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What is Glucose?

Glucose is a monosaccharide, meaning it contains one sugar molecule. It is considered a simple sugar since it can be easily absorbed by the body and used for energy and a major fuel source for the body. Glucose and be combined with other monosaccharides to create disaccharide compounds (two sugar molecules combined) or longer complex carbohydrates. Alternatively, glucose may be derived from the breakdown of carbohydrates. Glucose is formed by plants through the process of photosynthesis.

What are glucose levels?

Glucose is our body’s preferred source of fuel since it’s easy to break down. Once we consume glucose, which can be found in anything from bread to fruit, it’s detectable in our blood, as it’s carried to all the cells throughout our body which use it for fuel.

Our glucose levels are influenced by how much glucose our body makes from the foods we eat, as well as hormones that control it, like insulin. Our glucose levels change throughout the day, depending on when and how much we eat. They can also be influenced by stress, illness, or a lack of activity. Blood glucose levels are usually lowest right before mealtimes.   

What are normal glucose levels?

For most healthy adults, blood glucose levels vary throughout the day depending on when their last meal was eaten. This healthy range may also change as a person ages. Normal fasting glucose levels, or levels measure at least 8 hours after a meal has been eaten, are less than 100 mL/dL. Non-fasting or random glucose levels typically range from 80 to 140 mL/dL.   

Ideally, a healthy blood glucose level is under 99 milliliters per deciliter of blood before a meal, and around 140 mL/dL after a meal.

People with diabetes need to be careful and pay close attention to their blood glucose levels to ensure they’re able to dose their insulin accurately.  

For a diabetic, those numbers will look a bit different. Anything under 70 mL/dL before a meal, and 70-130 mL/dL after a meal is considered normal.

What is a glucose test?

A blood glucose test is a screening used to monitor for various types of diabetes, as well as other diseases. If you’re asked to do a glucose test, it usually begins with abstaining from food and drink for at least 8 hours before the test. After that, you’ll go into a lab or your doctor’s office, and they’ll draw your blood to test your fasting glucose levels. 

For other glucose tests, you’ll be asked to drink a sugary beverage before the blood draw, so they can measure your normal glucose levels. While it may be inconvenient to abstain from eating for this long, these tests are very helpful in diagnosing metabolic issues like diabetes or kidney disease.

Learn more about Glucose:

Photo of Kristin Ricklefs-Johnson

Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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