Blood sugar levels at least 8 hours after eating are essential data points for people with and without diabetes. Clinical guidelines say they should generally be 90 to 130 mg/dL, but that may vary.
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 required.
For those without diabetes, fasting glucose levels can help diagnose a condition if you’re experiencing symptoms.
Fasting glucose levels are also a standard protocol before any lab tests or bloodwork are taken during annual health checkups.
Your fasting glucose describes your glucose levels after at least 8 hours without eating or drinking 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:
| Age | Fasting blood sugar (mg/dL) |
|---|---|
| most adults | 90–130 |
| children | 90–180 |
| teenagers | 90–130 |
However, age isn’t everything regarding blood sugar and diabetes management.
Many other factors influence glucose levels before eating and at different 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.
Adults 65 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 and what clinical guidelines say about blood sugar levels after eating and at other times.
Both the ADA and the
- 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
To diagnose diabetes, healthcare professionals rely on what’s known as a “fasting plasma level.”
Fasting plasma level differs from a blood sugar check, which uses a fingerstick and a drop of blood. A doctor 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 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 determine if any changes are 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)
Fasting glucose levels are an essential criterion for getting 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 to limit how much they impact their blood sugars throughout the day.
In this
The study also found that intermittent fasting may be helpful as an auxiliary treatment to prevent developing other chronic diseases.
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 regimen.
That might mean taking more or less insulin, whether it’s a change in
Discuss blood sugar readings or concerns with a healthcare professional before changing 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.
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Learn more about hypoglycemia.
Hypoglycemia without diabetes
You can have low blood sugar levels even if you don’t have 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, but the person may also choose to eat a snack or drink a juice to boost their blood sugar more quickly.
Read more about non-diabetic hypoglycemia.
Consult a doctor or healthcare professional anytime you’re worried about your glucose levels.
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 lead to out-of-range glucose levels after eating.
Your fasting glucose levels after at least 8 hours without eating or drinking anything (except water) can be important data points for people with and without diabetes.
They can help you adjust your insulin rates or 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 vital if you’re concerned about hypoglycemia from not eating beforehand.