What Your Blood Sugar Is Really Telling You: A Guide to Continuous Glucose Monitoring

Why a 2-4 week CGM trial might be the best investment you make in understanding your metabolic health—and the metrics that matter most.

If you have diabetes, struggle with weight, deal with PCOS, or simply want to understand how your body responds to food—a continuous glucose monitor (CGM) might be one of the most eye-opening tools you’ll ever use.

I recommend that my patients try a CGM for at least 2-4 weeks. That’s enough time to see your patterns, identify problem foods, and gain real awareness of your metabolic health. The insights are often worth far more than the cost of the device.

But here’s what most people get wrong: they focus on the wrong numbers.

Stop Obsessing Over the Spike

When people first start using a CGM, they tend to fixate on that peak number after eating. “My glucose hit 160! Is that bad?”

The peak matters—but what matters more is how long it stays elevated.

Here’s the key insight: A spike that resolves in one hour is far less concerning than one that lingers for three hours.

In healthy individuals, blood sugar typically peaks about 30 minutes after eating and returns to baseline within 2 hours. If you’re seeing prolonged elevations—glucose staying high for 3+ hours after a meal—that’s a signal worth paying attention to. Those extended excursions are linked to increased cardiovascular risk and metabolic dysfunction.

So when you look at your CGM data, ask yourself: How quickly does my glucose come back down? That’s often more informative than the peak itself.

The Most Important Number: Time in Range

If there’s one metric to focus on, it’s time in range (TIR)—the percentage of your day spent within your target glucose zone.

International consensus guidelines have established clear targets, and they’re more achievable than you might think.

If You Have Diabetes

Your target range is 70-180 mg/dL. Here’s what to aim for:

• Time in range: More than 70% of the day (about 17 hours)

• Time below 70 mg/dL: Less than 4% (about 1 hour)

• Time above 180 mg/dL: Less than 25% (about 6 hours)

• Time above 250 mg/dL: Less than 5%

Here’s what’s powerful about these targets: hitting 70% time in range correlates with an HbA1c of about 7%. And every 5% improvement in your time in range translates to meaningful reductions in diabetes complications. Small, consistent gains add up.

If You Don’t Have Diabetes

For metabolic health optimization, use a tighter range of 70-140 mg/dL.

Research on healthy individuals shows they typically spend about 96% of their time in this range. A reasonable goal for someone without diabetes is 90% or higher. If you’re consistently below that, it’s worth investigating why—and it may be a signal to get screened for prediabetes.

What Your Nights Reveal

One of the most underappreciated aspects of CGM data is what happens while you sleep.

In a healthy person, glucose levels should gradually decrease overnight. But certain conditions disrupt this pattern:

Sleep apnea and breathing disorders: Research shows that people with moderate to severe sleep apnea actually see their glucose rise after falling asleep—the opposite of what should happen. The intermittent oxygen drops trigger stress hormones that raise blood sugar. If your overnight glucose looks like a slow uphill climb instead of a gentle decline, it might be worth getting evaluated for sleep-disordered breathing.

Late-night eating: Eating close to bedtime—especially carbohydrate-heavy snacks—can keep glucose elevated throughout the night. This sustained elevation contributes to inflammation and disrupts sleep quality. Your body needs that overnight period of lower glucose to recover and repair.

If you’re waking up tired despite getting enough hours of sleep, your overnight glucose pattern might hold clues.

The Blood Sugar-Heart Connection You Should Know About

Here’s something I find fascinating and increasingly relevant: the relationship between blood sugar and heart rate variability (HRV).

HRV measures the variation in time between heartbeats. Higher HRV generally indicates better cardiovascular health and stress resilience. Lower HRV is associated with increased disease risk.

Research from the Framingham Heart Study and others has shown that HRV decreases as blood sugar rises—even in people without diabetes. And in people with diabetes, chronically elevated glucose is associated with significantly reduced HRV.

What does this mean practically? If you’re tracking HRV with a wearable device and seeing consistently low numbers, dysregulated blood sugar might be part of the picture. And improving your glucose control may help improve your HRV—and with it, your overall cardiovascular health.

This is an emerging area, but the connection is strong enough that I think anyone serious about metabolic health should be aware of it.

A Note for Those with PCOS

If you have polycystic ovary syndrome, pay special attention to your glucose patterns.

Up to 95% of women with PCOS have some degree of insulin resistance—even those at a normal weight. And CGM studies have revealed that women with PCOS show abnormal postprandial patterns even when their oral glucose tolerance tests come back “normal.” Specifically, their glucose takes longer to peak and longer to come back down.

This matters because insulin resistance is both a driver and a consequence of PCOS. High insulin stimulates the ovaries to produce more androgens, which worsen symptoms and further impair insulin sensitivity—a vicious cycle.

A CGM can help you identify which foods and eating patterns keep your glucose more stable—and that stability can translate into better hormone balance, more regular cycles, and reduced symptoms.

How to Actually Use This Information

Once you have CGM data, here’s how to make it actionable:

1. Look at duration, not just peaks. A meal that spikes you to 150 but comes down in an hour is likely fine. A meal that takes you to 140 but keeps you there for 3 hours is more problematic.

2. Calculate your time in range. Most CGM apps do this automatically. If you have diabetes, aim for >70% at 70-180 mg/dL. Without diabetes, aim for >90% at 70-140 mg/dL.

3. Check your overnight pattern. Is glucose trending down as it should, or staying flat or rising? A problematic overnight pattern is worth investigating.

4. Experiment systematically. Test one variable at a time—meal composition, meal timing, pre-meal walks, sleep timing—and see what moves the needle for you.

5. Don’t chase perfection. Even healthy people spend some time outside their target range. The goal is consistent improvement, not obsession.

The Bottom Line

A continuous glucose monitor gives you a window into your metabolism that no other tool can provide. It shows you how your body responds to food, stress, sleep, and exercise—in real time, across days and weeks.

For people with diabetes, it’s becoming standard of care. For those with PCOS, obesity, or metabolic concerns, it’s a powerful diagnostic and motivational tool. And for anyone curious about optimizing their health, even a short trial can be genuinely illuminating.

Focus on time in range. Pay attention to how long your spikes last. Look at your nights. And remember that small, consistent improvements compound over time.

The data is there. The question is what you’ll do with it.

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Questions about CGM or how to interpret your data? Leave a comment below or reply to this email—I read everything.

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