Understanding Fasting Insulin Blood Test Results

By Michelle Darian, MS, MPH, RD, July 14, 2023

Insulin_article1 (1)

Although standard bloodwork doesn't include fasting insulin, this biomarker is a key to sustained energy and an early warning sign for chronic disease. [1] And a fasting insulin blood test can reveal your levels. In fact, a blood test is often the first line of defense in measuring health. Despite its relevance for healthspan, a fasting insulin blood test is currently an underutilized measure of metabolic health in preventive and proactive care. 

Insulin is a biomarker of metabolic health—or the ease and efficiency at which the body breaks down, utilizes, and stores energy. Insulin is the hormone responsible for lowering high levels of blood sugar, but in people with poor metabolic health, insulin levels remain consistently higher (even when there’s no food in your system) compared to those who are metabolically healthy. Currently, many adults in the United States are not metabolically healthy. It’s estimated that 1 in 3 Americans has prediabetes and 1 in 10 has type 2 diabetes, which is characterized by high blood glucose and hemoglobin A1c levels. [2] The problem is that 1 in 5 people who have diabetes don’t know they have it. 

biomarkers for longevity

Insulin resistance is a signature component of both prediabetes and type 2 diabetes. But the problem is, fasting insulin blood tests aren’t a part of routine bloodwork unless a metabolic concern has already been identified—but even in those cases, it may not be measured. As insulin is involved in processes that span multiple organs, impaired insulin function is associated with an increased risk of several chronic diseases spanning various functions in the body. [1]

Because insulin is a key marker of metabolic health and healthspan, InsideTracker now offers a fasting insulin blood test as a part of its Ultimate and Blood Results Upload Plans.

While a fasting insulin test can reveal what your specific levels are, here’s what you need to know about interpreting and understanding your test results.

What is insulin?

Insulin is a key hormone that regulates blood glucose (sugar) levels. And what you eat plays a significant role in blood glucose levels. That’s because carbohydrate-containing foods (like grains, rice, fruits, vegetables, and legumes) are broken down to glucose in the digestive tract and are then absorbed into the bloodstream. [1]

This rise in blood sugar then triggers the pancreas to release insulin, and in turn lowers blood sugar levels by moving glucose into cells to be used for energy or to the liver, fat tissue, and muscles to be stored and used as energy for later. Insulin acts as the “key” that unlocks the door for glucose to enter those cells. As glucose enters your cells, blood glucose returns to its baseline level, and blood insulin levels follow suit. [1]


What role does insulin play in the body? 

Insulin acts on nearly every cell in the body and is involved in many processes and functions in addition to its role in regulating glucose levels. [1]

  • Metabolic function: Insulin helps to convert glucose from food into energy that fuels the body’s processes.
  • Growth and development: Insulin promotes the growth of bone, skeletal muscle, and tissue while supporting normal sex hormone function, muscle protein production, and vascular function.
  • Kidney function: Insulin helps to regulate sodium balance and homeostasis in the kidneys.
  • Cognitive function: Insulin helps to regulate cognitive functions like memory processing.
  • Liver function: Insulin helps create energy from sources like glycogen and fatty acids between meals.

roles of insulin

What is a fasting insulin blood test?

A blood draw is needed to measure fasting insulin levels. It’s recommended to complete a 12-hour fast prior to a fasting insulin blood test (to avoid expected fluctuations of the hormone from food) for a reliable metric of your body’s baseline insulin levels. 

What is the reference range for a fasting insulin blood test? 

Blood test results are often displayed against a reference range. Levels that fall outside of the reference range—say they’re too high or too low—should be addressed with your healthcare practitioner, as they may indicate a medical concern. However, there is no current standardized reference range for a fasting insulin blood test. 

InsideTracker determined the reference range for fasting insulin based on findings from both longitudinal and cross-sectional studies investigating insulin levels in a healthy population, free of chronic diseases that impact lifespan—like all-cause mortality, cancer, metabolic syndrome, and more. [3]

It’s generally recommended to maintain insulin levels between 2.55-18.4 μIU/mL. [4]

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


Fasting blood insulin Fasting blood glucose Interpretation
High High Elevated fasting insulin and glucose levels can indicate that your cells are insulin resistant, requiring lifestyle or medical intervention.
Optimal High You may consider lifestyle interventions to improve blood glucose and continue to monitor both insulin and glucose levels.
High or optimal Low Seek care from a medical provider to address low blood glucose levels (<65 mg/dL).
Low High Low levels of insulin can result in increased blood sugar levels. Low levels of insulin may also indicate underlying health issues. It’s encouraged to discuss low insulin levels with your physician.

Having elevated blood glucose levels (>100 mg/dL) is more common than you may think. About 13% of males and 7% of females who test with InsideTracker discover that they have elevated fasting blood glucose levels.

Who should get their fasting insulin levels tested?

Everyone—regardless of current diabetes status—should get a baseline measurement of their insulin levels and schedule routine follow-up tests every three to six months. 

What happens when fasting insulin levels are impaired?

The dysregulation of insulin can occur for two reasons: the body either can’t produce enough insulin, or it produces too much insulin to the point that it becomes ineffective. [1]

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

When the body can’t produce enough insulin, it’s typically because there is a dysfunction affecting the pancreas and the beta cells that produce the hormone. In the absence of adequate insulin, blood glucose levels can spike and remain elevated long after eating—leading to serious health conditions. 

Low levels of insulin may also indicate underlying health issues like type 1 diabetes, hypopituitarism, or pancreatic disease. Low levels of insulin should be addressed with a healthcare practitioner. [1]

What is insulin resistance?

Insulin resistance occurs when the body produces too much insulin to the point that it becomes ineffective. During insulin resistance, muscle, fat, and liver cells may not respond well to insulin to properly take up glucose from the blood like they should. [1]

Returning to the “key” analogy above, insulin resistance refers to the point at which insulin tries to act as a “key” to open the door to a cell, but the key no longer works. Because glucose isn’t moving into cells when they are insulin resistant, glucose accumulates in the blood, leading to elevated blood glucose levels (also known as hyperglycemia). 

But, the pancreas’s signal to produce insulin is high glucose levels. So, even though cells are insulin resistant, the continually elevated blood glucose levels still tell the pancreas to release insulin, resulting in raised blood insulin levels. The increase in insulin and elevated blood glucose levels further perpetuates insulin resistance, creating an undesirable cycle. [5]

Over time, insulin resistance can lead to prediabetes and the eventual development of type 2 diabetes.

Insulin resistance and prediabetes


Signs and symptoms associated with low insulin and insulin resistance

High or low levels of insulin indicate dysregulated blood glucose levels. It's altered blood glucose levels that can result in physical symptoms—which is what we'll discuss here. That said, it’s important to monitor blood glucose and fasting insulin levels even in the absence of experiencing physical symptoms. 

Hyperglycemia (high blood glucose levels)

When the body doesn’t produce enough insulin, or the body’s cells become resistant to insulin’s action, blood glucose levels can spike, also known as hyperglycemia. Hyperglycemia can lead to notable symptoms including: [1]

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

*It’s important to note that not all people who are currently in a hyperglycemic state will experience physical symptoms. A prolonged state of hyperglycemia can decrease symptoms experienced.

Hypoglycemia (low blood glucose levels)

When the body produces too much insulin or it doesn’t have sufficient fuel, blood glucose levels can drop, also known as hypoglycemia. Hypoglycemia can lead to notable symptoms like: [1]
  • 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 is associated with the storage of of 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 that weight gain is associated with increases in 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 is associated with an increased risk of becoming insulin resistant. Significant research shows that physical activity is associated with improvements in blood glucose control. [10]  
  • Age: Those who are over the age of 45 are at an increased risk of becoming insulin resistant due to metabolic shifts associated with aging. [10
  • Race + ethnicity: People who are African American, American Indian, and Hispanic have an increased risk of insulin resistance. [10]

How do high fasting insulin levels impact your longevity?

Because insulin and blood sugar levels impact so many processes throughout the body, insulin resistance is a contributing factor to multiple chronic diseases that impact healthspan. 

When left unaddressed, prolonged high insulin levels and insulin resistance may increase the risk of several conditions like:

  • 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 impacts many other blood biomarkers

Fasting insulin acts on nearly every cell in the body. So, it’s no surprise that scientific literature points to significant connections between fasting insulin levels and many other blood biomarker levels that span several processes. 

For example, higher fasting insulin is associated with increased hsCRP levels, indicating inflammation. The accumulation of fat that can accompany elevated fasting insulin levels may explain its relationship to elevated ALT levels as well. Blood biomarkers don't act in isolation—meaning changes in one biomarker can spark shifts in another. That's why it's critical to complete regular comprehensive blood tests to assess your healthspan.  [16-21]

6 ways to improve insulin resistance

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

There are many evidence-based ways to improve your fasting insulin levels. And the best way to know if a specific recommendation can help to improve your fasting insulin levels is to get your baseline measurement and generate your InsideTracker Action Plan to reveal your personalized recommendations. 

While your InsideTracker Action Plan includes a detailed breakdown of the best recommendations for you, here are six general, science-backed ways to improve elevated fasting insulin levels. 

  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 can you get your fasting insulin levels measured? 

Fasting insulin is not commonly included in a standard blood panel at your yearly physician’s visit, primarily because many insurance companies don’t cover the test for preventative screening. 

Because fasting insulin is a critical marker of healthspan, a blood sugar regulator, and can be impacted through lifestyle choices, InsideTracker now offers fasting insulin as part of its Ultimate and Blood Results Upload Plans. When you test fasting insulin levels, among dozens of other blood biomarkers related to healthspan, you can receive personalized, science-backed recommendations aimed at helping you live healthier 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/  


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