What Do Your Fasting Blood Glucose and Hemoglobin A1c Levels Mean?

Learn what fasting blood glucose and HbA1c tests reveal, and discover natural ways to keep your blood sugar in check.

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By Staff Writer
Caitlin Snethlage
Edited by Caitlin Snethlage

Published April 12, 2024.

A woman in a lab coat and blue gloves holding a test tube.

Blood sugar, the body's primary fuel source, needs to be kept in check for good health. Unhealthy habits can elevate your blood sugar, leading to prediabetes and type 2 diabetes. If left undetected, it may cause nerve damage, heart disease, and kidney failure.

Let's learn about the two most common blood tests used to detect abnormal glucose levels and ways to regulate them properly.

Key takeaways

  • Maintain a healthy weight
  • Limit red meat and sugar intake
  • Get 8 hours of sleep each night
  • Try a vegetarian diet (at least some days)
  • Maintain an exercise regimen
  • Incorporate nuts and beans into your diet
  • Make more meals at home
  • Practice mindfulness
  • Consider adding the right supplements for you.

What is fasting blood glucose?

Fasting blood glucose (FBG) is a test that measures the amount of sugar—glucose—circulating in your bloodstream after you haven't eaten or had anything but water for 8–12 hours. This ensures an accurate baseline reading of your body's ability to regulate blood sugar.

Blood sugar levels fluctuate throughout the day, especially after meals. 45–60% of calories come from carbohydrates, which the body breaks down into glucose for fuel. The pancreas releases insulin as the sugar enters the bloodstream.

An FBG test shows how efficiently your body manages the breakdown of glucose for fuel. Doctors use it to screen for prediabetes and diabetes, conditions that develop when blood sugar regulation becomes impaired.

A diagram of how insulin works.

Understanding FBG results

  • Normal range: 65–99 mg/dL
  • Prediabetes: 100–125 mg/dL
  • Diabetes: 126mg/dL or higher on two separate tests [1]

Healthy glucose levels are associated with better weight control, increased energy, and improved mood and cognition. High FBG after 8–12 hours without eating indicates an issue with glucose regulation and should be discussed with a physician.

What is Hemoglobin A1c?

As glucose builds up in the blood, it binds to hemoglobin, a protein found in red blood cells. Because it remains attached throughout its life—90–120 days—HbA1c provides insight into long-term exposure.

When FBG levels are high, physicians typically order a hemoglobin A1c—or HbA1c—test to gain insight into someone’s overall health. Unlike FBG ones, which only look at short-term well-being, the HbA1c value reflects the average blood glucose concentration over the past 3–4 months.

The higher the glucose level in the bloodstream, the more glucose will attach to hemoglobin; thus, the higher the HbA1c.

Understanding hemoglobin A1c ranges

  • Normal range: below 5.7%
  • Prediabetes: 5.7–6.4%
  • Diabetes: over 6.4% [1]

Note: As a rule of thumb, every 1% change in HbA1c results in an approximate 30 mg/dL change in glucose. [2] 

What causes HbA1c to increase?

Insulin is essential for adequately regulated glucose levels, but several factors interfere with the effect of insulin, either by weakening its signal or making cells less responsive to it. Some factors include:

Excess body weight

The accumulation of fat, especially visceral fat—the kind that surrounds our internal organs—directly interferes with insulin signaling. [3] This results in raised blood glucose and HbA1c levels and poses a risk for type 2 diabetes.

Note: Maintaining a healthy weight is imperative to well-controlled glucose. Even a 5–10% loss of body mass can significantly improve your levels. [4] 

Meat intake

Several studies consistently show a link between the consumption of meat and the incidence of type 2 diabetes. A 2015 meta-analysis examined its intake of over 50,000 people. They found that eating processed and unprocessed meat elevated fasting glucose levels. [5]

One explanation for this outcome may be due to the high saturated fat content in red meat. High intake increases the risk of developing type 2 diabetes. [6] It could also be due to the high iron content, which interferes with insulin signaling. [7]

Low fiber and high sugar intake

The majority of Americans do not reach the recommended intake of dietary fiber. It is a nutrient found in all plant foods, but humans do not contain the necessary enzymes to break it down for digestion. The fiber then goes undigested in the body, and foods high in it tend to keep us full longer.

Multiple studies show that a fiber-rich diet leads to an overall decrease in calorie intake and weight loss and reduces the risk of developing diabetes. You should aim for at least 25–38 grams of fiber daily—around 2 cups of black beans or 3 of raspberries.

Eating a lot of sugar is coupled with low fiber. It is found in juice, soda, and candy and is also added to salad dressings, nut butter, yogurt, and bread.

Note: Several studies indicate that excess sugar intake can result in increased fat, especially in the stomach region and liver, increasing HbA1c and the risk for diabetes. [8]

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Elevated glucose despite normal HbA1c

Because an FBG test measures your levels at a single point, it's more susceptible to your daily or weekly actions. If your HbA1c is normal but your blood glucose is above optimized, it could be due to:

Sleep deprivation

There’s evidence that poor sleep patterns impair glucose metabolism. People on restricted sleep demonstrate worsened insulin response to food, resulting in higher spikes.

In one study, sleep-deprived people had higher glucose and insulin levels after consuming breakfast than those who slept a healthy eight hours. [9] Other studies confirm this finding. [10–11] 


The body releases a steroid hormone called cortisol to activate our "flight-or-fight" responses to counteract acutely stressful situations. Cortisol stimulates the release of blood glucose by breaking down its storage form, glycogen.

Note: If you’ve experienced a stressful period, there's a good chance your blood sugar may be slightly higher than usual. 


Because glucose fluctuates after meals, we recommend fasting for 12 hours before getting a blood test for an accurate reading. This means only water, not even black coffee.

Note: Because people react differently to coffee, we suggest erring on the side of caution and sticking to water.

A line graph showing blood sugar and high blood sugar.

How to lower HbA1c and blood glucose levels

Maintaining a healthy weight, limiting meat intake, and sleeping well all contribute to better glucose control. However, several other lifestyle changes can help, too. 

Eat more plants, including beans and nuts

Vegetarian diets are inversely associated with the risk of developing type 2 diabetes. [12] A meta-analysis comparing nine experiments found that vegetarians consistently improved fasting blood glucose and HbA1c. [13]

Thanks to their high fiber content and low glycemic index—they don’t cause a blood sugar spike—beans stabilize glucose and insulin levels. [14] So, individuals with type 2 diabetes may notice significantly lower A1c if they increase their bean intake to at least one cup per day. [15]

Like beans, nuts are low glycemic and help regulate blood sugar levels. In a recent experiment, people who replaced some of their food with a serving of nuts saw improved glycemic control and HbA1c levels. [16]

Eating nuts has an inverse association with type 2 diabetes—people who include nuts in their daily lives tend to have a lower risk of developing diabetes. [17–18] 


Exercise directly improves blood glucose control, increases insulin sensitivity, and helps maintain a healthy weight. This prevents the development of type 2 diabetes.

Practice mindfulness

Incorporating mindfulness into your daily routine can improve both glucose and cortisol levels. [19] Start by practicing it for five minutes at a time and gradually increase this time to 30 minutes or more per day. 

Prep more meals at home

Takeout and restaurant food are typically higher in calories and saturated fat, which can increase blood glucose levels. [20] Cooking meals at home lets you control what goes into your food, leading to healthier levels. 

Consider supplements

Lastly, certain supplements may help lower your blood glucose. Always talk to your doctor before starting any new regimen, especially if you're already taking medication for diabetes.

Dive deeper: Blood sugar and total wellness

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[1] https://www.mayoclinic.org/diseases-conditions/diabetes/diagnosis-treatment/drc-20371451

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3912281/

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4038351/

[4] https://www.obesityaction.org/community/article-library/benefits-of-5-10-percent-weight-loss/

[5] https://www.ncbi.nlm.nih.gov/pubmed/26354543

[6] https://care.diabetesjournals.org/content/25/3/417.long

[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3648340/

[8] https://www.ncbi.nlm.nih.gov/pubmed/22190023

[9] https://www.ncbi.nlm.nih.gov/pubmed/21358855

[10] https://www.ncbi.nlm.nih.gov/pubmed/22844441

[11] https://www.ncbi.nlm.nih.gov/pubmed/25658017

[12] https://www.ncbi.nlm.nih.gov/pubmed/30229314

[13] https://www.ncbi.nlm.nih.gov/pubmed/29960809

[14] https://www.ncbi.nlm.nih.gov/pubmed/25061763

[15] https://www.ncbi.nlm.nih.gov/pubmed/23089999

[16] https://care.diabetesjournals.org/content/39/11/2065

[17] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6061153/

[18] https://www.ncbi.nlm.nih.gov/pubmed/24898241

[19] https://www.ncbi.nlm.nih.gov/pubmed/29076610

[20] https://www.ncbi.nlm.nih.gov/pubmed/27457635