Blood Glucose Tracking for Athletic Fueling

You know how some runners hit a wall mid-marathon? Or how a strength athlete can feel fine one minute and crash the next? That isn't just bad luck or overtraining. More often than not, it boils down to one thing: blood glucose.

 

Athletes of all levels are turning to Continuous Glucose Monitors (CGMs) to decode their performance dips and energy surges. It might sound like overkill if you're not diabetic, but the logic is simple. If you could see your fuel gauge during every workout, wouldn’t you want to? CGMs, like those from Dexcom and Supersapiens, allow athletes to do just that. Real-time glucose data is becoming the secret weapon for runners, cyclists, lifters, and even CrossFitters trying to fine-tune their fueling.

 

At its core, glucose is your body’s preferred energy source during exercise. Think of it like the high-octane gas your car needs when you're flooring it. Your body taps into this reserve rapidly—especially in intense or extended workouts—and when it runs out, you’re toast. The result? A bonk, a crash, a sudden wave of fatigue that doesn’t care how motivated you are.

 

Without glucose tracking, you're essentially flying blind. Some days you feel great, others you drag through your sets, and you chalk it up to stress or bad sleep. But what if the real culprit is that bowl of cereal you ate too late? Or the fact that your post-workout recovery shake spiked your insulin and tanked your energy an hour later?

 

CGMs work by measuring glucose levels in the interstitial fluid—the stuff between your cells. There’s about a 10-15 minute lag compared to blood glucose, which is crucial during high-intensity efforts. They send data to your phone, smartwatch, or a dedicated app, showing minute-by-minute trends. That banana you ate before your run? You’ll see how quickly it spiked your glucose, and how long it took to crash. You’ll also know if your fasted workout caused a dangerous dip.

 

Using a CGM during training can reveal surprising trends. For example, endurance athletes often see gradual glucose declines, while high-intensity interval workouts can trigger spikes due to stress hormones like cortisol. Strength training is more complex. It can raise glucose modestly, but if you're glycogen-depleted, your levels might flatline.

 

Then there’s insulin. It’s the hormone that helps shuttle glucose into your muscles. Mistiming insulin—whether from food or stress—can lead to poor performance. Athletes with high insulin sensitivity might benefit from carb loading 30–60 minutes before a session. Others might do better fueling during the workout to keep glucose stable. There’s no one-size-fits-all. That’s the whole point of real-time tracking.

 

Carb timing isn’t just nutritionist folklore either. In a 2020 study by Jeukendrup et al. (University of Birmingham), endurance cyclists who consumed carbs every 20 minutes showed 8% better performance over a 90-minute ride than those who ate only at the start. That study used traditional glucose measures, but newer research with CGM-enabled athletes is showing similar benefits, especially in precision fueling strategies.

 

Pro teams are catching on. Team INEOS, the elite cycling team behind multiple Tour de France wins, reportedly integrated CGM into their training and recovery protocols. Marathon world record holder Eliud Kipchoge is rumored to use blood sugar data to plan his carb intake during races. This isn’t just tech for tech’s sake—it’s performance insurance.

 

But here’s the human side. Tracking your body that closely can mess with your head. Athletes can become overly obsessed with keeping glucose “in range,” even when small fluctuations are normal. Some report anxiety, compulsive checking, or dietary restrictions based solely on glucose spikes. The irony? Stress about the numbers can raise glucose, defeating the purpose.

 

Critics argue CGMs weren’t designed for non-diabetics, and the FDA has issued warnings against relying solely on them for medical decisions. A 2023 meta-analysis in Sports Medicine (n=276 participants, 14 trials) concluded that while CGMs can improve awareness and performance in endurance contexts, the benefit is highly individualized and often dependent on data literacy and coaching support. There’s also a cost barrier. A typical CGM subscription runs \$150–\$300 a month, putting it out of reach for many.

 

Still, the science is gaining ground. A 2022 study from the University of Colorado involving 38 trained endurance athletes showed that those who used CGMs to fine-tune carb timing improved time-to-exhaustion by 9% over 12 weeks compared to a control group. That’s not a minor edge. That’s winning vs. just finishing.

 

If you’re curious about trying it, start with a 14-day trial. Wear the CGM through your regular training, and log meals, workouts, sleep, and how you felt. Identify patterns. Did oatmeal before lifting cause a crash? Did late-night snacking mess with morning runs? Use the data, don’t let it use you.

 

There are drawbacks. CGM sensors can be finicky. Sweat, temperature, and compression can affect accuracy. Some users experience skin irritation or sensor adhesion problems. Others misinterpret short-term spikes, cutting healthy foods out of their diet. Like any tool, it requires education and restraint.

 

But beyond all the charts and numbers, this isn’t just about data. It’s about performance with purpose. It’s about giving your body what it needs, when it needs it. It’s about making smarter fueling decisions that aren’t guesswork. And maybe, just maybe, it’s about beating your last best time, not by training harder, but by fueling smarter.

 

Because at the end of the day, data doesn’t win races. You do. The tech just helps clear the fog.

 

Disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider before starting any new dietary, supplement, or fitness regimen, especially if using medical devices such as CGMs.