But how do we measure it and identify it?
Let's start with a basic biochemistry reminder. Insulin is an anabolic hormone made by the beta cells of the pancreas. It's purpose is to help us hold onto energy from the macronutrients we consume. Without insulin, we lose body mass (think about the initial presentation of a Type 1 Diabetic).
We often use the analogy that insulin is the "key" that unlocks the cells of our body, so glucose can enter the cell. Over time, with too much glucose exposure (combined with inflammation), the cells block insulin from doing its job. Usually, there are few to no symptoms associated with the subtle increase in glucose/insulin, which makes it difficult for practitioners to look for it. The body responds by making more insulin, which keeps blood glucose levels looking "normal" or "borderline", but eventually the pancreas can't meet the demand, and we start to see a rise in blood glucose levels. It can take months or years, but if we are not checking fasting insulin levels during routine blood tests, we will not catch this phenomenon in its early stages.
We cannot survive without glucose or insulin, but why would insulin suddenly stop working, in the case of insulin resistance? There is no single answer to this (pharmaceutical companies keep trying to find it!), but it starts with nutrition and lifestyle - with particular focus on carbohydrate intake and sleep. But these topics are for another blog post.
To make it easier to discuss the concept of IR with patients, here’s the analogy I like to give (using an excerpt from a classic I Love Lucy episode). Click here for the video. As you watch the video, imagine this:
Glucose = chocolate
Insulin = Lucy and Ethel
- Conveyor belt = bloodstream
As glucose production increases (represented by the increased speed of chocolate coming down the conveyer belt), Lucy and Ethel can initially keep up but eventually they have to do something with the glucose instead of packaging it up. The video is a perfect example of how insulin can not only keep up with all the chocolate/glucose production, but it also tends to lead to weight gain (as illustrated in the video with Lucy and Ethel stuffing the chocolate into their clothes/mouth). As you can imagine, eventually glucose gets by and builds up in the blood stream, and insulin gets “tired” of trying to keep up, leading to insulin resistance.
How do we test for insulin resistance?
First, identify who is at risk:
- Anyone who is obese (based on waist measurement and BMI) (see link below on how to measure)
- Anyone with sleep issues (and who snores - there are quick questions patients can answer that can identify those at risk for OSA)
- Family history of type 2 diabetes
- Having a family background that includes Hispanic, African American, American Indian, Asian American, Pacific Islander American, or Alaska native
- History of gestational diabetes during pregnancy
- Anyone with the parameters of metabolic syndrome (high blood pressure, elevated fasting glucose, low HDL, high triglycerides, large waistline)
- Anyone with polycystic ovarian syndrome (PCOS)
Next, initial testing:
- Fasting insulin (should be under 8)
- Fasting glucose
- Lipids, specifically triglycerides ("optimal" is under 100 mg/dL) and HDL
- LDL is not part of the criteria for IR, but I still encourage evaluation of lipid quality through an NMR, Boston Heart, or Cleveland Heart testing (much better than a quantitative evaluation)
- LFT's and GGT (IR loves to hurt the liver)
- Ferritin (should be between 50 and 200)
- 8am cortisol (should be over 12-15) - this is one way of indirectly looking for sleep problems, but it is far from perfect in a blood test (if it's low, ask about the patients sleep the night before the blood test, and ask about use of steroids over the last month)
There are many other ways to evaluate insulin resistance, but this can get everyone started (and most of the above should be covered by insurance). The biggest takeaway? Check the fasting insulin!
Wishing everyone great health, happiness, and a life at ease,
P.S. Click this link for further information about insulin resistance, prediabetes, and what can be done about it: http://www.niddk.nih.gov/health-information/health-topics/Diabetes/insulin-resistance-prediabetes/Pages/index.aspx