How to measure metabolic health

In case you haven’t noticed, there has been an increased focus in science and medicine on the importance of maintaining good metabolic health.  This includes improving insulin sensitivity and metabolic flexibility – the ability to switch between glucose and fats as fuels for the body.  The reason for this increased attention stems from how impactful your metabolic health is on your overall heath, your life span, and your health span – the percentage of your life spent in good health.  However, if you’ve spent much time looking through articles or listening to podcasts on these topics, your head will quickly spin with all the ways people measure metabolic status.  So, let’s break down some of the most common measurements and discuss how and why we use them. 

Blood Glucose

Glucose is a simple sugar that is used for energy throughout the body.  This readily-used molecule is transported in the blood to the cells that need it, and measuring it can indicate how well your body responds to energy needs.  A fasted blood glucose level is a common way to take a snapshot of your glucose control.  While humans can function at a wide range of blood glucose levels, a healthy person will maintain a fasted glucose between 70 and 99 mg/dL.  A fasted glucose between 100 and 125 mg/dL would be in the “prediabetic” range, meaning your body is struggling to maintain healthy glucose levels, but not quite to the point of diabetes.  Importantly, this is typically a sign of insulin resistance—when insulin doesn’t work as well (especially at muscles), the body has a harder time controlling glucose. A fasted blood glucose of 126 mg/dL or greater would be considered in the “diabetic” range.1  

There are several ways to measure blood glucose.  Classically, and most accurately, it involves a blood draw and processing in a lab.  A less invasive and quicker method involves a simple finger prick and a small drop of blood in a portable measuring device.  You may have also heard about continuous glucose monitors.  These small devices are implanted just under the skin and measure glucose in the fluid between your cells – the interstitial fluid.  These devices take a glucose reading every few minutes without the pain of repeated finger pricks.  

Understanding how your glucose levels respond to various foods and activities can help paint the picture of your metabolic health.  If your blood glucose spikes with a meal and takes a long time to recover to normal range, this may indicate that your body is struggling to maintain a healthy glucose level.   

Oral Glucose Tolerance Test (OGTT)

This is a specific glucose test that determines how well your body responds to a single large dose of glucose.  If your physician thinks you might be at risk for diabetes, they might order a glucose tolerance test in which you will test baseline blood glucose levels before drinking a glucose bolus and then again 1 hour, 2 hours, and maybe 3 hours later.  Glucose is typically measured through a blood draw and a slow return to normal glucose levels will likely be cause for lifestyle and/or pharmaceutical interventions. 

Hemoglobin A1C, HbA1C, or simple “A1C”

As glucose circulates through your blood stream, some of it attaches to your red blood cells on a protein known as hemoglobin.  Because red blood cells only live for about 3 months, measuring the percent of cells that have glucose on them is a good indication of how well your blood sugar has been maintained over that timeframe.  Maintaining an A1C below 5.7% is considered normal.  5.7%-6.4% is considered the “prediabetic” range, and anything above 6.5% is grounds for diabetes.1 Measuring A1C requires a blood draw and processing in a lab.  Maintaining healthy glucose ranges consistently over time will help bring this to a healthy level. 

Insulin 

Unfortunately, we don’t have a quick way to measure insulin with a finger prick like we do glucose, so measuring it requires a blood draw.  However, insulin is an extremely important player in our metabolism and overall health.  One of the key functions of insulin is to signal cells throughout the body to take in glucose from the bloodstream.  In a healthy person, insulin is released when blood glucose is high.  This stops any lipolysis (breaking down fat to use for fuel) and works to bring blood glucose to a healthy range.  A type 1 diabetic produces little to no insulin and must, therefore, inject insulin into their body to maintain healthy blood glucose levels.  A Type 2 diabetic produces insulin, but the cells of the body have become desensitized to it.  This loss of insulin sensitivity is at the root of many chronic diseases like cancer, heart disease, Alzheimer’s disease, hypertension, low testosterone, and infertility.2  Beyond just measuring your insulin levels, here are two specific tests you might hear about when analyzing insulin. 

Homa-IR

The Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) is a tool that indirectly calculates insulin resistance.  This test was created in the 1980s and requires a blood draw to measure both fasting insulin and fasting glucose levels.3   This calculation estimates how much insulin your pancreas needs to make to control your glucose levels.  The higher your HOMA-IR score, the more insulin it takes to control your blood sugar and the more insulin resistant you are.  A HOMA-IR score of less than 1 is optimal.  Levels above 1.9 are an indication of early insulin resistance, and levels above 2.9 indicate significant insulin resistance.4,5  If you happen to have a fasting insulin and glucose measurement hanging around, you can calculate your own using the following formula6: 

fasting insulin (microU/mL) x fasting glucose (mg/dL)/405

Insulin:Glucagon Ratio

While insulin signals the uptake and use of glucose and the storage of excess energy, glucagon signals are strongest when blood glucose is low.  Glucagon signals various processes to get blood glucose levels back up.  When the ratio between insulin and glucagon is low, it is a good indication that the body has switched to using more fat for fuel compared to glucose.7  For those who fast or participate in low-carbohydrate diets regularly, this is a good measure of when you flip your metabolic fuels.

Ketones 

Ketones have received a lot of attention lately, and for a good reason.  Having elevated ketones can improve memory and learning8, reduce epilepsy9, and to protect nerves from ailments such as Alzheimer’s, Parkinson’s, and stroke.10  Ketones are a product of triglyceride (fat) breakdown.  As ketones build up in the body, it is an indication that fat metabolism is also increasing.  Therefore, measuring ketones can help you understand when you are using more fat as a fuel rather than glucose – a state known as ketosis.  There are several ketone and ketone-like substances in the body, but a very common one to measure in the blood is a molecule known as beta-hydroxybutyrate (BHB).  With a simple finger prick, anyone can measure this with a small portable device.  A measurement of 0.5 mmol/L is a common minimum threshold to be considered in ketosis.11  

Concluding Thoughts

While there are many other measurements that give us insights to metabolic health, I hope that touching on these few has helped clarify when, why, and how some of the most common tests are used.  Regardless of which analysis method is right for your circumstance, I expect you have a glimpse of how our metabolic health impacts nearly every other aspect of your life.  This should empower you to maintain healthy habits that are proven to optimize our metabolism, namely regular exercise, occasional fasting, and dietary patterns that minimize regular insulin spikes. 

References

1. https://www.cdc.gov/diabetes/basics/getting-tested.html. Accessed.
2. Bikman B. Why We Get Sick: The Hidden Epidemic at the Root of Most Chronic Disease – and How to Fight It. Dallas, TX: BenBella Books, Inc.; 2020.
3. Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC. Homeostasis Model Assessment – Insulin Resistance and Beta-Cell Function from Fasting Plasma-Glucose and Insulin Concentrations in Man. Diabetologia. 1985;28(7):412-419.
4. Antuna-Puente B, Disse E, Rabasa-Lhoret R, Laville M, Capeau J, Bastard JP. How can we measure insulin sensitivity/resistance? Diabetes Metab. 2011;37(3):179-188.
5. Gayoso-Diz P, Otero-Gonzalez A, Rodriguez-Alvarez MX, et al. Insulin resistance (HOMA-IR) cut-off values and the metabolic syndrome in a general adult population: effect of gender and age: EPIRCE cross-sectional study. Bmc Endocr Disord. 2013;13.
6. Salgado AL, Carvalho L, Oliveira AC, Santos VN, Vieira JG, Parise ER. Insulin resistance index (HOMA-IR) in the differentiation of patients with non-alcoholic fatty liver disease and healthy individuals. Arq Gastroenterol. 2010;47(2):165-169.
7. Capozzi ME, Coch RW, Koech J, et al. The Limited Role of Glucagon for Ketogenesis During Fasting or in Response to SGLT2 Inhibition. Diabetes. 2020;69(5):882-892.
8. Mattson MP, Moehl K, Ghena N, Schmaedick M, Cheng A. Intermittent metabolic switching, neuroplasticity and brain health. Nat Rev Neurosci. 2018;19(2):63-80.
9. Kang HC, Lee YM, Kim HD, Lee JS, Slama A. Safe and effective use of the ketogenic diet in children with epilepsy and mitochondrial respiratory chain complex defects. Epilepsia. 2007;48(1):82-88.
10.  Mattson MP. Energy intake and exercise as determinants of brain health and vulnerability to injury and disease. Cell Metab. 2012;16(6):706-722.
11. Deru LS, Bikman BT, Davidson LE, et al. The Effects of Exercise on beta-Hydroxybutyrate Concentrations over a 36-h Fast: A Randomized Crossover Study. Med Sci Sports Exerc. 2021;53(9):1987-1998.