A test for fasting insulin is one of the most important blood tests you can take; Dr. Joseph Mercola in fact believes that it’s the most important.
It’s important because it shows the degree of insulin resistance — the higher the number, the more insulin resistant. A really high number generally means type 2 diabetes. A number merely higher than normal means metabolic syndrome or pre-diabetes.
Insulin resistance is one of the main causes of chronic disease in the modern world, including heart disease, cancer, kidney disease, and of course diabetes. It either causes or is caused by obesity; the arrow of causation in that case is controversial. Being sedentary also leads to insulin resistance, and exercise can prevent it.
Insulin resistance is strongly associated with obesity, but normal weight people, especially those who are skinny-fat, can have it too.
Doctors don’t routinely test for fasting insulin; they normally do so only if they suspect diabetes.
I’ve had a few tests of fasting blood glucose that were high, in the range of 100 to 110. That’s an odd result, because I eat a low-carbohydrate diet and lift weights, and have a body fat percentage that i don’t know exactly but is no doubt <15%.
It’s probably due to the so-called dawn phenomenon, or physiological insulin resistance, which is normal. When on a low-carbohydrate diet, the liver can become insulin resitant in order to make glucose for the rest of the body. To be honest, the causes of the dawn phenomenon are not fully elucidated, and experts give varying explanations. But the fact is that many people who eat low-carb report it.
Not being clear on whether I should be concerned about my high fasting glucose, I decided to get a fasting insulin test from Life Extension.
Result: 2.9 µIU/ml. Normal range is 2.6 to 24.9. (On this scale, 1 µIU/ml = 6.9 pmol/L.) Ideal, according to Dr. Mercola and others I’ve read, is <3. The odds ratio for prediabetes rises sharply with increased fasting insulin.
My result was about as perfect as one could want. I think I’m going to live another few years.
Should I remain concerned about my fasting glucose test? Probably not; my non-fasting glucose is actually lower than my fasting glucose, which would seem to indicate, together with my insulin test, that I have no risk of diabetes. It would indeed be strange if I did have increased risk, for the reasons mentioned above: low-carb diet, weight lifting, low body fat, plenty of muscle too.
If you do have a high fasting insulin, then you need to get to work. Below are relative risks of hypertension, high triglycerides, and diabetes based on fasting insulin levels. (Source.)
You can order a fasting insulin test through Life Extension; blood is drawn at no extra charge at LabCorp.