Blood sugar levels at least 8 hours after eating are important data points for people with and without diabetes. Clinical guidelines say they should generally be 90 to 130 mg/dL, but that may vary.

Your blood sugar levels before you eat or drink any food are an important gauge for both those with and without diabetes.

People with diabetes use these fasting blood sugars as a starting point for how much insulin or medications they may need, or whether any dosage adjustments are needed.

For those without diabetes, fasting glucose levels can help diagnose a condition if you’re experiencing symptoms. These fasting glucose levels are also a standard protocol before any lab tests or bloodwork is taken during annual health checkups.

This article will explain fasting blood sugars, why they’re important, and what clinical guidelines say about these glucose levels for people with and without diabetes.

Your fasting glucose describes your glucose levels at least 8 hours since you’ve eaten or drank anything except water.

The American Diabetes Association (ADA) recommends, in its annual guidelines, a range for people with diabetes based on age as one key factor:

AgeFasting blood sugar (mg/dL)
most adults
(see guidelines)
children and teens
(see guidelines)
(see guidelines)
pregnancy and gestational diabetes
(see guidelines)

However, age isn’t everything when it comes to blood sugar and diabetes management.

Many other factors influence glucose levels before eating and at other times of the day and night. The ADA emphasizes individualized care and goals. Everyone’s glucose levels may differ based on many different aspects: from their overall diabetes management, complications they experience, other health conditions they live with, and the technology or tools they use.

Older adults who are 65 years of age and older may also have different glucose goals, including fasting glucose levels, because they may be more at risk of hypoglycemia.

Read more about age-based glucose levels as well as what clinical guidelines say about blood sugar levels after eating and at other times. Make sure to discuss with a diabetes and healthcare team any personal goals or preferences that you may have.

Both the ADA and Centers for Disease Control and Prevention (CDC) recommend the following for people without diabetes:

  • 99 milligrams per deciliter (mg/dL) or lower is normal
  • 100 to 125 mg/dL may mean you have prediabetes
  • 126 mg/dL or higher may indicate diabetes

In the diagnosis of diabetes, healthcare professionals rely on what’s known as a “fasting plasma level.”

Checking fasting plasma level is different from a blood sugar check, which uses a fingerstick and drop of blood, in that a doctor’s office or lab technician will draw your blood to check the glucose level within your plasma.

The measurement is considered more accurate than a fingerstick blood test. Many doctors and clinics prefer to have this fasting glucose test done in the morning before you’ve had breakfast.

Fasting glucose levels are important because they help determine whether you have diabetes or how you’re managing your condition if diabetes has already been diagnosed.

For example, people with diabetes rely on fasting glucose levels to help gauge their current management routine and figure out if any changes may be needed. Some of those adjustments may include:

  • whether you need more or less background insulin (basal rate)
  • if you need to adjust how much insulin you take to dose for food or for correcting high blood sugars (correction rate and sensitivity factor)
  • if your diabetes medication dosages need adjusting (for people with type 2 diabetes)

Additionally, fasting glucose levels are important criteria for anyone going to get lab or bloodwork performed. A standard protocol is to not eat or drink anything (except water) for at least several hours beforehand, which is why many clinicians and healthcare professionals prefer to have fasting glucose tests done in the morning before breakfast.

Some people also use intermittent fasting as part of their lifestyle and eating patterns in limiting how much they’re impacting their blood sugars throughout the day.

In this 2022 review of studies, researchers found that intermittent fasting can have benefits on blood glucose and lipids for people with metabolic syndrome or those experiencing insulin resistance. The study also found that intermittent fasting may be helpful as an auxiliary treatment to prevent other chronic disease development.

The varying fasting methods in this type of diet may include:

  • alternate-day fasting (consuming no calories on fasting days)
  • alternate day-modified fasting (consuming less than 25% of caloric requirements on fasting days)
  • time-restricted fasting (restricting food intake at specific times of the day)
  • periodic fasting (fasting on 1 to 2 days per week)

Intermittent fasting isn’t for everyone, and it’s always best to consult with a healthcare team before deciding what might be best for you.

If you’re a person with diabetes, your fasting blood sugars can be a way to decide if you might need to adjust your current regime.

That might mean taking more or less insulin, whether it’s a change in basal rate, correction rate, or sensitivity factor. It can be especially important if you’re starting insulin therapy and trying to find a starting point for basal-bolus rates.

Always make sure to discuss any blood sugar readings or concerns with a healthcare team before making any changes to your diabetes management plan, medications, or insulin doses.

Low blood sugars can be a concern for people with diabetes, particularly in the context of fasting glucose levels and levels overnight when you’re asleep.

Anything below 70 mg/dL is considered hypoglycemia by the ADA and other diabetes care guidelines worldwide, and blood sugars below 55 mg/dL are classified as more severe and clinically significant.

Learn more about hypoglycemia.

Hypoglycemia without diabetes

You can have low blood sugar levels even if you don’t live with any type of diabetes. For instance, you may not have diabetes, but your body can produce too much insulin. Overproduction of insulin can lead to symptoms such as shakiness, headache, or cold shivers.

Often these hypoglycemic events for people without diabetes will auto-adjust after a bit of time, but the person may also choose to eat a snack or drink a juice in order to boost their blood sugar more quickly.

Read more about non-diabetes hypoglycemia.

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Any time you’re worried about your glucose levels is a time to consult with a doctor or healthcare team.

If you’re experiencing high or low blood sugars before eating (or at any other time), you may want to discuss possible changes to your care plan.

The changes may include adjusting insulin correction amounts for the food you’re consuming, as it may not be accurate. You may also need to adjust your background insulin amounts if they’re leading to out-of-range glucose levels after eating.

Most importantly, don’t make any changes to your medication dosages or diabetes care plan without first talking with a healthcare team.

Your fasting glucose levels at least 8 hours since you’ve last eaten or drank anything (except water) can be important data points for both people with and without diabetes. They can help you adjust your insulin rates or diabetes medication dosages, as well as help diagnose diabetes, even if you’re not experiencing symptoms.

You should also try to fast before any lab or bloodwork is done, which can be important if you’re concerned about hypoglycemia from not eating beforehand.