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Writer's pictureMoran Sciamama-Saghiv

OMG! WHAT'S YOUR FBG?

Updated: Oct 23, 2023

HOW SWEET OF A DEAL ARE YOU???

FASTING BLOOD GLUCOSE by Dr. Saghiv

The average untrained person has about 70-100 grams of glucose roaming free in their blood stream (tissue), about 70-100 grams of glucose in their liver, and about 400 grams stored in their skeletal muscles. An athlete will add about 100 grams more to their stored glucose in their skeletal muscles.


Any excess glucose should turn into fat reserves, unless there is a pathology (a disease, clinical condition, or syndrome) preventing that from happening. Since eating "floods" the body with carbs and glucose, it complicates the ability to diagnose a person with diabetes, compared to measuring their fasting blood glucose (FBG). In addition to being used as a medical criteria for the diagnosis of diabetes, we use a person's fasting blood glucose as an indicator for exercising the person and/or exercise-testing the person.


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There are fasting blood glucose (FBG) ranges that support exercising the person with no safety or medical concerns, there are fasting blood glucose (FBG) ranges that support exercising the person with no safety or medical concerns as long as they increase their fasting blood glucose levels by taking a snack prior to exercising, and there are fasting blood glucose (FBG) ranges that contradict exercising the person (we will not exercise them).


Commonly, a fasting blood glucose concentration of equal or more than 126 mg/dL is the medical criteria for being diagnosed as a person with diabetes. Fasting blood glucose should be measured after preferably 8 hour with no consumption of food or liquids that would elevate glucose levels. Before diagnosis of a disease, it is best to base the diagnosis upon more than one measurement under the same conditions.


In order to exercise or exercise test a person without any concerns arising from their fasting blood glucose levels, we want them to have a fasting blood glucose level of 100-250 mg/dL and be without symptoms (asymptomatic); Special situations that require further consideration or actions taken before a person can be exercised and/or exercise test include:

  • If fasting blood glucose level is 250-299 mg/dL and at the same time ketones is 0.6 or less, exercise may be allowed according to professional’s decision. Exercise intensity will be limited to moderate (85% of maximal heart rate) at most. The person should be without symptoms (asymptomatic).

  • If fasting blood glucose level is 71-100 mg/dL without symptoms (asymptomatic), the person should be given a 15-20g snack with sugar.

  • If fasting blood glucose level is 51-70 mg/dL without symptoms (asymptomatic), the person should be given a 15-20g snack with sugar, and must wait at least 15 minutes before exercising.

  • If fasting blood glucose level is 50 mg/dL or less without symptoms (asymptomatic), the person should be given a 30-40g snack with sugar, and must wait at least 15 minutes before exercising.

  • A person suspected of being symptomatic (showing symptoms) or actually is symptomatic should not be exercised or exercise tested until cleared by a physician.

  • A person seeking to leave the lab after being exercise tested should have a fasting blood glucose level equal or greater than mg/dL without symptoms (asymptomatic).


Although fasting blood glucose is preferred as the criteria to diagnose a person with diabetes, criteria for blood glucose two hours after a 75 gram glucose load exist. Accordingly and under these conditions: 1) less than 140 mg/dL is considered normal; 2) 140-199 mg/dL is considered glucose impaired; 3) equal or greater than 200 mg/dL meets the criteria to be diagnosed with diabetes. Once more, based on at least two different measurements under similar conditions (two separate days preferred).


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