Do you have symptoms of blood sugar imbalance, but bloodwork that comes back normal? You may need a fasting insulin test, which can reveal hidden problems with the way you regulate your blood sugar. Read on to learn how low & high fasting insulin may affect your health.

What is Insulin?

Insulin is a hormone produced by beta cells in the pancreas. When you eat, your digestive system breaks down carbohydrates into glucose, which is absorbed into the blood [1].

The rise in blood sugar stimulates the pancreas to release insulin, which moves glucose from the blood into cells in muscle and fat tissue. It also moves glucose into the liver, where it is stored as glycogen, a source of energy [1].


In type 1 diabetes (and advanced type 2 diabetes), the body cannot make enough insulin. This causes two big problems. First, the cells of the body become starved because they do not receive the glucose they need for energy. Second, rising blood sugar produces oxidative stress, which can lead to complications such as nerve damage or heart and kidney disease [2].

Insulin Resistance

Type 2 diabetes is characterized by insulin resistance: this is when you are producing enough insulin, but your cells are not getting the message. They are in essence “resistant” to the effects of insulin. The pancreas will try to compensate by releasing extra insulin, which massively raises insulin blood levels [1].

Besides type 2 diabetes, insulin resistance often develops in obesity, metabolic syndrome, heart disease, polycystic ovary syndrome (PCOS), and some other disorders [3].

Fasting Insulin Test

This test measures the insulin levels in your blood after at least 8 hours of fasting. A healthcare professional will collect a blood sample from your vein and send it to a lab for analysis. Other tests that may be performed to evaluate blood sugar and insulin levels include:

Why Is the Test Performed?

Fasting insulin is an important but often overlooked test that can help identify insulin resistance.

Insulin levels are usually out of order long before you can see any abnormalities in blood sugar levels. That’s why a blood sugar test might come back completely normal even if you are suffering from symptoms of blood sugar imbalance [4].

How to Prepare for the Test

You will normally be asked to fast (not eat or drink) for at least 8 hours before the test [5].

In healthy people, insulin levels are lowest after not eating for several hours. This is why fasting insulin tests are so reliable: if insulin is high after a fast, something may be very wrong [6].

Normal Range

The normal range of fasting insulin varies somewhat between labs, but 2 to 20 mIU/mL is considered normal by most [7, 8].

Children have lower fasting insulin levels than adults. An average child under 9 years of age produces between one-third and half the level of an average adult [8].

Low Insulin Levels


In healthy people, the most common cause of low insulin is fasting. Very-low-carb keto diets can also reduce insulin [6, 9].

The most common pathological cause of low insulin is type 1 diabetes, in which the pancreatic cells that normally produce insulin are destroyed. Inflammation in the pancreas (pancreatitis) can also lower insulin. Thus, an abnormally low fasting insulin result may indicate that your pancreas is damaged or dysfunctional [10, 11].

Insulin levels will also drop after pancreatectomy, a surgery to remove all or part of the pancreas. This procedure may be performed to transplant part of a donor’s healthy pancreas into a diabetic patient [12].

On the other hand, some SelfHacked clients naturally have lower insulin levels, even if they’re eating carbs and don’t have type 1 diabetes. They often complain they can’t gain weight. If you’re one of them, consider the following:

  • Vagus nerve stimulation, which increases insulin and is great for your health in general [13].
  • Reduce Stress. Epinephrine (adrenaline) lowers insulin, and it spikes when you’re stressed. An overactive nervous system is the cause of a lot of health issues we see in our clients [14].
  • Increase oxygen flow. Low oxygen is a common problem and it lowers insulin [15].


The most common cause of low insulin is type 1 diabetes. Symptoms of type 1 diabetes include [16]:

  • Excessive thirst
  • Frequent urination
  • Excessive hunger
  • Fatigue
  • Blurred vision
  • Numbness or tingling in the feet or hands
  • Sores that don’t heal
  • Weight loss

High Insulin Levels

Causes & Symptoms

1) Type 2 diabetes

Type 2 diabetes (T2DM) is the most common cause of high insulin. Prediabetes, an early stage of T2DM, is quite similar to insulin resistance, in which the body tries to compensate by releasing more insulin. In later stages, the pancreas becomes damaged, and insulin production drops. At this later stage, T2DM is very similar to type 1 diabetes, and symptoms are the same [17, 18].

2) Obesity

Obesity is linked to high insulin. In an observational study of nearly 4,000 people, higher fasting insulin levels were associated with weight gain. A marker of insulin resistance (HOMA-IR) was also associated with weight gain. Obesity likely leads to insulin resistance, which can, in turn, lead to T2DM [19].

3) Kidney disease

Insulin is broken down and excreted by the kidneys. When they are diseased, the kidneys are less effective at removing insulin, and thus it may build up in the blood. Kidney disease is a relatively rare cause of high insulin, but it may cause fatigue, itchy skin, frequent urination, blood in the urine, puffiness around the eyes, swollen feet, and muscle cramps [20, 21].

4) Insulinoma

Insulinomas are tumors in the pancreas, usually benign, that secrete excess insulin. Untreated, they can cause anxiety, visual disturbances, dizziness, hunger, heart palpitations, weakness, seizures, and even coma [22, 23].

5) Cushing’s syndrome

Cushing’s syndrome is a rare disease that may cause high insulin levels. It is characterized by excess cortisol production, and is usually due to a pituitary tumor. Cushing’s syndrome involves loss of muscle mass, and a diminished ability of muscles to take up insulin from the blood [24, 25].

People with Cushing’s disease gain weight in an unusual pattern: they develop a round “moon” face and a fatty hump on the neck, but their arms and legs stay thin. Other symptoms of Cushing’s include bruising easily, stretch marks, and muscle weakness [24, 25].

6) Acromegaly

Acromegaly is another rare disease that causes excess growth hormone and insulin-like growth factor-1 (IGF-1) levels. This disease is most often caused by a tumor in the pituitary gland. High growth hormone stimulates the production of insulin beyond normal levels [26, 27, 28].

Enlarged hands and feet are the hallmark of acromegaly, but it can cause other symptoms, including enlarged facial features, thickened skin, fatigue, muscle weakness, sleep apnea, impaired vision, joint pain, and reproductive dysfunction [26, 27, 28].

7) Drugs that increase insulin

Certain drugs may also increase insulin levels. These include:

  • Sulfonylureas (used for treating type 2 diabetes) [29]
  • Glucocorticoids (e.g. prednisone, hydrocortisone) [30]

Health Effects

1) Leads to Insulin Resistance

If you are insulin resistant, your body struggles to keep your blood sugar at bay. Your pancreas increases insulin production, but your tissues protest–they do not take insulin in and thus become “resistant.” It’s actually unclear if high insulin is a cause or a consequence of insulin resistance, but the two usually develop together [1, 3, 31].

2) Contributes to Metabolic Syndrome

Metabolic syndrome is a group of health problems that often occur together and increase one’s risk of type 2 diabetes and heart disease. You have metabolic syndrome if you have three or more of the following [32]:

  • High blood pressure
  • High blood sugar
  • Excess body fat around the waist
  • Low HDL cholesterol
  • High triglycerides

Many studies have linked metabolic syndrome with insulin resistance and high insulin. Some scientists even argue that metabolic syndrome is a consequence of insulin resistance. A review of 58 studies on metabolic syndrome revealed that almost everyone with this condition also has high insulin levels [33, 34, 35, 36].

Some scientists believe that insulin resistance directly causes metabolic syndrome. Whether one causes the other or not, almost everyone with metabolic syndrome has high insulin.

3) Suppresses Autophagy

Autophagy is the equivalent of detox on a cellular level. It’s a process by which cells collect, break down, and recycle junk products (debris). We rely on autophagy for good health, but amplifying it might also be key for life extension [37].

Under normal conditions, insulin prevents excess autophagy. However, when insulin levels are too high, it suppresses autophagy to an unhealthy extent [38].

When autophagy is not functioning correctly, cellular junk products can build up, leading to a range of problems including oxidative stress, metabolic syndrome, insulin resistance, and heart disease [39, 40, 41, 42, 43].

High insulin suppresses autophagy, the cell’s “detox” process. This can lead to a buildup of cellular junk products that cause oxidative stress and other health problems.

4) Increases Heart Disease Risk

High blood pressure and cholesterol mostly take the blame for heart disease. However, sugar and insulin might be as important. Evidence is mounting that insulin and insulin resistance could be at the center of the metabolic problems leading to heart disease [44, 45, 46].

According to several studies, high insulin levels predict heart disease, independent of blood pressure and cholesterol. While it is still not clear whether high insulin can cause heart disease on its own, it is heavily involved without a doubt [47, 48, 49].

We don’t know whether insulin directly damages the heart, but high insulin reliably predicts heart disease risk.

5) Increases Cancer Risk

High insulin increases insulin-like growth factor (IGF-1), which stimulates the growth of many types of cancer [50, 51].

What’s more, the conditions to which high insulin is tied, including metabolic syndrome and insulin resistance, are themselves linked with a higher risk of cancer [52, 50, 53, 51].

High insulin may also increase a person’s risk of dying from cancer. In an observational study of almost 10,000 people, those with higher insulin levels were more likely to die from cancer. This was true whether the individual was obese or not [54].

Similarly, a study of 2,000 people followed over 15 years found that those with higher insulin levels were more likely to die from cancer. This was again independent of other factors including whether they had diabetes, obesity or metabolic syndrome [55].

High insulin increases IGF-1, which stimulates the growth of many cancers. In multiple studies of thousands of people, high insulin was closely linked with the risk of dying from cancer.

6) Increases Risk of Alzheimer’s

Type 2 diabetes, insulin resistance, and high insulin levels are risk factors for developing Alzheimer’s disease (AD) [56, 57].

In an observational study of 683 people aged 65 years or older, the risk of AD doubled in those with high insulin. Another study of 980 people between the ages of 69 to 78 found a similar link between high insulin and AD [58, 59].

High insulin and insulin resistance may cause or contribute to AD in several ways. A study of 186 late-middle-aged people revealed that insulin resistance accelerates the deposition of beta-amyloid in the brain. As these proteins build up into plaques, cognitive symptoms like memory loss develop [60].

Insulin also increases Tau protein deposition, blood vessel damage, and inflammation in the brain [61, 62].

High insulin may promote the buildup of beta-amyloid and Tau proteins in the brain, thereby accelerating Alzheimer’s disease.

How to Decrease Insulin Levels

You can decrease your insulin levels naturally by making smart diet and lifestyle choices and adding a few supplements to your daily regimen.




Irregular Insulin Levels?

LabTestAnalyzer helps you make sense of your lab results and track them over time. It marks all your problematic labs and tells you how to get into the optimal range naturally. No need to do thousands of hours of research to understand your test results.

LabTestAnalyzer is a sister company of SelfHacked. The proceeds from your purchase of this product are reinvested into our research and development, in order to serve you better. Thanks for your support.


Fasting insulin measures the level of insulin in your blood. The normal range is 2 to 20 mIU/mL. Fasting insulin outside the normal range could indicate diseases such as diabetes. High insulin levels that are still within the normal range are unhealthy. They’re linked to insulin resistance and may increase the risk of heart disease, cancer, and Alzheimer’s.

To lower high insulin, exercise more, try fasting, and look into resveratrol and green tea supplements.

About the Author

Jimmy Julajak, MSc

MS (Psychology)

Jimmy got his MSc from the University of Copenhagen.

Jimmy is a psychologist and researcher. He is particularly interested in the workings of the brain and strategies for improving brain health. He believes that people shouldn't hand over the responsibility for their health only to their doctors. His aim is to empower each person with easy-to-understand, science-based health knowledge.

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