The Truth About Fasting Blood Sugar: What Do the Numbers Really Mean?

Fasting blood sugar refers to the level of glucose in your bloodstream after you haven’t eaten for at least eight hours. It is a commonly used marker of metabolic health, often included in routine blood work during doctor visits.

This measurement can provide valuable insight into how your body manages glucose when not influenced by recent meals. However, even blood sugar levels considered “normal” may still pose risks to your health if they are consistently at the higher end of the spectrum.

Understanding Fasting Blood Sugar Levels

Healthcare providers often assess fasting blood sugar levels to understand how your body is regulating glucose. Generally, levels below 100 mg/dL are considered normal, while levels between 100 and 125 mg/dL may indicate an increased risk of metabolic dysfunction. Readings of 126 mg/dL or higher on two separate occasions are used to screen for diabetes.

The ADA Diagnostic Criteria are:

	Fasting Blood Glucose Levels	2-hr Post Meal Glucose Levels
Normal	< 100 mg/dL	< 140 mg/dL
Pre-Diabetes	100 to 125 mg/dL	140 to 199 mg/dL
Diabetes	≥ 126 mg/dL	≥ 200 mg/dL

However, fasting blood sugar alone does not always provide the full picture of metabolic health. Research suggests that insulin resistance, a condition where the body’s cells do not respond properly to insulin, can develop long before fasting blood sugar rises above the normal range.

This means that individuals with fasting blood sugar levels on the higher end of the normal spectrum (e.g., 90–99 mg/dL) may already be experiencing underlying metabolic challenges. Monitoring additional markers, such as fasting insulin or a measure of insulin sensitivity, may provide a more comprehensive view of metabolic health.

Why Is Fasting Blood Sugar Important?

Fasting blood sugar can reflect how your body maintains glucose balance during periods of fasting, such as overnight. It’s a key indicator of how efficiently your body processes and utilizes glucose. Consistently elevated levels, even within the normal range, may suggest that the body is working harder to maintain glucose balance.

Fasting blood sugar is an important indicator of metabolic health, but it doesn’t always provide the full picture. Elevated fasting blood sugar often reflects underlying metabolic challenges, such as reduced insulin sensitivity or the body compensating with higher insulin levels to maintain glucose balance. Research suggests that these issues can begin long before fasting blood sugar levels cross into the prediabetic or diabetic range, making early detection and intervention critical.

Over time, this strain can contribute to systemic inflammation, insulin resistance, and other complications. Recognizing these early signs can offer an opportunity to make lifestyle changes that support better metabolic health.

Monitoring fasting blood sugar alongside additional markers, such as fasting insulin or insulin sensitivity measures, may provide a more comprehensive view of metabolic health. This approach may help identify early signs of dysfunction that would otherwise go unnoticed if only blood sugar levels were considered. By addressing these challenges through targeted strategies like dietary adjustments, regular physical activity, and stress management, individuals may support healthier glucose regulation and reduce long-term risks.

Factors That Affect Fasting Blood Sugar

Many factors can impact fasting blood sugar levels, even for those without diabetes. These influences range from daily habits like diet and exercise to less obvious factors such as stress and sleep quality. Understanding how these elements affect your body is key to identifying areas where small changes can support healthier glucose levels. Below are some of the most common contributors:

• Diet: Meals high in refined carbohydrates or added sugars can overwhelm the body’s ability to regulate glucose over time. Focusing on nutrient-dense, whole foods may help support balanced blood sugar levels.
• Physical Activity: Regular movement, such as walking, strength training, or other forms of exercise, helps your body use glucose more efficiently and can stabilize blood sugar levels.
• Stress: Chronic stress raises cortisol levels, a hormone that can interfere with insulin sensitivity and glucose regulation. Managing stress through relaxation techniques or mindfulness can help decrease stress.
• Sleep: Poor sleep is linked to higher fasting blood sugar levels. Consistent, high-quality rest plays a key role in maintaining glucose balance and overall metabolic health.

By addressing these factors, you can take proactive steps to support your metabolic health and help to maintain stable blood sugar levels over time.

Why Normal but High Fasting Blood Sugar Levels Matter

Even if fasting blood sugar falls within the “normal” range, levels toward the higher end might indicate that the body is working harder to maintain glucose balance. These readings can serve as an early signal to explore lifestyle adjustments that may help maintain or improve metabolic health. For example, research has shown that individuals with fasting blood sugar levels in the higher-normal range may still be experiencing less insulin sensitivity, even in the absence of a diabetes diagnosis.

The American Diabetes Association (ADA) guidelines are often viewed as the standard for evaluating blood sugar levels, but emerging research highlights the potential risks of blood sugar levels that fall within the “normal” range. A 22-year study conducted on 1,973 healthy men aged 40 to 59—none of whom were diagnosed with diabetes—shed light on this issue. The men in this study all had fasting blood sugar levels below 110 mg/dL, which falls within the ADA’s range for nondiabetics.

Over the course of the study, 483 of the men had died, with 53% of the deaths attributed to cardiovascular disease. When the researchers analyzed the data by dividing participants into quartiles based on fasting blood sugar levels, a clear pattern emerged: men in the highest quartile, with fasting blood sugar levels above 85 mg/dL, had the highest statistically significant mortality rate.

To put this into perspective, the ADA does not consider fasting blood sugar to be in the prediabetic range until it reaches 100 mg/dL and doesn’t diagnose diabetes until it exceeds 126 mg/dL. Yet, this study indicates that fasting blood sugar levels above 85 mg/dL may independently predict cardiovascular mortality in otherwise healthy individuals.

The study concluded:

“Fasting blood glucose values in the upper normal range appear to be an important independent predictor of cardiovascular death in nondiabetic, apparently healthy middle-aged men.”

Tips for Supporting Healthy Fasting Blood Sugar Levels

While individual needs vary, there are some general strategies that may help support healthy fasting blood sugar. Choose nutrient-dense foods by prioritizing non-starchy vegetables, healthy fats, and quality proteins. Reducing refined carbohydrates, processed foods and added sugars may also be beneficial.

Stay active with regular exercise, such as walking or strength training (you can even do quick strength training at home). Incorporating relaxation techniques like meditation or deep breathing may help lower cortisol levels, which supports balanced blood sugar. Finally, aim for consistent, restful sleep, as it plays a critical role in maintaining healthy glucose levels.

If you notice consistent changes in your fasting blood sugar levels or have concerns about your metabolic health, it’s important to consult with a healthcare provider. They can perform additional assessments, such as measuring fasting insulin or conducting an oral glucose tolerance test, to provide a more comprehensive picture of your metabolic health. Partnering with a healthcare provider ensures that you receive personalized recommendations tailored to your unique circumstances.

Conclusion

Fasting blood sugar is an important marker of metabolic health that reflects how your body manages glucose during periods of fasting. While it’s just one piece of the puzzle, understanding its role and the factors that influence it can empower you to make informed lifestyle choices.