Fasting insulin is a very useful, yet frequently missed, metabolic biomarker. It can catch metabolic issues years or even decades ahead of time compared to others like hemoglobin A1c, or fasting blood glucose, as it is a proxy for insulin resistance. Please read below to learn more about insulin, fasting insulin and insulin resistance, and ways to reverse high fasting insulin levels.
What is insulin, and why is it so important?
Insulin is a hormone manufactured and released by pancreatic beta cells when they sense high blood glucose levels. Insulin signals skeletal muscle, fat, and liver cells to uptake blood glucose for energy and storage. Insulin is the only hormone we have to lower blood glucose.
It is also the body’s main anabolic (building larger molecules from smaller ones) hormone. It can direct the synthesis of adipose (fat) tissue, along with protein molecules, and muscle tissue.
Insulin influences much more than our blood sugar. It impacts and regulates other hormones such as estrogen, thyroid, leptin, and ghrelin. Mood and cognition, cardiovascular health, weight loss/gain, menstruation, and even fertility is affected by insulin too.
The fasting insulin test, true preventative care
The fasting insulin test is a blood test that assesses your insulin levels in a fasted state. It typically requires an 8-12 hour fast.
The fasting insulin test is one of the best biomarkers for spotting early metabolic dysfunction. Elevated insulin can be present decades before high blood sugars ever pop up on a blood test. It is a critical indicator of insulin resistance, which is one of the main drivers behind prediabetes, type 2 diabetes, metabolic syndrome, cardiovascular disease, fatty liver, chronic inflammation, and obesity.
Fasting insulin is a surrogate marker of insulin resistance
Fasting insulin is a crucial biomarker because it reflects how well we use insulin, and whether we are insulin resistant. Insulin resistance is an altered cellular response to insulin’s prompts to take in glucose. This disruption occurs in liver, muscle, and fat cells.
When cells fail to respond normally to insulin, the pancreas pumps out more to get the memo to our cells to uptake blood glucose. Thus, when someone’s fasting insulin is high, this shows an impaired cellular reaction to insulin.
Unaddressed insulin resistance can develop into prediabetes and/or type 2 diabetes. Because of its anabolic and cell growth capabilities, high insulin levels result in body fat accumulation, elevated blood lipids, and cardiovascular risks as well such as coronary arterial hardening and thickening. Insulin can also cause water retention when present in large amounts. This can lead to or worsen high blood pressure.
What are considered ideal, normal, high, and low fasting insulin levels?
There are no set guidelines on what is considered high, low, or ideal fasting insulin levels.
Below are the cut-offs I use with my clients as an integrative and functional dietitian:
Fasting insulin levels chart
| Fasting insulin in mIU/mL | Assessment |
| 2-6 | Optimal |
| 7-9 | Good |
| 10 or above | High |
| <2 | Low |
What about fasting glucose and hemoglobin a1c?
Yes, fasting glucose and hemoglobin A1c are useful for identifying insulin resistance. If either are high, then it likely means you have some kind of insulin resistance and blood sugar dysregulation happening.
However, insulin resistance can go on for years, or even decades, before it elevates your blood sugar. Therefore, these are LATE indicators of insulin resistance.
Thus, fasting insulin is an EARLY indicator of insulin resistance, before a disease state sets in. Take this scenario for instance:
Client A’s blood test results:
Fasting blood glucose: 85 mg/dl
Hemoglobin A1c: 5.4
Fasting insulin: 15 mIU/ml
If you only tested for fasting blood sugar, or hemoglobin A1c, then everything would look normal, and the metabolic dysfunction would continue. But look at their high fasting insulin result. This person has likely been insulin resistant for some time now, and their body is over compensating by increasing their insulin output.
I hope this example illustrates why fasting insulin needs to be included in every cardiometabolic blood test panel, and why it is so important to track it often to look for trends.
Reasons behind high fasting insulin and insulin resistance?
- Genetics
- Trauma and/or chronic stress
- Lack of physical movement
- Low muscle mass
- Consuming too many refined foods, carbohydrates, and/or sugar
- Low fiber intake
- Poor sleep quality
- Lack of social connection, isolation, and/or loneliness
- High inflammation/hsCRP
- Nutrition deficiencies
- Abdominal obesity/high visceral fat
- Sluggish liver/fatty liver
- Gut microbiome imbalances
What can chronically high insulin lead to?
- Prediabetes/Type 2 diabetes
- High blood pressure
- High cholesterol and/or triglycerides
- Heart disease
- Coronary artery disease
- Certain types of cancer
- High inflammation
- Fatty liver
- Obesity and/or abdominal obesity
- Infertility
- Heavy/painful menstrual periods
- Hormone dysregulation
Signs and symptoms of high insulin levels/insulin resistance
| Fatigue | Increased thirst | More frequent urination | Dark, velvety skin patches on elbows, neck, armpits etc. |
| High blood pressure | High blood sugar | Elevated fasting insulin | Inflammation |
| Elevated blood lipids | Skin tags | Frequent colds/infections | Weight gain, especially abdominal |
| Increased hunger/sugar cravings | Numbness or tingling in hands/feet | Brain fog | Blurry vision |
*This list doesn’t cover every sign or symptom. They may overlap with other conditions as well. Also, some people may have no physical signs or symptoms of insulin resistance
Cultivating robust metabolic health
Household chores like washing dishes etc. are great ways to be more active throughout the day
We can address high fasting insulin levels and insulin resistance this through:
- Managing and resolving chronic stress and/or trauma
- Healing gut and liver health
- Engaging in regular physical activity at least 3-5 times per week
- Building lean muscle through strength training
- Doing NEAT (Non-Exercise Activity Thermogenesis) activities such as household chores
- Cultivating good sleep
- Lowering systemic inflammation
- Eating nutritious, and well-balanced meals
- Correcting nutritional deficiencies
- Eating adequate amounts of fiber (at least 30-35 grams/day), and protein
- Intermittent fasting
- Managing prescription medication side effects
- Reducing alcohol intake, or abstaining
We were never meant to rely on insulin alone to regulate our blood sugar
Building resilient metabolic health involves taking care of ourselves through eating good food, and doing health-promoting behaviors. However, we are not supposed to rely on insulin alone to manage our blood sugar. We have many hormones that increase blood glucose, such as glucagon, cortisol, adrenaline, and growth hormone. Yet, we only have one, insulin, that decreases it.
Thus, assisting insulin’s actions through doing the things listed above, will ensure that it isn’t solely responsible for blood sugar management. This way, it won’t build up in our blood, and our cells will be less likely to ignore its calls to take in glucose.
How to get your fasting insulin tested
You can ask your healthcare provider to add fasting insulin to your bloodwork order. Unfortunately, it is usually not covered by insurance carriers. You can also order it yourself through independent blood work companies like DirectLabs.com, or Rupahealth.com.
if you are looking for tasty and easy to prep snacks that can balance your blood sugar and insulin levels, then download my free e-book by clicking on the title, “5 satisfying snacks that can help reverse insulin resistance,
This blog post is for informational and educational purposes only. It is not medical advice. Please consult with your healthcare provider for personalized medical guidance.
