Boosted metabolism. Better energy. Improved performance. That’s the promise behind influencers trying to convince athletes to use continuous glucose monitors (CGMs)—small, circular devices worn on the upper arms to get round-the-clock data on blood sugar a.k.a blood glucose levels. But how important is it for a regular cyclist to balance their glucose levels?
Originally developed to help people manage glucose dysregulation conditions such as type 1 and type 2 diabetes, these devices are becoming more widely used by those without diabetes, including athletes who track glucose levels to help with energy, eating, and exercise.
The FDA seems to agree that knowing glucose levels may help even those who don’t have diabetes, as they recently approved the marketing of an over-the-counter CGM that can be bought without a doctor’s prescription.
To get the full scope on these devices and balancing glucose levels in general, three experts explain the importance of knowing your blood sugar, the pros and cons of CGMs, and general tips for stabilizing your glucose levels without having to use a gadget.
Do you need to balance your glucose levels?
Compared to those living with diabetes, people who don’t have diabetes typically have more controlled glucose level fluctuations. However, depending on factors like food choices and physical activity, you can still experience spikes and dips, which can cause a host of unpleasant symptoms, such as brain fog, fatigue, and rapid crashes of energy, Selvi Rajagopal, M.D., assistant professor of medicine at The Johns Hopkins University School of Medicine tells Bicycling.
For those with diabetes, large glucose fluctuations can start a process of physical repercussions that can lead to illness and hospitalizations. People with diabetes have to learn to structure their eating and activity in order to keep their glucose levels in a specific zone. They also use insulin medication for this purpose, because diabetes is a disease in which the body doesn’t make enough insulin or can’t use it as well as it should, according to the Centers for Disease Control. When this happens, too much blood sugar stays in the bloodstream, which can lead to heart disease and other serious illnesses.
CGMs were created to help monitor blood glucose levels throughout the day for those living with diabetes, Alex Larson, RDN, a Minnesota-based registered dietitian nutritionist for endurance athletes tells Bicycling. In the past, people with diabetes had to prick their finger or another place on their bodies, then use a strip to measure the glucose level in that drop of blood. They would place the strip in a reader which would tell them if their blood sugar was low, in the right zone, or too high.
CGMs act differently. They are discs with a thin, disposable needle sensor that sits under the skin. The sensor measures blood sugar levels every few minutes and transfers the reading to a smartphone app or a meter which logs the results. You have to change the sensor every few days so it remains clean.
For someone with diabetes, a CGM can be life-changing, as you can monitor your blood sugar levels without having to stop whatever you’re doing and test. This is especially important for children with juvenile diabetes as their parents and school nurses can monitor them without actually having to be in the same physical space.
But these days, endurance athletes are turning to CGMs to assess how their body responds to the fuel they consume during training, Larson explains. “There are claims that using a CGM can help boost your metabolism and optimize nutrition through glucose stability,” she says.
Are there pros to using a continuous glucose monitor?
For cyclists curious about blood sugar levels, there are legitimate perks to using a CGM.
“The pros to using a CGM are that athletes gain hands-on learning in how their body responds to their training and fueling practices,” Larson says.
When used in tandem with other data, including objective metrics like heart rate and power, plus subjective measures like perceived exertion and how an athlete feels overall, CGM data can help uncover problems tied to fueling and performance, Nicole Rubenstein, MS, RD, CSSD, registered dietitian and owner of Racer’s Edge Nutrition in Colorado tells Bicycling. “For example, if four hours into a ride an athlete’s power begins to drop way below their target, you could look at blood glucose data to see if lower glucose values could be contributing to the athlete falling off pace,” she says.
Rajagopal adds there is a potential benefit for folks who notice signs of low blood sugar, such as cold sweats, brain fog, fatigue, dizziness, jitteriness, an increasing heart rate, and decreased performance during exercise. “I think in that situation, it actually can be really informative,” she says.
What are the cons of using a CGM?
The caveat is that because CGMs spit out a ton of data, there aren’t established guidelines on how to interpret this data (unless you have a glucose dysregulation disorder, like diabetes). That’s why the experts recommend consulting with a registered dietitian, primary care doctor, or endocrinologist, for advice on how to interpret and make decisions based on your CGM information.
Also, there is no current research proving that using a CGM will boost your performance, Larson says. There’s also not yet enough evidence to show that they can help diagnose over or underfueling, she adds. To boot, these contraptions are pricey: The average cost for a start-up kit is about $1,000 per year, and some CGMs can set you back several thousand per year.
Additionally, leaning too hard on CGMs could spark anxiety and an unhealthy mentality around food. Rubenstein says the devices can increase the risk of disordered eating. “I’ve seen patients obsess about clinically insignificant glucose excursions and as a result, they begin to restrict their carbohydrate intake,” she says.
This is particularly worrisome in a sport like cycling, where eating disorders are already unfortunately common. Case-in-point: One 2022 study of about 400 elite female cyclists found that 13 percent of participants had been treated for an eating disorder (ED), another 28 percent likely had an ED, and still another 32 percent likely would have benefited from getting clinically evaluated for an ED, according to their responses to a questionnaire about attitudes surrounding food. “We must be extremely careful in recommending a tool that may cause athletes to obsess over food and numbers,” Rubenstein says.
The lack of guidelines on what to do with the data can also cause people to make ill-informed decisions as a result.
“It’s very easy to overanalyze CGM data and very easy to come to the wrong conclusion,” Rubenstein says. “For example, if eating an apple causes your blood sugar to rise to 140 and eating ice cream only causes your blood sugar to rise to 120, that does not mean ice cream is a healthier choice than an apple.”
Another example: If someone who is at risk of diabetes sees that their blood sugar tends to dip quickly after consuming a gel, they may think the solution is to simply have more gels to counteract that slump. But they may benefit from swapping their gel for a more complex carb and pairing it with protein or fat. “It's not necessarily one-size-fits-all for people who have low blood sugar,” Rajagoal says. “I worry a little bit about how their management approach might change incorrectly based on information.”
The truth is, lots of things (beyond just your diet) impact glucose fluctuations, including stress, sleep habits, and exercise intensity, Rubenstein says.
To fully interpret your CGM data, you’d have to track and crunch a ton of other information. “The average person is likely not going to sit down for two hours per day to analyze all of this data,” Rubenstein says, adding she doesn’t recommend this approach even if people are inclined.
So, should you get a CGM?
All three experts agree that investing in a CGM probably isn’t worth it for the average cyclist —unless, of course, you’ve been directed to use one by your doctor. “The current literature doesn’t back up the claims and I would rather cyclists and endurance athletes focus their time, energy, and money on creating foundational fueling strategies inside and outside of their training,” Larson says.
Folks with disordered eating or a history of it, as well as those at high risk for an ED, should definitely avoid them, Rubenstein adds. The same may also be true for those with an anxiety disorder, since having around-the-clock access to glucose data “could increase anxiety,” Rubenstein notes.
If you still want to try one, Larson suggests working with a sports dietitian who can help decipher the data and provide context about the numbers, your eating, and a training plan.
How do you balance glucose level without a CGM?
The truth is, you don’t need a CGM to make smart decisions about your blood glucose levels. Larson suggests schooling yourself on general fueling guidelines for endurance sports (this is also where a registered dietitian can become useful), and testing various forms of fuel to find what works best to sustain you during your rides.
Rubenstein’s advice: Eat a well-balanced diet centered on whole foods, adequate fiber, and sufficient amounts of protein and carbs that match the intensity and volume of your training.
Also, keep in mind much of the hoopla surrounding CGMs can lead people to believe that carbs are the enemy—and they aren’t! “Our body needs carbs to use as fuel,” Larson explains. When we exercise, our bodies actually release a minimal amount of insulin after we eat carbs and sugar, since sugar can be transported directly to our muscles without the aid of insulin. Moreover, exercise raises insulin sensitivity, Larson adds. Basically, your muscles use available insulin more efficiently both during and after activity, she explains.
Last, and perhaps most importantly, know that “blood sugar fluctuations are normal,” says Rubenstein. When looking at CGM data, the aim isn’t to have a totally flat line, she explains.
Instead, the goal is for blood sugar fluctuations to be more gradual rather than rapid, which can result, in part, from eating well-balanced meals that contain a combo of carbs, proteins, and healthy fats.
The Bottom Line on Balancing Glucose Levels
Some good news for all the CGM enthusiasts: Rajagopal believes we will get to a point where we’ll have more targeted advice on CGM usage for people who do not live with diabetes, so people can use them on their own without needing guidance from a medical professional. “I think there’s a lot of potential benefit,” she says. “I just think we’re not there yet.”
In the meantime, she advises focusing on the foundational tenets of healthy eating and encourages cyclists to spend their money on a consult session with a registered dietitian, who can help them dial in a fueling plan. “At the end of it all, it’s going to come back to the basics of: How do you eat?,” Rajagopal says.
Jenny is a health and fitness journalist. She’s also an NASM-certified personal trainer. Her work has been published by Vogue, Glamour, SELF, Outside, and Health, among others. She lives in Colorado, where she teaches water aerobics at her local rec center.
