March 05, 2024

Top Line

Data from the National Health and Nutrition Examination Survey (NHANES) 2009–2016 revealed that around 27.3 million Americans met the criteria for optimal metabolic health. This means that the other 290+ million people at the time this data was collected did not meet the criteria for optimal metabolic health.1

Why it Matters

Metabolic health is described in the literature as having low risk for developing cardiometabolic diseases. Metabolic syndrome is what occurs when multiple risk factors such as high blood pressure, obesity, high cholesterol (high LDL and low HDL) and triglycerides, and high fasting glucose levels are present. All of which put an individual at direct risk for developing a myriad of diseases including cancer, type 2 diabetes, cardiovascular disease, and more. 1 As a result, an individual is considered to be metabolically healthy when they have less than three of the five criteria present.

Additionally, in regard to the ongoing covid-19 pandemic having just one of the five risk factors for metabolic syndrome puts an individual at an increased risk for developing severe illness from the virus that causes covid-19. 2 Unfortunately, as stated previously, almost 90% of Americans meet at least one of the five risk factors for developing metabolic syndrome. 1

Key Takeaways

  • One should routinely pay attention to the aforementioned criteria and strive to stay within optimal levels by assessing their metabolic health.
  • Adhering to a consistent sleep, nutrition, and exercise plan that is specific to you will serve as a key preventative measure against developing metabolic disease while also improving or preserving metabolic health.
  • You need to have three out of the five criteria to be diagnosed with metabolic syndrome. Having just one out of the five is reason enough to become proactive about reducing your risk for developing metabolic syndrome.

Classifying Metabolic Syndrome

The National Cholesterol Education Program/Adult Treatment Panel III (NCEP/ATP III) provides criteria for the diagnosis of metabolic syndrome shown below. 3

  • Waist circumference of more than 102 cm in men or more than 88 cm in women
  • Fasting triglyceride level of 150 mg/dL or higher
  • Blood pressure level of 130/85 mm Hg or higher
  • High-density lipoprotein cholesterol (HDL-C) level of less than 40 mg/dL in men or less than 50 mg/dL in women
  • Fasting glucose level of 110 mg/dL or higher (which has been changed to 100 mg/dL to reflect revised criteria for impaired fasting glucose [IFG])

For an individual to be diagnosed with metabolic syndrome they must have at least three out of the five listed criteria. However, the above levels for each marker are debatable depending on who your doctor is and what levels they feel are significant or not. For example, the American Heart Association (AHA) considers blood pressure that is over 120-129 systolic and less than 80 diastolic to be elevated which is far below what is listed in the above criteria for metabolic syndrome. Conversely, going off what the NCEP/ATP III guideline means blood pressure would classify the individual as being in stage 1 hypertension according to the AHA. See image below for a full list of blood pressure categories.

Therefore, if your doctor goes by the NCEP/ATP III criteria for blood pressure and you are considered as having an elevated blood pressure by the AHA then your doctor might be prematurely disregarding a significant risk factor instead of taking preventative action. Consequently, it becomes important to be familiarized with all the different guidelines and understand how they might or might not affect you.

For an across the board look at the other various classifications for the above metabolic syndrome criteria from the likes of the World Health Organization (WHO), American Association of Clinical Endocrinologists (AACE), and International Diabetes Federation (IDF) click here.

Assessing Metabolic Health

There are many ways you can be proactive about your health and assess where you stand. In today’s day and age technology is providing us with a host of apps and equipment that let us more readily assess things like our metabolic health.

Ideally, the first step is to have fasted Blood work drawn by your doctor. A full lipid and metabolic blood panel will show you everything you need to see to assess whether or not you meet some or all of the metabolic risk factor criteria. Moreover, if you are unable to get blood work done through a doctor you can use companies like ThorneWellnessFX, or Quest Diagnostics, just to name a few.

Another way that is less direct than blood work but becoming more readily accessible is doing a cardiorespiratory test, also known as a VO2max test. In order to fully understand why this is an important test and how it assesses your metabolic health let’s briefly review the physiological mechanisms at play in body during the test.

Understanding the Mechanism

A VO2max test is essentially measuring how well your muscles take in and utilize oxygen to supply the working muscles with energy. Thus, a number of cellular reactions occur in the muscles to make this happen and the byproducts of these reactions are measured during the test.

First, let’s understand that during metabolism our body uses fat, glucose, and carbohydrates as fuel. These energy sources are given a value that is called a respiratory quotient (RQ) which lets us know which energy pathway and fuel source is being utilized at rest and during exercise.

  • Fat has an RQ of 0.7
  • Protein has an RQ of 0.8
  • Carbohydrates has an RQ of 1.0

In addition to that our muscles are comprised of mitochondria which power everything and fibers known as Type I and Type II (Type II also has IIa and IIb). However, for simplicity I am just going to refer to them as Type I and Type II muscle fibers. Type I are our slow twitch fibers that will utilize fat as a fuel source and the mitochondria to oxidize fat as energy in the presence of oxygen to power the muscle. Type II muscle fibers primarily utilize carbohydrates (glucose) as a fuel source and do not require oxygen and have a low count of mitochondria. Additionally, the oxidation of carbohydrates produces higher amounts of lactic acid in the muscle.

Interestingly, recent research has shown that lactate still forms even in the presence of oxygen just not in the mitochondria but in the cytosol of the cell instead. This is relevant because the mitochondria also use lactate as fuel creating a connection between the glycolytic pathway (Type II, utilize carbs for energy) and the aerobic pathway (Type I, oxygen and fat) referred to as the lactate shuttle theory.

During exercise our body is using a mix of fat and carbohydrates which is dictated by the types of muscle fibers being used which is dictated by the intensity of the activity being performed. When performing a VO2max test your body will switch from the Type I muscle fibers which are recruited during submaximal exercise and daily activities to Type II muscle fibers which are recruited as the intensity of an exercise increases and more effort is required.

This physiological response during exercise is measured in a VO2max test as the respiratory exchange rate (RER). The RER is the ratio between the amount of carbon dioxide exhaled and oxygen used which reveals what type of fuel is being used by the muscles during exercise. At rest, a healthy individual should be below an RER of 1.0 (0.7 specifically) which means they are primarily utilizing fat as fuel. Conversely, a metabolically unhealthy individual may have an RER closer to 1.0 or higher which signals that that individual is primarily burning glucose (carbs) at rest.

Bringing it all together, the measurements during this test like the RER reveal the types of muscle fibers being recruited, at what stage of the test they are being recruited, and what type of fuel the body is utilizing. Moreover, the end result of the test will show the final RER and then the individuals overall aerobic capacity which is quantified into a number. This number is normalized based on your sex and weight shown as milliliters (ml) of oxygen per minute (measured through your breathing during exercise), per kilogram (kg) of body weight. This number is then compared to a normative chart based on your sex and age and then classified based on where you land on the chart.

*Minimum Level of Aerobic Capacity for reduced risk of morbidity and mortality in ml/kg/min.

VO2 Max and Metabolic Health

In addition to the aforementioned criteria, metabolic syndrome patients are characterized by a decreased capacity to oxidize fats and by quickly transitioning from fat to carbohydrate oxidation during exercise. 3 Additionally, these patients will have a higher blood lactate concentration not only as exercise increases but at rest as well, a condition termed ‘metabolic inflexibility’. 3

Therefore, because both lactate and fatty acids are mitochondrial substrates, it is believed that measurements of lactate and fat oxidation rate during exercise provide an indirect method to assess metabolic flexibility and oxidative capacity across individuals of widely different metabolic capabilities. 3

Lastly, a growing body of epidemiological and clinical evidence demonstrates not only that cardiorespiratory fitness (CRF) is a potentially stronger predictor of mortality than established risk factors such as smoking, hypertension, high cholesterol, and type 2 diabetes mellitus, but that the addition of CRF to traditional risk factors significantly improves the reclassification of risk for adverse outcomes. 4 Consequently, assessing CRF through VO2max testing has become a strong predictor of mortality and is the most accurate and standardized quantification of CRF. 4

Alternative Ways to Test Metabolic Health

While the VO2max is a valid and reliable way to assess your metabolic health, it may not be practical for everyone. As a result, a more relaxed testing method like the resting metabolic rate (RMR), lactic acid finger prick test, Ketone breathe analyzer, and constant glucose monitoring (CGM) may be more suitable.

The RMR tests has a similar set up to the VO2max test where you are wearing a mask with a hose attached to it with the other end of that hose attached to a metabolic cart. You simply lay down and breathe normally through that hose for roughly 20 minutes while the metabolic cart measures your gas exchange and RER in real time. A higher RER at rest is an early warning sign and risk factor for metabolic syndrome. As stated previously, at rest you should have an RER of 0.7 indicating you are burning fat and not glucose. Burning glucose at rest means that your mitochondria are not functioning properly, and the body is relying on glucose more than fat which in turn leads to a higher amount of resting lactic acid, inflammation, and so on. It is recommended to be at least four hours fasted before taking this test.

Another way to indirectly assess your metabolic health is to prick your finger and use a device like the Lactate Plus which will measure the amount of lactate in your blood. At rest your lactate levels should be between 1.0 and 2.0 millimole. Going back to the lactate shuttle theory your mitochondria will utilize lactate as fuel. If your mitochondria are dysfunctional then metabolic health declines and your mitochondria have lost some of that ability to take in fatty acids and lactate. As a result, your blood will contain a higher resting lactate level.

The ketone breathe analyzer like the Biosense Ketone analyzer will reveal when you are in a fat burning state by measuring ketones in your breath. When you eat less carbohydrates, your liver will break down fat cells that results in the release of ketones into the blood stream for the body to utilize for energy. The key here is less carbohydrates in the diet forcing the body to breakdown fat. In a metabolically unhealthy individual this process is rather difficult even when eating less carbohydrates initially, and the body will not achieve ketosis or go into a very low state of ketosis compared to someone who is metabolically healthy. Therefore, using a ketone breathe analyzer may be a quick and reliable way to indirectly assess your metabolic health.

Finally, there is the constant glucose monitoring (CGM) from a company like Levels Health. The use of a CGM device is typically reserved for Type 1 and Type 2 diabetic individuals. This is a necessary and life saving device for diabetic individuals to help constantly monitor their glucose levels and their body’s response to the foods they are eating. A physician’s order is required to get a CGM but companies like Levels Health allow you to sign up for their product and be reviewed by a physician in your state to gain access to a CGM. This allows non-diabetic individuals to gain access to a CGM device and monitor their metabolic health and become proactive about it before things get out of hand.

Constant glucose monitoring has been gaining ground as a preventive tool for those who are not diabetic. If you recall from the beginning of this article, one of the five criteria for metabolic syndrome is having an elevated fasting glucose level of 110 mg/dL or higher. However, it is important to note that this may vary from person to person and genetics and lifestyle heavily factor into this. Thus, using a CGM in non-diabetics helps bring more awareness to how glucose levels and variability within the body affect overall health. For a deeper dive into CGM and how it can benefit you and assess your metabolic health check out the many educational blogs written by Levels.

The Final Word

Assessing your metabolic health is becoming easier and easier to do with any of the test and devices discussed in this article. However, it is important to note that the data and insights gained from these tests are like steppingstones that you are placing into the larger context of your overall health. As a result, it best to use several of these tests in conjunction with one another to help put the pieces together in accordance with your lifestyle.

For example, getting your fasted blood work done and then performing a VO2max test to assess your CRF and then following that up with the use of a CGM device for a month. This will allow you to know where you stand metabolically with the blood work and VO2max test and where you need to improve. While the use of the CGM will allow you to gain insights on how your lifestyle is either hindering, improving, or just maintaining your metabolic health. As a result, you can take immediate action day after day based on your CGM data.

The bottom line is that you can and should use all of these tests in unison with one another to help paint a more in-depth picture of your metabolic health. In addition to factoring in your lifestyle and behavioral habits to help guide you on the road to improved metabolic awareness, health, and lifestyle choices.

Jon Esposito MA, CSCS, CISSN, USAW


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