Are CGMs Banned in Olympics for Athletes without Diabetes?

Even as more athletes explore the usefulness of continuous glucose monitoring in helping them train more effectively, it appears the sensors might not be too evident in Olympic competitions in Paris.

Since 2021, at least one major sports governing body — the Union Cycliste Internationale (UCI) — has banned the use of continuous glucose monitors (CGMs) during competition for athletes who do not have diabetes. Those with diabetes may use them under medical exception rules.

But CGMs are being used by elite athletes during training and are expected to become a mainstream tool sooner rather than later, especially as two major manufacturers, Abbott Laboratories and Dexcom, received US Food and Drug Administration approval, to sell CGMs over the counter to people who don’t have diabetes. 

It’s unclear whether wearing a CGM during competition would give an athlete an edge, said Anne Peters, MD, professor of medicine at the University of Southern California Keck School of Medicine, Los Angeles. “We don’t have any research that says there’s a benefit one way or another, because it just hasn’t been done,” Peters, who is also director of USC Clinical Diabetes Programs, told Medscape Medical News. She noted that most of the CGM research has been conducted in people who have diabetes.

“Companies claim that real-time glucose tracking can help to optimize training and recovery, providing a minute-by-minute energy management system to ensure you will ‘never bonk again,'” wrote Amy-Lee M. Bowler and colleagues from Bond University and Australian University, both in Melbourne, in 2022 in the International Journal of Sport Nutrition and Exercise Metabolism.

“Whether this is a justified need, creating value to the athlete, or simply represents clever marketing of existing technology to an audience that is receptive to real-time data requires interrogation,” they wrote in their paper.

Elite marathoner Eliud Kipchoge of Kenya, who will compete for his fifth Olympic medal in Paris, has been training with an Abbott CGM at least since 2021. Abbott is intricately involved in the sport of running, as it also sponsors the six largest marathons in the world, in Tokyo, Boston, London, Berlin, Chicago, and New York City.

The company has provided sensors to Kipchoge, which have allowed the runner’s team “to build personalized nutrition plans based on glucose data in order to deliver peak athletic performance and a competitive advantage,” according to one of Kipchoge’s coaches, who was quoted in an Abbott press release.

Abbott would not comment on whether Kipchoge would be using the sensors in competition in Paris. 

It is unknown whether other athletes — even those who have diabetes — will be using CGMs at the Paris games. German tennis player Alexander Zverev — who has type 1 diabetes and won Gold in singles in the Tokyo Games in 2021 — will be competing again in Paris. 

He has reportedly been seen using a CGM in the past. Zverev also had some difficulties with officials during a French Open run in 2023 as he needed to inject insulin on court during matches. 

Insulin is considered a performance-enhancing substance, said Peters. She said she didn’t understand why Zverev would need to inject during a match, noting that there were other strategies — like “stacking insulin,” using inhaled insulin, or dosing for stress-induced hyperglycemia — that should negate the need for injections. “It seems very odd to me, but I don’t know him,” Peters said. 

Peters has worked with two-time Olympic swimmer Gary Hall, Jr, Indy Car driver Charlie Kimball, professional hockey players, and cyclists. “I’ve never had to have someone inject during a race,” she said.

For athletes who have diabetes, having a CGM or some system to ensure their glucose levels are stable is not an advantage. “It’s giving them the opportunity to just be an athlete,” said Peters.

CGMs for Endurance Athletes

Peters said it’s difficult to envision that athletes who engage in short competitions — like sprinters or many swimmers — would need to monitor glucose levels during a race. 

But there is evidence that monitoring may be important for endurance athletes. “Recent studies in free-living endurance athletes have shown that frequent episodes of hypo- and hyperglycemia are common,” wrote Mikael Flockhart and Filip J. Larsen of the Swedish School of Sport and Health Sciences in a 2023 study published in Sports Medicine.

With few studies in athletes, there’s no consensus on reference values for these competitors, they wrote. Even so, “CGMs hold promise as a tool for monitoring glucose variability, energy balance, and recovery status in endurance athletes.” The authors added that “interstitial and blood glucose levels may be an overlooked parameter in optimizing athletic performance.”

Bowler and colleagues aren’t as sure. “It is important to consider whether CGMs are sufficiently sensitive to reflect subtle changes in fueling status and exercise that have meaningful implications on athlete health and performance,” they wrote. 

They also noted some potential downsides to CGM use — including that the constant flow of information could be overwhelming, or could be triggering for people with disordered eating. And, wrote Bowler and colleagues, CGMs aren’t uniformly available to all competitors from all nations, as few countries have approved direct-to-consumer use.

UCI Medical Director Xavier Bigard told Medscape Medical News that “fairness among all riders” was one reason for instituting its 2021 ban on CGMs during competition. The Aigle, Switzerland-based sports body — which governs 203 national cycling federations — was also concerned with “maintaining the spirit of competition,” said Bigard. 

The UCI does not want to see “riders become robots remotely controlled by analyzing online biological data on their metabolic status,” he said, adding that he believes “the major usefulness of CGMs to maintain physical performances of athletes is obviously during training, in order to develop coherent energy intake plans for competitions and stabilize their metabolic status.”

Peters disagreed. Athletes are monitoring pulse, lactate levels, steps taken, and all sorts of information while training and often during competition. “You’re not turning people into robots,” she said. “If somebody is training with it and they use it to adjust their intake of carbohydrates and fluids, they should be able to wear it when they’re racing,” said Peters.

She said she still would like to see more data. “I want to see what it’s doing for nondiabetic people,” Peters said. “I want to learn if it actually helps.”

Anne L. Peters, MD, received research funding from Insulet and Abbott.

Alicia Ault is a Saint Petersburg, Florida-based freelance journalist whose work has appeared in publications including JAMA and Smithsonian.com. You can find her on X @aliciaault.