Why is Fasting Blood Sugar Important?

why is fasting blood sugar important

A fasting blood sugar test is a common diagnostic test prescribed during a doctors visit. Many of us have personal experience with this test, but how does fasting glucose help us measure of our health? Fasting blood sugar, or fasting glucose, is the amount of glucose in your blood after you have gone without food for eight hours or more. Knowing your fasting glucose level can help you understand your risk for diabetes and other health issues, and can be an important tool for managing your overall health. In this blog post, we'll explore what fasting glucose is, why it matters, and how to keep your levels in check.

What is Fasting Blood Sugar? 

what is fasting blood sugar

Fasting Blood Sugar (FBS) is the amount of glucose (sugar) in your blood after not eating or drinking anything (other than water) for at least eight hours. Glucose is a vital source of energy for our body and brain. However, too much or too little glucose can be a sign of poor metabolic health. Fasting blood sugar is an essential measurement used to assess blood sugar control.

Fasting blood sugar can indicate if an individual has diabetes, pre-diabetes, or normal blood sugar levels. This test can also help healthcare professionals identify and manage potential health risks related to blood sugar control. In the following sections, we will explore how FBS is measured, what the normal blood sugar levels are, and why FBS is important for our health.

How is Fasting Blood Sugar Measured?

how is fasting blood sugar measured

Fasting blood sugar is measured by drawing a blood sample after a person has fasted for at least eight hours. This test provides a baseline for glucose control, and can reveal abnormalities in blood sugar levels. The test is usually performed in the morning before breakfast, when blood sugar levels are at their lowest.

The results of this test are crucial in determining blood sugar control. If the results indicate high levels of glucose, it may indicate prediabetes or diabetes. Prediabetes is defined as a fasting blood sugar level between 100 and 125 mg/dL, while diabetes is diagnosed if fasting blood sugar is greater than 126 mg/dL. Conversely, low levels of glucose may indicate hypoglycemia, which can also be dangerous if left untreated.

Regular monitoring of fasting blood sugar levels can help individuals manage their glucose control and prevent serious health complications such as diabetes, heart disease, and stroke. If you are at risk for any of these conditions, talk to your doctor about testing your fasting blood sugar levels and creating a plan to maintain healthy levels.

What are Normal Fasting Blood Sugar Levels?

When we talk about normal fasting blood sugar levels, we are referring to the amount of glucose in the blood after an individual has fasted for at least eight hours. It is usually easiest to take this test in the morning before breakfast since we have naturally fasted during sleep.

The American Diabetes Association recommends a target range of 80-130 mg/dL for fasting blood sugar levels. However, individual targets may vary based on factors such as age, overall health, and personal medical history.

It's important to note that these target levels may differ for individuals with diabetes or prediabetes. In these cases, it's essential to work with a healthcare provider to determine individualized goals and treatment plans.

Keeping blood sugar levels within a healthy range can help prevent a range of health issues, including diabetes, heart disease, and stroke. If you're concerned about your fasting blood sugar levels, speak with a healthcare professional to discuss your options.

Why is Fasting Blood Sugar Important for Health?

Fasting blood sugar is an important indicator of our overall health and can help identify potential health risks. When our blood sugar levels are too high, it can indicate a condition known as hyperglycemia, which is commonly associated with diabetes. If left untreated, diabetes can lead to serious health complications such as obesity, heart disease, kidney disease, and nerve damage. On the other hand, low blood sugar levels, or hypoglycemia, can also be dangerous if not managed properly. It can cause symptoms such as confusion, dizziness, and even loss of consciousness.

By regularly monitoring our fasting blood sugar levels, we can detect any abnormalities early on and take necessary steps to manage our blood sugar control. This may include making changes to our diet, increasing physical activity, or taking medications as prescribed by a healthcare professional. By maintaining healthy fasting blood sugar levels, we can improve our metabolic health and reduce our risk of developing diabetes. It is important to work with our healthcare provider to establish personalized goals and treatment plans based on our individual health and medical history.

What to do Before a Glucose Test

If you have been advised to have a fasting glucose test, there are certain things you need to keep in mind before you go for the test. First and foremost, it is essential to ask your healthcare provider about how long to fast before blood work. Generally, a fasting period of at least eight hours is recommended, which means that you shouldn't eat or drink anything, except water, for eight hours before the test.  This means that you will need to have your last meal or snack the night before the test and avoid eating or drinking anything except water until after the test is done.  Be sure to follow the fasting instructions for blood work given by your healthcare provider.

In addition to fasting, you may also be advised to avoid certain medications or supplements before the test, as they can affect your blood sugar levels and provide inaccurate results. Therefore, it is important to follow your healthcare provider's instructions carefully and inform them about any medications or supplements you are taking.

It is also essential to stay hydrated during the fasting period and drink plenty of water. Dehydration can affect the results of your glucose test, so make sure to drink enough fluids before the test. Drinking water is generally allowed during the fasting period, but other liquids such as juice or coffee are not allowed.

By following these simple tips, you can ensure that your fasting glucose test provides accurate results and helps your healthcare provider to diagnose and manage any potential health conditions related to high or low blood sugar levels.


What Happens if Fasting Blood Sugar is too High or too Low?

Elevated fasting blood sugar can be caused by a variety of factors including: lack of exercise, poor diet, stress, lack of sleep, genetics, thyroid disorders, or air pollution. Since some of these factors, like stress and sleep, can change day to day it is important to look at multiple tests and consult with your healthcare professional in order to have an accurate picture of your metabolic health.

When fasting blood sugar levels are too high, it can indicate the presence of diabetes. In the short term, high levels of blood sugar can cause symptoms such as frequent urination, excessive thirst, blurred vision, and fatigue. In the long term, uncontrolled high blood sugar levels can lead to complications such as nerve damage, kidney damage, and an increased risk of heart disease.

On the other hand, if fasting blood sugar levels are too low, it can lead to hypoglycemia. Symptoms of hypoglycemia include dizziness, shakiness, confusion, and in severe cases, loss of consciousness. Hypoglycemia can occur in people with diabetes who take insulin or other blood sugar-lowering medications, as well as those who skip meals or exercise vigorously without adequate carbohydrate intake.

What Other Tests are Usually Run with Fasting Blood Sugar? 

what tests are run with fasting blood sugar

In addition to measuring fasting blood sugar, doctors may also order other tests to assess overall blood glucose control and risk for diabetes complications. These tests may include a hemoglobin A1c test, which measures the average blood sugar levels over the past three months, as well as a glucose tolerance test, which involves drinking a sugary solution and measuring blood sugar levels at timed intervals.

Furthermore, doctors may also check lipid levels, such as cholesterol and triglycerides, as high levels of these substances can increase the risk of heart disease and stroke. Additionally, a kidney function test may be ordered to monitor the health of the kidneys, as uncontrolled diabetes can damage these organs over time.

Overall, these tests provide a more complete picture of an individual's blood sugar control and can help doctors make informed decisions about treatment plans and lifestyle modifications.

A1c versus Fasting Glucose 

a1c vs fasting glucose test

As we just mentioned, hemoglobin A1c test is a common test that is run in conjunction with fasting blood sugar. Since both of these tests are blood tests used to assess blood sugar regulation, you may be wondering why doctors prescribe both.  While the A1c test measures the average blood sugar levels over the past three months, the fasting glucose test measures the blood sugar level after a period of fasting, usually eight hours.

While both tests are important in detecting high blood sugar levels, they measure different aspects of blood sugar control. A high A1c indicates that the blood sugar levels have been consistently elevated over a period of time, while a high fasting glucose level may indicate more immediate issues with blood sugar control.

It is possible for someone to have a normal A1c level but still have high fasting glucose levels. This is known as "normal HbA1c but high fasting glucose." Similarly, someone with high fasting blood sugar but normal A1c levels may have a condition called impaired fasting glucose.

In terms of accuracy, both tests are important and should be used in conjunction with each other for a complete picture of blood sugar control. Your healthcare provider may recommend different tests depending on your individual health history and needs.

While the A1c and fasting glucose tests measure different aspects of blood sugar control, both are important in detecting high blood sugar levels and maintaining overall health. It's best to consult with your healthcare provider to determine the best approach for your individual needs.

Tips for Maintaining Healthy Fasting Blood Sugar Levels 

tips for healthy blood sugar levels

Maintaining healthy fasting blood sugar levels is important for overall health and well-being. Here are some tips that can help keep your levels in check:

  1. Make informed food choices: Start reading food labels, be conscious of portion sizes, and make informed food choices that can improve your health. Incorporate foods that are high in fiber, such as fruits, vegetables, and whole grains. Avoid processed foods and foods that are high in sugar. To help get you started, check out our beginner’s guide to blood sugar control and 7 steps to better blood sugar.
  2. Exercise regularly: Physical activity helps to lower blood sugar levels by increasing insulin sensitivity. Aim for at least 30 minutes of moderate exercise per day. If you don’t know where to start, or want some ideas on how to exercise for metabolic health, check out our beginner’s guide to exercise for metabolic health (it also has some printable workout graphics to help get you started).
  3. Monitor your blood sugar levels: Regular monitoring of blood sugar levels can help you identify any spikes or dips in your levels, and adjust your diet and exercise routine accordingly. Our complete guide is a great reference on how to monitor your blood sugar levels at home.
  4. Manage stress levels: Stress can cause your blood sugar levels to spike, so it’s important to practice stress management techniques such as deep breathing, yoga, or meditation. Our recent blog, Stress and Blood Sugar Levels, is a great resource for tips on stress management.
  5. Stay hydrated: Drinking enough water can help flush out excess sugar from the body, and also helps with weight management. The body can perceive thirst as hunger so staying hydrated can help to keep you feeling full without the excess calories.

Take Home Tips

Here is a quick summary of some things to keep in mind before undergoing a fasting glucose test.

  1. Fasting: Most glucose tests require fasting for a specific period of time before the test. Typically, you will need to fast for at least eight hours prior to the test. This means avoiding any food or drinks, except for water, during this fasting period. It is important to adhere to the fasting time recommended by your healthcare provider, as eating or drinking anything other than water can affect your blood sugar levels and lead to inaccurate test results.
  2. Drinking water: While fasting, it is generally permissible to drink water. However, it is important to check with your healthcare provider to confirm if you can drink water before the glucose test. Other liquids such as juice, coffee, or tea should be avoided during the fasting period, as they can contain substances that may affect blood sugar levels.
  3. Medications: Before the glucose test, it is important to discuss with your healthcare provider about any medications you are currently taking. Some medications can affect blood sugar levels, and your healthcare provider may advise you on whether or not to take them before the test.
  4. What to eat before the test: As mentioned earlier, it is crucial to fast before a glucose test. Therefore, it is recommended to avoid eating any food during the fasting period. However, if you have any concerns or specific dietary requirements, it is important to consult with your healthcare provider for personalized instructions.


Remember, always consult with your healthcare provider for specific instructions regarding fasting and other preparations before undergoing a glucose test. Following these guidelines will help ensure accurate results and enable your healthcare provider to make informed decisions about your health.



Author: Dr. Colleen Gulick