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The Top Mistakes People Make When Wearing a CGM

by: Michelle Sirmons MS, RDN, CSSD  |  November 21, 2023

A continuous glucose monitor (CGM) is a device that can be worn to measure your blood sugar all day. It can be an incredible tool in personalizing your nutrition and preventing metabolic disease. At Being Functional Nutrition we work with a wide variety of clients to optimize their health at every level, including using a CGM. Although wearing a CGM is helpful in understanding how your body responds to different foods, it is also important to know that your glucose is impacted by many factors outside of what you eat. One of the biggest mistakes I see in people wearing a CGM is that they only focus on how food impacts glucose levels, while not realizing the impact of lifestyle. When seeking to optimize your glucose it is crucial to consider the impact of the following:

  • Stress
  • Sleep
  • Feeding Window
  • Gut Health 
  • Nutrient Deficiencies


The Impact of Stress on Glucose

Stress is a normal part of life, but too much stress can have negative effects. Our stress hormone, cortisol, has a wide range of functions in the body. It interacts with most of our major organ functions, including the regulation of blood sugar. When the body perceives a potential threat, cortisol is released and this increases a process called gluconeogenesis, which causes glucose to flood the bloodstream. In stressful situations this “fight or flight” response fuels us with energy allowing us to be hypervigilent and quick on our feet. Blood sugar imbalances arise when you are chronically stressed because they cause constant glucose fluctuations.  Furthermore, prolonged periods of stress reduce insulin release, making it harder to control blood sugar levels.  The same meal can elicit a very different glycemic response just from being consumed when the individual is under a lot of stress. I have personally seen as much as a 20-point difference in the rise of glucose from a normally glycemic-friendly meal due to that person’s stress levels.

The Impact of Sleep on Glucose

Poor quality sleep, or short sleep durations, are major drivers of glucose fluctuations. In fact, short sleep duration has a direct correlation with insulin resistance. One study even identified how a single night of poor sleep can cause significantly higher levels of insulin resistance. Poor sleep increases inflammatory markers, such as C-reactive protein, which has been associated with prediabetes.  In addition to higher insulin resistance, poor sleep increases stress levels the following day, which -- as you have already read -- further creates a glycemic rollercoaster. The combination of poor sleep and high stress is a recipe for a glycemic disaster!

The Impact of Your Feeding Window on Glucose

There are multiple factors that can influence how you utilize glucose at night, such as your feeding window. Eating too late at night elevates glucose levels late into the evening and throughout the night as our bodies are less insulin-sensitive at night. This means we don’t process glucose as efficiently.  Additionally, your body has to prioritize digestion, when it should be getting ready for sleep and recovery.

Remember, if your body can’t fully recover at night then you may have higher stress levels the next day. Inactivity in the evening also leads to more glucose sitting around in your blood with nowhere to go. Shortening your feeding window - let's say, by eating last at 7PM as opposed to 9PM - will give your body more time to fast between meals.  This can help your body become more sensitive to insulin over time and allow time for your body to prepare for recovery, rather than digestion. Yet, with anything, 

The Impact of Gut Health on Glucose

Many people don’t realize that there is a direct correlation between gut health and metabolic health, such as blood sugar. The beneficial microbes in your gut ferment dietary fiber and resistant starches into short-chain fatty acids, which are considered one of the most important overall gut markers. Short-chain fatty acids support your intestinal barrier function and modulate anti-inflammatory activities in the gut.  In particular, the short-chain fatty acid, butyrate, plays a role in the secretion of glucagon-like peptide (GLP-1), which is considered to have anti-diabetic effects on blood sugar levels. Therefore, if your gut bacteria is imbalanced, it can have a profound effect on how your body responds to carbohydrates. Low levels of butyrate can be problematic for maintaining balanced glucose levels.

The Impact of Nutrient Deficiencies on Glucose

There are numerous vitamins and minerals involved in blood sugar regulation. A deficiency in one, or multiple nutrients, can impact your ability to use glucose efficiently. For example, vitamin D deficiencies may alter insulin responses. In type 2 diabetic subjects, researchers discovered improvements in glucose stability when supplementing with vitamin D.

Magnesium is another key nutrient that can support glucose regulation and reduce insulin resistance. In fact, magnesium supplementation has been shown to lower baseline fasting glucose levels. In pregnancy, deficiencies in magnesium increase hyperglycemia and the risk of gestational diabetes. Although there are many other nutrients involved in glucose regulation, these are two deficiencies I commonly see in our practice. You can learn more about nutrient deficiency testing here.


It is clear that factors, beyond just what you eat, impact how you respond to carbohydrates and your baseline glucose levels. Reflecting on your lifestyle habits is a helpful tool when you are struggling to maintain optimal glucose levels. Begin by improving your sleep and assessing stress management techniques. You can also play with your feeding window by adjusting the amount of time you are fasting and the timeframe for your meals. Additionally, testing for nutrient deficiencies and imbalances in the gut can further evaluate the root cause of your glucose imbalances. Looking for some more help in identifying the root cause of why your glucose is out of range? Consider working with one of our Functional Medicine Dietitians!

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