Katie Hull

3 mins read

Doctors regularly perform blood tests to assess their patients' health. You’ve probably had one yourself. The standard screening usually includes a full blood count, urea and electrolytes, serum lipids and fasting blood glucose. Various other tests (liver, thyroid, inflammatory markers, etc.) are frequently added to detect any abnormalities that suggest early-stage disease.

Yet, the blood test that tells us most about a patient's metabolic health is rarely performed. That is the fasting insulin test. Understanding why this test is so revealing requires a brief understanding of the role of insulin in metabolic disease.

The role of insulin

One of the underlying principles of our body's function is maintaining a stable blood glucose level (sugar). This is one of insulin’s major roles. When we eat carbohydrates, they’re broken down into glucose and absorbed into the bloodstream. The pancreas gland then releases insulin to drive the glucose out of the blood and into the cells, where it’s used as fuel.

Insulin has many other roles in the body, including promoting fat storage, especially the dangerous visceral fat around our organs, and promoting sodium reabsorption from the kidneys thus playing an important role in the development of hypertension.

Back to the primary role of insulin: The more carbohydrates we consume, the more insulin is secreted to prevent the blood glucose level from rising. Eventually, in many people, the body’s tissues become more and more resistant to the effect of insulin and thus require larger and larger amounts of insulin to maintain a normal blood glucose level. This is known as insulin resistance.

Rising blood glucose levels

Eventually, even this additional amount of insulin secretion is insufficient and the blood glucose level rises. When it reaches a certain level, the diagnosis of type 2 diabetes is made and then, and only then, are various measures undertaken to “treat this new disease”. These measures include diet, exercise and medications.

Type 2 diabetes does not develop overnight even though the diagnosis may become suddenly apparent. This process which commences with insulin resistance can take years, probably 10-20 years. 

Wouldn’t it be helpful if we detected those in the early stages of insulin resistance, which if no changes are made, may go on to develop type 2 diabetes, a disease that affects nearly 2 million Australians?

This is where a fasting serum insulin measurement can be so helpful.

Dr Brukner’s story

Let me describe my experience. I was a 60-year-old with a family history of type 2 diabetes but apart from being overweight, and borderline obese, I appeared to be in good health. My fasting blood glucose sat comfortably in the normal range. I thought I was metabolically healthy. 

The reality was that I was far from healthy. For the previous ten years, my regular blood tests had shown increased liver enzymes associated with non-alcoholic fatty liver disease (NAFLD). I also had markedly elevated triglycerides. I then had my serum insulin measured and it was markedly elevated, a condition we know as hyperinsulinemia. 

As I now understand, what was happening in my body was that I had developed insulin resistance, probably as a result of decades of a high carbohydrate diet, and my pancreas, in attempting to maintain normal blood glucose, was having to pump out large amounts of insulin. I was clearly pre-diabetic. I subsequently learned that a fatty liver was typical of this condition as was a high triglyceride level, both due to the excess carbohydrate being converted to fat both in the liver and pancreas as a consequence of high insulin levels. 

Fortunately, once I became aware of my condition and researched the topic at great length, I commenced a low carbohydrate diet as, after all, if there is less carbohydrate to ingest, then less insulin will be required to deal with it. After three months of a low carb diet, all my metabolic markers (liver enzymes, triglycerides and insulin) had returned to normal – and I had lost 13 kg. 

Preventing type 2 diabetes?

I would strongly advocate adding a serum insulin test to routine health screenings. Why wait for the diagnosis of type 2 diabetes, a horrible disease with disastrous long-term complications, when we can detect an early warning sign and take some measures (e.g. reducing the carbohydrate content of a patient’s diet to prevent the development of the condition?)

Why aren’t serum insulin measurements more widely performed? That's a good question and one that I have struggled to understand myself. I think it is probably due to our general lack of understanding of insulin's important role and our focus instead on lipids and cholesterol. There is also some concern that there may be variations from day to day in the serum insulin levels, but these should not deter us from conducting this vital test.

What is a “normal” serum insulin level? The laboratories have a “normal” range of 5-20 mIU/L, but this reflects average values rather than ideal ones. We recommend aiming for a level of less than 8mIU/L, with less than 5mIU/L as ideal. 

So, next time you have a patient requiring a routine blood test, include a fasting serum insulin test. It will be most informative.

Additional resources for patients

Consider recommending evidence-based dietary approaches, such as a low-carbohydrate therapeutic carbohydrate restriction (TCR) plan to your patients. The Defeat Diabetes downloadable TCR toolkit is available to support the successful implementation of lifestyle modifications into your patient’s plan. 

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