Fasting insulin, why do we need to talk about it?

You may have heard of insulin, or you may still be brushing up on your knowledge of blood sugars and CGMs. Either way, this hormone is becoming famous, and it’s worth talking about why.

The principal role of the hormone insulin is to move glucose from food into cells for energy. Insulin in the media, pre the recent rise in continuous glucose monitors (CGMs), was in the early 20 ^th century when insulin was discovered as the cure for individuals with type 1 diabetes, a lifesaving treatment administered by injection.

Insulin is still a lifesaving treatment for both those with type 1 diabetes, for progressed type 2 diabetes and type 1.5 and type 3c diabetics. In more recent times, you may have become more aware of insulin through the use of continuous glucose monitors (CGMs), the promotion of the Zoe study, and awareness of how the stability of our blood glucose levels influence our energy levels, weight and overall health.

While CGM data is valuable and can be particularly helpful for those with diabetes, for those of us without diabetes but interested in our overall health, it doesn’t give us the full picture. It doesn’t tell us how much insulin we are producing. Your daily CGM glucose graph may be within range, but knowing how much insulin your body needs to produce to keep blood sugars within range is very valuable.

So why should we talk about fasting insulin? Is there value in testing? What will you learn from testing fasting insulin? 

Caroline Roberts, a nutritional therapist and health coach at Integral Wellness, an online functional medicine practice, explores the value of fasting insulin testing in relation to overall health.

Insulin resistance in human evolutionary history was a critical and essential part of normal homeostasis. Energy storage, regulated by the actions of insulin, was vital for human survival in times of food shortages and starvation. When mobilisation of the stored energy is required the action of insulin is inhibited (insulin resistance) so that glucose is released into and remains in the blood stream for use by those organs critical to basic survival.

In modern times, continuous high energy intake, low physical activity, and ongoing chronic stress can increase insulin secretion that promotes fat storage. Without times of starvation in developed countries, we no longer need that storage capacity. Increased fat deposits, particularly in our mid-section, create an inflammatory response, lipids overflow into other tissues, which in turn activates insulin resistance. This is a similar response to an infection or stress in evolutionary times.

Gaining insight into our fasting insulin levels can help determine our risk of developing insulin resistance long before a routine and more commonly used HbA1c (glycated haemoglobin) blood test does.

High fasting insulin has also been shown to contribute to systemic inflammation, high cholesterol, atherosclerosis, high blood pressure, non-alcoholic fatty liver disease (NAFLD - or the new name, Metabolic dysfunction-associated steatotic liver disease (MASLD)), high uric acid (think gout), polycystic ovary syndrome (PCOS), metabolic syndrome, and heart disease.

To provide some clarity around fasting insulin and what it may mean for you, here’s a quick fact list: 

Fasting insulin refers to the level of the hormone insulin in your blood after you've fasted (typically for 8–12 hours).

A test for fasting insulin is conducted through a blood test to determine how much insulin your body is producing when you are not actively digesting food. This can help assess your insulin sensitivity and whether you are insulin resistant or not, both of which are important measures of metabolic health.

Fasting insulin is a key measure of how well your body is managing blood sugar in a fasted state and can give valuable insights into your risk of metabolic conditions.

A fasting insulin test is valuable for guiding risk for high blood pressure, high cholesterol, cardiovascular disease, metabolic syndrome, fatty liver disease, and type 2 diabetes.

There is a significant variability between immunoassays for fasting insulin however functional medicine ranges suggest 2-6 uIU/mL for a healthy individual.

The lower your fasting insulin level, the more sensitive your body is to insulin. The less insulin your pancreas needs to release to keep blood glucose levels within normal limits, which is the test result you want.

If your fasting insulin level is lower than the test ranges, your pancreas may not be producing enough insulin. Remember, in health, homeostasis is about balance. 

If you have elevated fasting insulin level, also known as hyperinsulinaemia, it may suggest that your pancreas is having to produce higher than normal amounts of insulin to get cells to respond and manage blood sugars. Insulin resistance can occur when blood sugar levels have been rising too high for too long.

Insulin resistance is the most common cause of an elevated test result, cells become less responsive to insulin. The pancreas produces more and more insulin to try to gain a response and to try to keep blood sugars stable. Other factors include:

• Obesity and abdominal fat can disrupt the correct function of insulin which can lead to higher fasting insulin.
• A diet high in processed foods and refined carbohydrates elevates blood sugar levels, requiring more insulin to be released by the pancreas and fasted insulin levels.
• A sedentary lifestyle is linked to insulin resistance, lack of exercise and too much energy intake over time increases the risk of high fasting insulin and insulin resistance.
• Stress increases cortisol levels, cortisol influences blood sugar and insulin levels. If you are stressed over time cortisol will remain high, increasing blood sugars and the need for insulin.
• Hormone imbalances can disrupt insulin levels in those without type 2 diabetes. PCOS is often accompanied by elevated fasting insulin levels.
• If you have hypothyroidism this can impact metabolism and therefore fasting insulin levels.
• Sleep deprivation, medications, age, smoking, can also have an influence. 

Working with a registered nutritional therapist or health coach to look at dietary and lifestyle factors that may be influencing your result is a great place to start.

Simple dietary & lifestyle changes over time can lower fasting insulin and reduce your risk for associated diseases. 

1. Balance your blood sugars 

• Blood sugar levels are determined by what you choose to eat and how often you eat.
• Appetite control and stable energy levels are dependent on keeping blood sugars balanced.
• If you are overweight you are at more risk of insulin resistance. If you don’t know where to start with weight loss, read on for some key points.

2. Make some adjustments to your diet 

• Reducing the amount of carbohydrates you eat has been shown to improve insulin sensitivity and reduce the risk of insulin resistance.
• Foods high in carbohydrates break down to glucose more quickly than other macronutrients, causing a greater blood sugar rise and a greater need for insulin. 
• Reduce the amount of sugars in your diet; ultra processed foods are the main culprit, the foods you know won’t fill you up or keep energy levels stable. Fresh fruit is a great alternative as a dessert.
• Increase the amount of protein you eat; protein digests more slowly than carbohydrates, and doesn’t raise blood sugars, so there is less need for insulin. Pack your plate with colourful veggies; the fibre in vegetables slows digestive transit time, feeds our microbiome, keeps us satisfied for longer. They also include phytonutrients; powerful antioxidants that reduce inflammation–a contributing factor for a high fasting insulin result.
• Increase the amount of healthy fats in your diet; olive oil, nuts, seeds, olives, avocado, dairy. Like protein, healthy fats digest more slowly and release energy over time so less insulin is needed.

3. Move more 

• Movement can improve insulin sensitivity; exercising for 30 minutes a day, three to five times a week, can lead to permanent improved insulin sensitivity. 
• Building muscle improves blood sugar control; muscles store glucose and the more storage space you have for glucose the less likely it is to be stored as fat. Build enough muscle and you don’t need any insulin to move glucose into cells when you are exercising!

4. Manage stress 

• Stress can reduce insulin sensitivity; cortisol release during times of stress causes blood sugars to rise. Our body’s natural evolutionary response to danger requires a quick release of energy so that we can run away, fortunately there aren’t many situations we need to run from now but the natural response is the same no matter what the stressor is, and it impacts blood sugar control.
• We all have stress in our lives, learning how to manage it is key. Yoga and mindfulnesses have been shown to be effective techniques for stress management and support good blood sugar control.

If you are gaining weight, suffering with ongoing fatigue, suspect hormone imbalances (including peri menopause and menopause), or have cravings for caffeine and sugary foods, you may be experiencing insulin resistance. A fasting insulin test can be an extremely valuable insight into your metabolic health so that you can take action.

We always advise working with a qualified health professional to help you interpret results and guide dietary & lifestyle changes safely and sustainably.