Continuous glucose monitors (CGMs) have moved from clinics into training logs and group chats. For some endurance athletes—especially those with Type 1 diabetes, Type 2 diabetes, or prediabetes—a CGM can be a powerful tool. For others, it adds noise. The key is knowing when a CGM will genuinely help, how to use the data without overreacting, and when you’re better off sticking with a simple, practiced plan.
Who benefits most
- Type 1 diabetes
- Strong use case if you already train with a CGM. Trend arrows support small, timely adjustments in long sessions and races. Patterns across workouts guide future fueling and pacing decisions.
- Type 2 diabetes or prediabetes
- Often useful when combined with a training log. CGM trends can highlight how pre‑workout meals, fueling intervals, and pacing changes affect your stability and comfort.
- No diabetes
- Evidence for performance is mixed. If you’re curious, treat CGM use as a short, focused experiment to learn a few actionable insights, then put the device away.
What a CGM can do (and what it can’t)
- Can do
- Reveal patterns: where you tend to dip late in long runs, surge after big, infrequent feeds, or wobble in heat and high stress
- Help you time smaller, steadier fueling and adjust textures when your stomach tightens
- Build confidence that your plan keeps you in a comfortable, repeatable zone
- Can’t do
- Replace a fueling or hydration plan
- Run the race for you—pacing and mindset still matter most
- Eliminate the need to practice; data without rehearsal just creates more questions
How to use a CGM in training (simple, practical)
- Capture context, not just numbers
- Pair CGM screenshots with a few quick notes: what and when you ate, fueling intervals, session type and intensity, heat/altitude, how your stomach felt, and any stress or poor sleep.
- Look for repeatable patterns
- Scan 3–5 similar sessions. Do you dip late in long runs? Spike after a large feed? Feel “spiky” when you go out too fast? Patterns—not single spikes—drive useful changes.
- Adjust one variable at a time
- Change only timing, portion size, or product texture (softer vs. solid). Keep everything else the same for a couple of sessions. If the change helps twice, keep it; if not, roll it back.
- Build a short “data block”
- Over 2–4 weeks, plan a few key sessions (long run/ride, tempo, brick). Practice your race‑like fueling and hydration. Use CGM to confirm whether your plan produces steady, comfortable trends that match how you feel.
Simple race‑day approach (if you trained with a CGM)
- Wear it only if you practiced with it
- Race day is not the day for new tech. Use the same device placement, settings, and check‑in rhythm you used in training.
- Watch trends and arrows—then keep decisions small
- If you trend lower: use a small, fast‑acting carbohydrate you tested; keep moving calmly; reassess in a few minutes.
- If you feel “spiky,” anxious, or overly full: pause feeding briefly, sip water, ease effort for a minute, then return to your steady rhythm.
- Stick to your plan
- The CGM is there to confirm your routine, not to invite major mid‑race changes. The best decisions are the ones you’ve already rehearsed.
Common pitfalls to avoid
- Chasing single numbers
- One reading can be delayed or misleading. Reacting aggressively to a single blip often creates bigger problems than it solves.
- Changing everything at once
- Abandoning your plan mid‑session based on one spike/dip usually backfires. Make micro‑adjustments you’ve already practiced and give them time to work.
- Ignoring how you feel
- Perceived effort, breathing, stomach comfort, and pacing are still your most important inputs. If data and body cues conflict, slow down briefly, breathe, and make the smallest helpful adjustment.
- Using a CGM without a plan
- A device won’t fix a lack of routine. Start with a simple plan—then use the CGM to validate and fine‑tune it.
Using a CGM as a short learning experiment (for athletes without diabetes)
- Define your goal
- For example: learn how breakfast timing affects early runs; discover whether smaller, more frequent feeds feel better; or test if certain products sit better at race pace.
- Choose your sessions
- Pick 3–5 key workouts (long runs/rides, a brick, a tempo). Don’t wear the device all month—focus and finish.
- Take simple notes
- Meals, timing, fueling intervals, intensity, conditions, and stomach comfort. Capture a couple of CGM screenshots at consistent points (mid‑session, late session).
- Extract 2–3 insights
- Keep only what clearly helps (e.g., earlier, smaller feeds; a gentler product; a specific pre‑run meal timing). Then stop using the device and apply what you learned.
When a CGM may not be helpful
- If frequent readings increase anxiety or lead to constant tinkering
- Some athletes perform better when they lock in a practiced plan and use basic body cues to guide small adjustments.
- If you already have strong, steady routines and feel great
- Technology is optional. If your plan is working and you’re progressing, there’s no requirement to add more data.
- If you tend to outsource decisions to the device
- Remember: CGM supports your judgment; it doesn’t replace it. Your job is to stay calm, consistent, and present.
Mindset: data as a teammate, not a boss
Think of your continuous glucose monitor as a teammate who offers useful feedback after you’ve built a solid game plan. You set the strategy through practice. The CGM helps you spot patterns and confirm that your routines are doing what you expect. On race day, your best choices will feel familiar—steady fueling, steady sipping, steady pacing, and steady headspace.
Bottom line
A continuous glucose monitor can be a game‑changer for athletes who need it for health reasons and a smart add‑on for others running a focused learning experiment. If you use one, pair the data with context, look for patterns across sessions, and change only one variable at a time. On race day, trust the routines you’ve practiced and use the CGM for small, calm adjustments—not big, reactive swings. If you choose not to use a CGM, you can still perform at a very high level by rehearsing a simple fueling and hydration plan until it becomes second nature.
Dive deeper into this topic on the Nuanced Nutrition Podcast.
