Fasting Blood Sugar Levels: Everything You Need To Know

Fasting blood sugar levels are checked to ensure that the body is properly absorbing sugar. Fasting blood sugar levels primarily serves to help diabetics (and also prediabetics) stay healthy by prompting them to get their sugar levels within the target range.

One should note here that the role of fasting blood sugar levels is not confined to this particular purpose as stated above. This fact has further instilled the need to gain more relevant facts regarding the importance of testing one’s fasting blood glucose levels.

Fasting Blood Sugar Level – Its Purpose And Role

To reiterate, fasting blood glucose levels help confirm if an individual is prediabetic or diabetic. This entails taking one’s blood sugar readings in a fasting state, or precisely, several hours after eating to gain a more accurate view of one’s glucose levels.

Fasting Blood Sugar Level - Its Purpose And Role

A fasting blood glucose test for a normal person should read below 5.7%. This knowledge has, therefore, invoked the need to follow specific guidelines on fasting blood glucose levels for prediabetics and diabetes in an upcoming section.

Guidelines For Fasting Blood Glucose Readings

Normal Fasting Glucose ReadingsBetween 70 mg/dL (3.9 mmol/L) and 100 mg/dL. (5.6 mmol/L). 
Fasting Blood Sugar Levels For PrediabeticsBetween 100 mg/dL (5.6 mmol/dL) and 125 mgl/dL (6.9 mmol/L).
For Diabetics126 mg/dL or higher (6.5 mmol/L and above).

Criteria For Checking Fasting Blood Glucose

Per WHO recommendations, people experiencing symptoms with either low or high blood glucose levels are most eligible to have these checked on a fasting basis.

While dizziness, sweating, palpitations, and blurred vision are highly associated with hypoglycemia, those suspected to have high sugar levels are prone to feel increasingly thirsty while experiencing dry mouth, frequent urination, tiredness, blurred vision, unintentional weight loss, and recurring infections of the bladder and skin accompanied by thrush.

Surprisingly, blurred vision associates itself with extremely high and low blood sugar levels.

However, it is the other symptoms that go along with these two conditions that help a physician discern who is suffering from hyper or hypoglycemia.

Methods For Checking Fasting Blood Sugar Levels

Patients with diabetes are usually advised to fast for a maximum of 12 hours (minimum being 8) before having their sugar levels checked. While this is the usual technique, it happens to be at the discretion of some physicians to decide on a time length at which patients should fast.

During this decisive phase, one cannot eat or drink anything other than water. This is because sugar is easily absorbed through food intakes rich in carbohydrates and fats.

However, consuming water during the fasting schedule will either help prevent sugars from going too high or decrease excess glucose levels, especially when one has had a heavy meal. One can usually get one’s fasting sugar levels checked in the morning before breakfast, also several hours after eating one’s food for the day.

Factors Affecting Fasting Blood Glucose Levels

Of note, three major factors contribute to influencing/affecting blood glucose levels in a fasting mode. These have included:

  • Contents of the last meal that a person has consumed: It can be undoubtedly stated here that one’s fasting blood sugar levels can be largely affected by the number of contents present on one’s plate. If these are specifically consumed hours before one starts to fast, one can only expect spiking glucose levels even when one has gone fasting.
  • Size of the meal taken before beginning to fast: A meal’s size is another factor affecting one’s fasting blood glucose levels. No matter the contents that one includes in one’s meals if their portion sizes are higher, then their chances of causing blood sugar rise during fasting are significantly high. 
  • The patient’s ability to produce and respond to insulin: It is common for hyperglycemic patients to be insulin-resistant than those considered hypoglycemic. While the former tends to experience insulin resistance typical of diabetes, the latter suffers from low sugar level symptoms due to taking diabetes medications on rigorous terms.

How Can Fasting Blood Glucose Tests Help Control Diabetes?

Checking one’s blood glucose readings on a fasting mode can effectively help bring sugar levels down to the normal/target range. This may, however, require medication intervention to assist in the process. The sugar levels revealed during fasting glucose levels will prompt the patients, especially the diabetics and the prediabetics, to consider making the necessary lifestyle changes.

Despite the issues faced with insulin resistance, considering portion sizes in their diet, exercise, and routine sugar checks, either on a fasting or non-fasting mode will expectantly help them control and maintain their levels within the normal range.

Read More:- Major Blood Sugar Drop Symptoms – Facts To Know!


Fasting blood sugar levels accurately helps determine whether one is a diabetic or prediabetic. The results derived from undertaking blood sugar tests on a fasting mode are more than likely to motivate patients with diabetes or those at risk of developing the condition to efficiently keep track of their sugar levels to prevent them from rising or going too low.

In saying so, glucose checked when fasting can even help those with hypoglycemia and symptoms related to the same. It is, therefore, advisable for the concerned patients to not resort to rigorous measures in the event of normalizing their blood glucose levels    


CDC (2023) Diabetes Tests. Available at: (Accessed: 11 September 2023).

Cronkleton, E. (2023) Fasting blood sugar (glucose): Normal levels and testing. Available at: (Accessed: 11 September 2023).

Cunha, J.P. (?) Does Drinking Water Increase Fasting Blood Sugar? Available at: (Accessed: 11 September 2023).

WHO (2023) Mean fasting blood glucose. Available at: (Accessed: 11 September 2023).

About the Author

Nicole Carter is a dedicated and passionate nutritionist, committed to helping individuals achieve their health and wellness goals through the power of proper nutrition. With a Bachelor's degree in Nutritional Science and years of practical experience.

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