Understanding Fasting Insulin Blood Test Results

Learn how fasting insulin tests offer personalized insights for improved health. Understand the role of these tests in generating actionable recommendations tailored to your unique needs.

Michelle Darian
By Michelle Darian
Lucia Gcingca
Edited by Lucia Gcingca

Published March 19, 2024.

A man running on a street with a cell phone in the foreground

Fasting insulin provides a critical window into sustained energy levels and the early detection of chronic diseases, despite its absence from standard bloodwork.

Despite its relevance for healthspan, a fasting insulin blood test is currently an underused measure of metabolic health in preventive and proactive care. Let's take a look at its role in lowering your sugar levels and what you can do to optimize it.

What is insulin?

Blood sugar—glucose—fuels our cells, and insulin is a key hormone that regulates its levels. Carbohydrate-rich foods like grains, rice, fruits, and vegetables break down into it during digestion and dissolve into the bloodstream, which raises it. [1]

This rise in blood sugar prompts the pancreas to release insulin, acting as the key that unlocks cell doors for glucose entry. It promotes the storage of excess glucose in the liver, fat tissue, and muscles for later use. As cells absorb glucose, blood sugar levels return to normal, and insulin production subsides. [1]

A poster showing the different the roles of insilin.

What is insulin resistance?

Insulin resistance is a condition where cells in the muscles, fat, and liver become less responsive to insulin This means sugar struggles to enter your cells for energy, forcing the body to produce more and more insulin to compensate. [1]

Building on our previous analogy, resistance occurs when the "key" (insulin) no longer fits the "lock" (cell receptors) on muscle, fat, and liver cells. it prevents glucose from entering these cells for energy, causing it to build up in the bloodstream and leading to high blood sugar levels.

» Discover why insulin is your key to metabolism and healthspan

Insulin resistance, prediabetes, and type 2 diabetes

Insulin resistance is a hallmark of prediabetes and type 2 diabetes. However, fasting insulin tests are often overlooked during routine bloodwork, even for individuals with suspected metabolic issues.

Insulin resistance is a signature component of both prediabetes and type 2 diabetes. But the problem is that fasting insulin blood tests aren’t a part of routine bloodwork unless a metabolic concern has already been identified. Even in those cases, the test may not measure it.

Since insulin affects multiple organs, impaired function raises the risk of chronic diseases across various bodily systems. [1]

Note: Given its role in regulating blood sugar, fasting insulin is a valuable marker of metabolic health. It can help assess your risk for future problems. That's why InsideTracker now tests it as a part of its Ultimate Plan.

Insulin and metabolic health

Even after fasting—when blood sugar is naturally low—people with poorer metabolic health tend to have consistently higher levels of it than those who are healthy. This effect suggests their bodies are working harder to manage glucose, which is a potential sign of underlying issues.

Did you know?

Alarmingly, an estimated 1 in 3 Americans has prediabetes, and 1 in 10 has type 2 diabetes—conditions characterized by high blood glucose and hemoglobin A1c levels. [2]. Plus, a concerning 20% of individuals with diabetes remain undiagnosed.

What is a fasting insulin blood test?

For an accurate picture of your body's insulin production, a fasting insulin test requires a 12-hour fast beforehand. It eliminates the temporary fluctuations caused by food intake and provides a reliable baseline measurement.

The reference range for a fasting insulin blood test

Unlike most blood tests, fasting insulin levels lack a universally accepted reference range. While some labs provide it, it's important to discuss your results with your doctor for personalized interpretation. This is because optimal scope can vary based on the person. factors.

InsideTracker determined the reference range for fasting insulin based on findings from both longitudinal and cross-sectional studies.

They investigated insulin levels in a healthy population free of chronic diseases that impact lifespan—such as all-cause mortality, cancer, metabolic syndrome, and more. [3] Maintaining insulin levels between 2.55 and 18.4 μIU/mL is generally recommended. [4]

» Learn more about what to expect during a blood draw

Interpreting fasting insulin blood test levels

A fasting insulin blood test should always accompany a fasting blood glucose test. Here’s how to interpret these test results. [1]

Fasting blood insulinFasting blood glucoseInterpretation
HighHighElevated fasting insulin and glucose levels can indicate that your cells are insulin resistant, requiring lifestyle or medical intervention.
OptimalHighYou may consider lifestyle interventions to improve blood glucose and continue monitoring insulin and glucose levels.
High or optimalLowSeek care from a medical provider to address low blood glucose levels (<65 mg/dL).
LowHighLow levels of insulin can result in increased blood sugar levels. Low levels of insulin may also indicate underlying health issues. It's always recommended that you discuss low insulin levels with your physician.

Note: Elevated blood sugar levels (>100 mg/dL) are more common than you think. About 13% of males and 7% of females who test with InsideTracker discover that they have high fasting glucose.

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What happens when the body doesn’t produce enough insulin?

Severely low insulin production, often caused by dysfunction in the pancreas, can trigger type 1 diabetes. [1] In this condition, the body struggles to use blood sugar for energy, leading to chronic high blood sugar levels and potential health complications.

Unusually low insulin levels can also be a sign of other health issues like hypopituitarism or pancreatic disease. Regardless of the cause, low insulin requires evaluation by a healthcare professional for proper diagnosis and management.

Here's where things go awry: even though cells become resistant to insulin, persistently high glucose levels continue to signal the pancreas to release more of the hormone. This constant push-and-pull between elevated blood sugar and increased insulin production fuels the fire of resistance, creating a self-perpetuating cycle. [5]

A diagram showing the relationship between insulin, glucose and type 2 diabetes

» Learn more about how blood sugar can change your body & brain

Symptoms of low insulin and insulin resistance

While physical symptoms may not always be present, both high and low insulin levels point to dysregulated blood sugar.

This is why monitoring fasting insulin levels, alongside blood sugar, is crucial for optimal health, even in the absence of immediate symptoms. Early detection of imbalances allows for proactive measures to prevent future complications.

Hyperglycemia (high blood glucose levels)

When the body doesn’t produce enough insulin, or the cells become resistant to its action, blood glucose levels can spike, known as hyperglycemia.

Hyperglycemia can lead to notable symptoms, such as: [1]

  • Frequent urination
  • Increased thirst
  • Unexplained weight loss
  • Fatigue
  • Confusion

Note: Not everyone in a hyperglycemic state will experience physical symptoms. A prolonged state of hyperglycemia can decrease symptoms experienced.

Hypoglycemia (low blood glucose levels)

While hyperglycemia is a concern, the opposite scenario—hypoglycemia—can also occur. It happens when the body produces too much insulin or lacks sufficient fuel—glucose—for energy.

Unlike hyperglycemia, hypoglycemia often presents with noticeable symptoms, such as:

  • Excess hunger
  • Sweating
  • Irregular heart rate
  • Fatigue
  • Dizziness
  • Blurred vision

*If you’re experiencing symptoms associated with hypoglycemia, seek immediate care from your medical provider. 

Risk factors for elevated fasting insulin levels

Studies show that several risk factors are associated with elevated insulin levels:

  • Visceral fat accumulation: Visceral fat stores excess lipids in the liver, leading to insulin resistance. [6]
  • Weight fluctuations: Weight fluctuations increase the risk of developing hyperinsulinemia (high insulin levels). [7] 
  • Weight gain: Studies show weight gain is associated with increased fasting blood insulin levels. [8]
  • Lack of quality sleep: Sleep disorders and a lack of sufficient quality sleep are associated with an increased risk of insulin resistance and the development of type 2 diabetes. [9]
  • Physical inactivity: A lack of physical activity increases the risk of becoming insulin-resistant. Significant research shows that physical activity is associated with improved blood glucose control. [10]
  • Age: Those over 45 are at an increased risk of becoming insulin-resistant due to aging-related metabolic shifts. [10] 
  • Race + ethnicity: People who are African American, American Indian, and Hispanic have an increased risk of insulin resistance. [10]

How high fasting insulin levels impact your longevity

Chronically high insulin and resistance can increase the risk of various chronic diseases that can significantly affect lifespan. It happens because blood sugar levels impact so many processes throughout the body.

Here's a closer look at some of the potential consequences:

  • Type 2 diabetes [11]
  • Cardiovascular disease [12]
  • Metabolic syndrome [13]
  • Polycystic ovary syndrome (PCOS) [1]
  • Alzheimer’s disease [14]
  • Cancer [3]
  • Liver disease [1]
  • Kidney disease [1]
  • Obesity [11]
  • All-cause mortality [15] 

Fasting insulin levels impact many other blood biomarkers

Fasting insulin levels offer a glimpse into your body's sensitivity and overall metabolic health. Research suggests its linked to increased inflammation—indicated by hs-CRP—and potentially altered liver function, reflected by ALT.

Note: Regular comprehensive blood tests are vital to assessing your health span. [16, 21]

Six ways to improve insulin resistance

The good news is that, like other blood sugar markers—fasting glucose and hemoglobin A1c—insulin levels are modifiable through lifestyle, nutrition, supplements, and exercise habits. 

Six general, science-backed ways to improve elevated fasting insulin levels include:

  1. Eat foods high in soluble fiber [22]
  2. Take a 5-minute walk every hour [23]
  3. Try cold water swimming [24]
  4. Take a chromium supplement [25]
  5. Take a folate supplement [26]
  6. Get 7-9 hours of quality sleep each night [27]

How to get your fasting insulin levels measured

While not typically included in a standard blood panel due to insurance limitations, fasting insulin is a valuable marker of metabolic health and potential lifespan.

Unlike blood sugar, which fluctuates throughout the day, fasting insulin provides a snapshot of your baseline production. By understanding how the body regulates glucose, you can take proactive steps to optimize your health through lifestyle choices.

InsideTracker now offers fasting insulin as part of its Ultimate Plan and Blood Results Upload Subscription. You'll then receive personalized, science-backed recommendations aimed at helping you live healthier and longer.


[1] https://pubmed.ncbi.nlm.nih.gov/34203830/

[2] https://www.cdc.gov/diabetes/library/spotlights/diabetes-facts-stats.html#:~:text=Key%20findings%20include%3A,t%20know%20they%20have%20it [3] https://pubmed.ncbi.nlm.nih.gov/28390156/ [4] https://testdirectory.questdiagnostics.com/test/home [5] https://pubmed.ncbi.nlm.nih.gov/16278749/ [6] https://pubmed.ncbi.nlm.nih.gov/22327367/ [7] https://pubmed.ncbi.nlm.nih.gov/12664081/ [8] https://pubmed.ncbi.nlm.nih.gov/29392827/ [9] https://pubmed.ncbi.nlm.nih.gov/24011890/ [10] https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance#develop [11] https://pubmed.ncbi.nlm.nih.gov/32819363/ [12] https://www.sciencedirect.com/science/article/abs/pii/002604959290088R [13] https://pubmed.ncbi.nlm.nih.gov/27748199/ [14] https://pubmed.ncbi.nlm.nih.gov/27432942/ [15] https://pubmed.ncbi.nlm.nih.gov/36030344/ [16] https://pubmed.ncbi.nlm.nih.gov/35190401/ [17] https://pubmed.ncbi.nlm.nih.gov/31891229/ [18] https://pubmed.ncbi.nlm.nih.gov/21521874/ [19] https://pubmed.ncbi.nlm.nih.gov/19439511/ [20] https://pubmed.ncbi.nlm.nih.gov/28376939/ [21] https://pubmed.ncbi.nlm.nih.gov/15047639/ [22] https://pubmed.ncbi.nlm.nih.gov/35807808/ [23] https://pubmed.ncbi.nlm.nih.gov/19470610/ [24] https://pubmed.ncbi.nlm.nih.gov/27376416/ [25] https://pubmed.ncbi.nlm.nih.gov/32730903/ [26] https://pubmed.ncbi.nlm.nih.gov/34371867/ [27] https://pubmed.ncbi.nlm.nih.gov/21836106/