meal. Yet what you eat can impact fasting levels as well. Eating large portions or high-carb foods just before bed affects glucose regulation during the night, thereby impacting your fasting glucose results the next morning.
- What -- and how much -- you eat directly impacts your blood sugar.
- Yet what you eat can impact fasting levels as well.
Abnormal Blood Glucose
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A fasting blood glucose level of 126 mg/dL or above is indicative of diabetes, although other conditions can cause high blood sugar as well. Endocrine conditions, such as Cushing's syndrome, can cause hyperglycemia. Stress and cardiovascular events cause high blood sugar as well. In contrast, pituitary tumors, kidney failure, hypothyroidism, malnutrition and cirrhosis of the liver may contribute to low fasting blood sugar. Low readings are below 90 mg/dL. A level below 70 mg/dL indicates a dangerous situation requiring medical attention, warns Dr. Barak Gaster of the University of Washington Medical Center.
- A fasting blood glucose level of 126 mg/dL or above is indicative of diabetes, although other conditions can cause high blood sugar as well.
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References
- Centers for Disease Control and Prevention: National Diabetes Fact Sheet, 2011
- Texas AgriLife Extension Service; Type 2 Diabetes Basics; Courtney J. Schoessow, MPH
- National Institute of Diabetes and Digestive and Kidney Diseases. Diabetes diet, eating, & physical activity. Published December 2016.
- American Diabetes Association. The big picture: Checking your blood glucose.
- American Diabetes Association. 6. Glycemic Targets: Standards of Medical Care in Diabetes-2020. Diabetes Care. 2020;43(Suppl 1):S66-S76. doi:10.2337/dc20-S006
- American Diabetes Association. 14. Management of diabetes in pregnancy: Standards of medical care in diabetes-2020. Diabetes Care. 2020;43(Suppl 1):S183-S192. doi:10.2337/dc20-S014
- Porcellati F, Lucidi P, Bolli GB, Fanelli CG. Thirty years of research on the dawn phenomenon: Lessons to optimize blood glucose control in diabetes. Diabetes Care. 2013;36(12):3860-2. doi:10.2337/dc13-2088
- American Diabetes Association. 5. Lifestyle management: Standards of medical care in diabetes-2019. Diabetes Care. 2019;42(Suppl 1):S46-60. doi:10.2337/dc19-S005
- Colberg SR, Sigal RJ, Yardley JE, et al. Physical activity/exercise and diabetes: A position statement of the American diabetes association. Diabetes Care. 2016;39(11):2065-2079. doi:10.2337/dc16-1728
- American Diabetes Association (ADA). Understanding A1C.
- Garber AJ, Abrahamson MJ, Barzilay JI, et al. Consensus statement by the American association of clinical endocrinologists and American college of endocrinology on the comprehensive type 2 diabetes management algorithm - 2019 executive summary. Endocr Pract. 2019;25(1):69-100. doi:10.4158/CS-2018-0535
Writer Bio
Previously working for the North Carolina Community College System, Rachel Morgan has been a freelance writer and editor for over six years. She has a bachelor's degree in public health as well as a master's degree in English.