Will Continuous Glucose Monitoring Improve My Performance?

What is a continuous glucose monitor?

Glucose, or blood sugar, is the sugar in your blood. We get glucose from food, especially carbohydrates, and it is the body’s main source of energy. Experts have known for many years that reductions in blood sugar during athletic activity are associated with performance impairment. Additionally, efforts to avoid low blood sugar during athletic training and events have been shown to improve performance and endurance (Bowler et al., 2023).

Continuous glucose monitors (CGMs) have recently entered the athletic performance sphere for their supposed ability to inform athlete’s nutrition choices. While CGMs are typically used for individuals with diabetes to monitor blood glucose and to dose insulin accordingly, the devices have recently increased in popularity among athletes who want to more closely match their fueling to changes in their blood sugar in the hopes of avoiding erratic, performance-hindering fluctuations.

Some companies market their devices with the promise of helping athletes more precisely fuel for exercise by providing minute-by-minute blood sugar readings throughout the day—before, during, and after training. With this information, athletes are supposed to know exactly when to consume carbohydrates during the day to achieve the best possible glucose stability (Perform Stronger and Recover Faster with CGM, 2023).

What are the benefits of using a CGM for athletic performance?

Because off-label (unapproved use of an approved drug) usage of CGM devices is so new, the body of research supporting their usage is limited. In a 2022 article in the International Journal of Sports and Exercise Metabolism, researchers found that athletes use CGMs as a “personal nutrition coach,” allowing them to test new methods of fueling during training and analyze how their body responds to these strategies during activity (Bowler et al., 2023).

Athletes can also use CGMs to manipulate how much carbohydrate they consume following or between training sessions in order to support recovery (Burke et al., 2018). Because individual athletes respond differently to different types of carbohydrates, CGMs can help athletes figure out what types of carbohydrates work best for them. For example, some athletes “bonk” when they rely solely on fast absorbing carbohydrates such as gummies, gels, and sports drinks because of the rapid rise and subsequent drop in blood sugar that often follows the consumption of these simple carbohydrates. Other athletes may find that those same simple carbohydrates work well for shorter, high intensity training, but for longer training and events, they need to rely on more substantial, complex carbohydrates, such as bars and starches. Using a CGM, athletes can see the results of their fueling in real time and have objective data supporting their nutrition choices rather than needing to “go by feel.”

Is there a downside to using a CGM to improve athletic performance?

The most obvious downside to the use of CGMs is the lack of evidence supporting their effectiveness. While there are many theoretical and anecdotal benefits to using a CGM—from professional and amateur athletes alike—there is no scientific consensus on whether the availability of real-time blood sugar feedback actually produces measurable performance improvements. Furthermore, some incidences of blood sugar abnormalities are normal and not directly related to a mismatch in fueling and energy usage. For example, hyperglycemia (high blood sugar) after exercise is a normal physiologic response and not the result of a faulty fueling strategy (Bowler et al., 2023). From a practical standpoint, CGMs are expensive, and availability is limited in the United States.

Having CGM data without context can also cause athletes undue stress. In more extreme cases, poorly understood blood sugar data could influence athletes to mistakenly compensate for normal episodes of hyperglycemia by withholding food or questioning what was otherwise a good nutrition plan. CGM data has the potential to allow athletes to optimize training and recovery, but this data should not override an athlete’s internal signals and other more subjective training markers such as rate of perceived exertion.

Some data suggest that other data-generating fitness wearables cause feelings of dependency and guilt for athletes (Burford et al., 2021), as well as a decrease in enjoyment and flexibility around exercise (Toner, 2018). While there is no current literature to confirm or deny this to be true with CGMs, it is reasonable to expect that users may have similar experiences with CGMs as they do with other performance-related data-generating devices.

As is always the case, devices are never a substitute for individualized care from a trained healthcare professional. Individuals wanting to experiment using CGMs for sports performance will want to consult with a trained healthcare provider in order to more fully understand the nuances of this information.