Intermittent Fasting: Can a Continuous Glucose Monitor (CGM) Help?

Intermittent fasting is a diet plan where you cycle through alternating periods of fasting and eating. Research suggests intermittent fasting (IF) might help with weight management and health issues, like prediabetes, diabetes, and heart disease. 

However, it can be hard to know if intermittent fasting is working for you. To see how their eating habits and intermittent fasting affect their bodies, some people are experimenting with using a continuous glucose monitor (CGM).

But, the truth is, there’s no good evidence that using a CGM is helpful for intermittent fasting, unless you have diabetes. There are other ways to see how intermittent fasting affects your health. Plus, having too much information about your blood sugar can make you feel anxious or lead you to make health changes that aren’t really necessary (like avoiding a certain food completely). 

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Let’s take a closer look at intermittent fasting and CGM. We’ll also talk about other ways you can monitor the health effects of intermittent fasting. 

What is intermittent fasting?

Intermittent fasting (IF) is a diet where you follow a set pattern of eating and not eating (fasting). 

There are many different intermittent fasting patterns you can follow. For example, you might eat during an 8-hour window every day, then fast during the rest of the time. Or you might eat normally 5 days a week, then fast for the other 2. 

No matter the pattern, the idea is to go long periods without food or high-calorie drinks.

How does intermittent fasting work? 

Put simply, the body has two fuel systems, similar to a hybrid vehicle. One uses carbohydrates for fuel, like putting gas in your car. The other uses stored fats, like the energy stored in an electric car’s battery. 

By not eating food or having caloric drinks for long periods — generally between 10 and 16 hours — your body begins to burn fat for energy. 

EXPERT PICKS: WHAT TO READ NEXT

• Should you use a continuous glucose monitor (CGM) if you don’t have diabetes? Probably not. Find out what four doctors have to say. 

• I have diabetes. Can I do intermittent fasting? Yes, with supervision. Learn tips on how to get started. 

• How much does a CGM cost? Find out how much a CGM costs — and whether insurance will pay for it.

Findings suggest that intermittent fasting may make a positive difference for certain health conditions, including:

• Overweight or obesity

• Metabolic issues (like diabetes, high blood pressure, and high cholesterol)

• Inflammation

• Mental health

Can a continuous glucose monitor (CGM) help with intermittent fasting?

Using a continuous glucose monitor (CGM) probably won’t help with intermittent fasting, unless you’ve been diagnosed with diabetes.

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A CGM is a wearable device that tracks your blood glucose, 24 hours a day. It’s mainly used for people with diabetes and prediabetes. But some people also use it to keep an eye on how lifestyle changes — like intermittent fasting — affect their blood glucose. And soon you won’t even need a prescription to get one. 

While there’s evidence that CGM is helpful in Type 1 and Type 2 diabetes, its use is largely hypothetical for lifestyle changes or weight loss. This means that there isn’t any solid proof that CGM is valuable during intermittent fasting. And there’s also no evidence that using a CGM can improve your health if you don’t have diabetes. 

After all, if you’re otherwise healthy, it’s unlikely that you’ll see big swings in your glucose levels, even when you’re fasting. And, even if you do get some interesting data, there aren’t any guidelines available yet on how to interpret your results. 

What metrics are helpful to track with intermittent fasting?

That depends on what your health goals are when it comes to intermittent fasting. Some of the more popular intermittent fasting metrics include tracking changes in:

• Weight

• Body fat

• Sleep

• Mood

• Exercise

• Appetite

• Energy levels

• Blood pressure

• Cholesterol

• A1C 

Keep in mind: It isn’t necessary to monitor everything — just what’s most important to you. 

How can I keep track of my fasting periods?

Keeping track of when to eat and not eat can be confusing, especially at first. That’s why tracking your fasting periods can be helpful, either on paper or with a smartphone app. While both options will be insightful, a digital tool has its perks. In addition to reminding you when to fast, many apps can track other metrics and symptoms, too — like weight, mood changes, or energy levels. And you can pick and choose which data is most helpful for you.

Using the right digital tool can also give you a 360-degree view of how intermittent fasting impacts your general health and well-being over time. 

What are the possible risks of intermittent fasting?

As mentioned above, intermittent fasting may have a wide range of health benefits, including weight management and metabolic improvements. Research also suggests intermittent fasting can be an effective nonmedical option for Type 2 diabetes. But scientists warn that more research is needed on its safety, benefits, and long-term effects. 

If you’re considering intermittent fasting, talk with a healthcare professional before getting started. According to the National Institutes of Health (NIH), fasting may be risky or even dangerous if you:

• Are age 24 or younger

• Are pregnant or breastfeeding

• Take insulin or other medications for diabetes

• Have a prescription medication that must be taken with food

• Have epilepsy

• Work the night shift

• Use heavy or dangerous machinery at work

Fasting might also increase your risk of gallstones — especially if you regularly fast for long periods. 

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Written by:

Jewels Doskicz, RN, BA

Jewels Doskicz, RN, BA, is an Arizona-based registered nurse with 22 years of hospital-wide clinical nursing experience and 11 years of medical writing and editing experience. She was a former healthcare content creator for a digital health tool at HealthLoop and director of clinical content operations at GetWellNetwork.

Edited by:

Sophie Vergnaud, MD

Sophie Vergnaud, MD, is the Senior Medical Director for GoodRx Health. An experienced and dedicated pulmonologist and hospitalist, she spent a decade practicing and teaching clinical medicine at academic hospitals throughout London before transitioning to a career in health education and health technology.

Reviewed by:

Sarah Gupta, MD

Sarah Gupta, MD, is a licensed physician with a special interest in mental health, sex and gender, eating disorders, and the human microbiome. She is currently board certified by the American Board of Psychiatry and Neurology.

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