Continuous Glucose Monitoring (CGM)
Wearable sensors that provide real-time glucose data, enabling personalized nutrition insights and metabolic optimization for both diabetics and health-conscious individuals
Bottom Line
Evidence-Based Take:
CGM has revolutionized metabolic health tracking by providing real-time feedback on how food, exercise, stress, and sleep affect blood glucose. Many longevity physicians consider it one of the most valuable tools for metabolic optimization, recommending nearly every adult try it for at least a few weeks.
What the Evidence Shows:
- Individual variability: Even non-diabetics show highly variable glucose responses - ~24% spend significant time in prediabetic ranges
- Personalized insights: Same foods cause dramatically different responses in different people
- Behavior change: Real-time feedback effectively modifies eating patterns
- Subclinical detection: Can reveal metabolic dysfunction before standard tests
Honest Assessment:
CGM is a powerful biofeedback tool, but it's not something most healthy people need long-term. The recommendation: use it for 1-2 months to learn your personal glucose responses, then apply that knowledge going forward. The technology excels at showing you your specific triggers - which foods spike you, how exercise timing affects glucose, and how sleep quality impacts metabolic control.
Caution: Can promote anxiety or obsessive behavior in some individuals. Not recommended for those with eating disorder history.
Science
How CGM Works:
A small sensor inserted under the skin measures glucose in interstitial fluid (the fluid between cells). Readings are taken every 1-5 minutes and transmitted wirelessly to a smartphone app.
Key Metrics to Track:
| Metric | Optimal Target | Why It Matters |
|---|---|---|
| Mean glucose | <100 mg/dL | Lower averages correlate with better metabolic health |
| Glucose variability (SD) | <15 mg/dL | High variability linked to oxidative stress |
| Peak glucose | <140 mg/dL | Spikes cause inflammation and glycation |
| Time in range (70-140) | >90% | Standard metric for glucose control |
The Glucotype Discovery:
Research has identified distinct "glucotypes" - patterns of glucose response that vary dramatically between individuals: - Low variability: Stable glucose, minimal spikes - Moderate variability: Some meal-related spikes, quick recovery - High variability: Large swings, slow recovery, prediabetic patterns
Roughly 24% of "healthy" non-diabetics show high-variability patterns, spending ~15% of their time above prediabetic thresholds - invisible to standard fasting glucose tests.
What CGM Reveals:
- Personal food responses (rice might spike you but not bread)
- Exercise timing effects (morning vs evening workouts)
- Sleep quality impact (poor sleep = worse glucose control)
- Stress response (cortisol elevates glucose)
- Meal composition effects (protein/fat with carbs blunts spikes)
Why This Matters for Longevity:
Chronic glucose elevations and high variability are associated with: - Increased cardiovascular disease risk - Accelerated aging (glycation of proteins) - Higher inflammation markers - Greater oxidative stress - Increased dementia risk
Supporting Studies
6 peer-reviewed studies
View all studies & compare research →Practical Protocol
CGM Protocol:
Phase 1: Discovery (Weeks 1-2)
- Wear CGM continuously
- Eat your normal diet without changes
- Log all meals, exercise, sleep, and stress
- Observe patterns without judgment
Phase 2: Experimentation (Weeks 3-4)
- Test specific foods to find your triggers
- Try meal timing variations
- Test exercise timing effects
- Experiment with food combinations
Phase 3: Optimization (Ongoing)
- Apply learnings to daily life
- Periodic CGM use to verify changes
- Annual or biannual check-ins
Key Experiments to Run:
- Carb tolerance test: Try 50g carbs from different sources (rice, bread, potato, fruit)
- Meal order test: Same meal - carbs first vs protein/fat first
- Exercise timing: Same meal before vs after workout
- Sleep impact: Compare glucose after good vs poor sleep nights
- Stress response: Note glucose during stressful periods
Optimal Targets:
- Mean glucose: <100 mg/dL (aim for ~90)
- Standard deviation: <15 mg/dL (aim for ~10)
- Peak: <140 mg/dL (ideally <120)
- No readings above 140 mg/dL
Pro Tips:
- Test foods in isolation first, then in combinations
- Morning glucose responses often differ from evening
- Walking 10-15 minutes after meals significantly blunts spikes
- Protein and fat before carbs reduces glucose response
- Sleep is often the biggest lever for glucose control
Risks & Side Effects
Psychological Risks:
- Anxiety/obsession: Constant data can create unhealthy fixation
- Orthorexia trigger: May worsen disordered eating patterns
- Decision paralysis: Too much data can be overwhelming
Who Should Avoid:
- History of eating disorders
- Health anxiety prone individuals
- Those who obsess over metrics
Physical Risks (Minimal):
- Skin irritation at sensor site
- Rare allergic reactions to adhesive
- Minor bruising during insertion
Accuracy Limitations:
- Measures interstitial fluid, not blood glucose (5-15 min lag)
- Less accurate during rapid changes
- Can be affected by pressure on sensor
- First 24 hours often less accurate
Interpretation Cautions:
- Single readings less meaningful than patterns
- "Normal" glucose doesn't mean metabolically healthy
- Context matters (exercise spikes are different from food spikes)
Risk Level: Low physical risk; moderate psychological risk for anxiety-prone individuals
Who It's For
Best Candidates:
- Biohackers wanting personalized metabolic data
- Those with prediabetes or family history of diabetes
- People who've tried "everything" for weight loss
- Athletes optimizing performance nutrition
- Anyone curious about their metabolic response patterns
Good For:
- Learning your personal carb tolerance
- Optimizing meal timing and composition
- Understanding exercise-glucose relationships
- Detecting subclinical metabolic issues
- Data-driven nutrition decisions
Not Recommended For:
- Those with eating disorder history
- People prone to health anxiety
- Anyone who obsesses over numbers
- Those looking for a "magic fix" (it's a learning tool, not treatment)
Best Approach:
Short-term use (1-2 months) for education, then periodic check-ins rather than permanent wear.
How to Track Results
Key Metrics to Monitor:
| Metric | How to Track | Target |
|---|---|---|
| Average glucose | App dashboard | <100 mg/dL |
| Standard deviation | App stats | <15 mg/dL |
| Time in range (70-140) | App percentage | >90% |
| Peak readings | App alerts | <140 mg/dL |
| Post-meal spikes | Manual logging | <30 mg/dL rise |
Food Logging Protocol:
- Photo every meal
- Note time, composition, portion size
- Record glucose 1hr and 2hr post-meal
- Rate satiety and energy levels
What Good Data Looks Like:
A well-controlled 24-hour example: - Average: ~90 mg/dL - Standard deviation: 9-10 mg/dL - Peak: 102 mg/dL - Low: 77 mg/dL - Range: 25 mg/dL
Pattern Recognition:
After 2-4 weeks, you should identify: - Your worst spike triggers - Best pre-meal strategies - Optimal exercise timing - Sleep's impact on your control
When to Retest:
- After significant diet changes
- When starting new exercise program
- During stressful life periods
- Annually for metabolic check-in
Compare CGM Services:
See OptimizeBiomarkers CGM Comparison for head-to-head comparisons of Levels, Nutrisense, Signos, and more.
Top Products
CGM Services (App + Sensors + Insights):
- Levels Health - Best overall experience, comprehensive app, strong educational content, community access. Starting at $199/year + sensors.
- Nutrisense - Includes registered dietitian access, good for those wanting professional guidance. $225-350/month.
- Signos - Weight loss focused, GLP-1-like approach using glucose optimization. $199-399/month.
- Veri - Budget-friendly option, clean app interface. $99-199/month.
Direct CGM Purchase (DIY):
- Dexcom Stelo - First OTC CGM for non-diabetics, ~$99/month for 2 sensors
- Freestyle Libre 3 - Widely available, smaller sensor, 14-day wear. Requires prescription but often available via telehealth.
What to Look For:
- App quality and insights
- Sensor comfort and accuracy
- Community/support access
- Integration with other health apps
- Coaching availability (if desired)
Recommendation:
Start with Levels or Veri for the best balance of cost, app quality, and educational value. The app insights are worth more than the hardware alone.
Compare All Options:
See OptimizeBiomarkers CGM Comparison Grid for detailed head-to-head comparisons of Levels, Nutrisense, Signos, Abbott Lingo, and more.
Cost Breakdown
CGM Service Comparison:
| Service | Monthly Cost | Includes | Best For |
|---|---|---|---|
| Levels | ~$199/year + sensors | App, insights, community | Beginners, comprehensive |
| Nutrisense | $225-350/mo | Dietitian coaching | Those wanting guidance |
| Signos | $199-399/mo | Weight loss focus | Weight management |
| Veri | $99-199/mo | Basic tracking | Budget-conscious |
| Direct CGM purchase | $75-150/mo | Just sensors | DIY approach |
CGM Hardware Options:
- Dexcom G7: ~$75-100/sensor (10 days)
- Freestyle Libre 3: ~$35-75/sensor (14 days)
- Stelo (Dexcom): OTC option, ~$99/month
Cost-Effective Approach:
- Use a service like Levels for first 1-2 months (education phase)
- Switch to direct sensor purchase for periodic check-ins
- Total first-year cost: ~$400-800
Insurance/HSA:
- Not typically covered for non-diabetics
- HSA/FSA funds usually eligible
- Some services offer payment plans
Value Assessment:
CGM provides unique personalized data unavailable any other way. For metabolic optimization, the 1-2 month investment often yields insights that inform years of better decisions.
Recommended Reading
Podcasts
Transform Your Metabolic Health & Longevity by Knowing Your Unique Biology | Dr. Michael Snyder
Your glucose response to foods is highly individual - some spike to potatoes, others to grapes -...
#104 Dr. Ben Bikman: How To Reverse Insulin Resistance Through Diet, Exercise, & Sleep
Your glucose can look normal while insulin is 2-4x elevated. Covers the physical signs that...
#064 Dr. Michael Snyder on Continuous Glucose Monitoring and Deep Profiling for Personalized Medicine
About 33% of Americans are prediabetic but 90% don't know it. CGMs reveal that identical foods...
Dr. Casey Means - The Root Cause of Metabolic Dysfunction
Dr. Casey Means discusses the importance of removing processed foods and prioritizing...
Discussed in Podcasts
26 curated moments from top health podcasts. Click any timestamp to play.
Sleep deprivation drives insulin resistance
People sleeping six hours or less per night have higher fasting blood sugar levels and increased insulin resistance, leading to less fat burning and more muscle loss even when dieting.
"Those people who get six, six and a half or so less or less hours of sleep per night have higher fasting blood sugar levels. This is a problem."
Body temperature and pulse as free metabolic health indicators
Jayton Miller explains how tracking body temperature and pulse provides a free, accessible way to assess metabolic health without expensive functional medicine tests.
"Jayton talks about why you want to track your body temperature and pulse, especially when you're just getting into this. He shares his thoughts on polyunsaturated fatty acids, like omega-3, and his thoughts on cod liver oil."
Metabolism myths debunked by science
Shawn Stevenson and Prof. Tim Spector challenge common metabolism myths, explaining what actually affects metabolic rate and why popular beliefs about fast and slow metabolisms are largely wrong.
"Metabolism myths debunked"
Age and metabolism changes are not what you think
The discussion covers how metabolism changes with age, revealing that the decline is far more gradual than commonly believed and is more related to muscle loss and activity changes than aging itself.
"Age and metabolism changes"
Sleep quality is the single best predictor of daily blood glucose on a CGM
Ben Bikman notes that when wearing a CGM, sleep quality outperforms diet and exercise as the top predictor of glycemic control on any given day.
"When I've worn CGMs, I absolutely see that the single most predictive variable of my glycemia in any given day is how did I sleep?"
CGM reveals hidden glucose spikes from common foods
Different people spike from different foods. CGMs help identify your personal glucose triggers and build healthier eating habits.
"Today's episode features a self-confessed believer in the philosophy that more data is usually better, an enthusiast for all things wearable technology, including and particularly continuous glucose monitors, but also sleep trackers, fitness trackers, exposome trackers, and more. In addition, he is the chairman of the Department of Genetics and director of the Center for Genomics and Personalized Medicine at Stanford University. That man is Dr. Michael Snyder. Today, we talk a lot, including how some of these technologies, such as the more lab clinical analytic varieties like measuring metabolomics, transcriptomics, proteomics, and genomics, might change medicine for the better, making it more personal, making it more preventative. Many of you, I'm sure, will be particularly interested in our discussion in the overall utility of continuous glucose monitors, or CGMs, from a preventative medicine standpoint. While CGMs like the Dexcom and the Freestyle Libre are still considered a medical product and for the most part are prescribed under the care of a physician, they have been fairly commoditized with companies like NutriSense, January AI, and Levels, making them widely and easily available to lifestyle optimizers through a physician network, usually around a couple hundred dollars per month. In this episode, Dr. Snyder and I discuss how his genomic analysis revealed he was at risk for type 2 diabetes and how ultimately this coincided with an eventual diagnosis. How some of Dr. Snyder's data suggests that 9 out of 10 people with prediabetes are unaware they have it. This is important because even prediabetes can be clinically relevant. How a person's blood glucose response to a specific type of food can drastically differ from another person's. How Dr. Michael Snyder used wearable devices to help diagnose his Lyme disease. How Dr. Snyder's ongoing study used wearable devices to help identify elevated heart rate as one of the first symptoms in many illnesses, including COVID-19. How smartwatches that can detect heart rate variability may be able to help detect some heart conditions such as atrial fibrillation. How measuring a person's exposome can identify what airborne pathogens they've been exposed to and how Dr. Snyder is trying to determine what this means for disease risk. How children exposed to high levels of air pollution have biomarkers of Alzheimer's disease in their brains. How certain lifestyle modifications such as sauna use and sulforaphane can help rid the body of some airborne pollutants. How Dr. Snyder's data suggests that different organs such as the heart, liver, and kidneys age at different rates in different people and how this may define not only how people age at different rates, but what diseases they are more susceptible to, how the microbiome in the gut influences glucose regulation and cholesterol, and so much more. But before we jump in, I want to mention just a couple of things. If you've been enjoying our podcast, you don't want to miss out on our newsletter. I send out an email newsletter when we have a new fully researched topic page, when we have exciting new podcast episodes, or if there's been new research on some of my favorite topics. It's the best way to get curated information from me and my team on topics I think you should know about. It's also a place where I open up a little more freely than I do on social media. I'd love to have you join our email list and get our informative updates. To sign up, just head over to foundmyfitness.com forward slash newsletter. That's foundmyfitness.com forward slash N-E-W-S-L-E-T-T-E-R newsletter. One last reminder, anything discussed in this podcast is not intended in any way as qualified medical advice. If you need qualified medical advice, please seek it out. With that said, enjoy the podcast with Dr. Michael Snyder. Welcome back, everyone, to another episode of the Found My Fitness podcast. I'm super excited to be sitting here with Dr. Michael Snyder. He is the chairman of the Department of Genetics and director of the Center for Genomics and Personalized Medicine at Stanford. He runs a team of over 100 scientists at Innovation Lab at Stanford as well. Him and his collaborators are doing some really exciting research that will really change the healthcare system, shift it from one that's focused on treatment only to one that's really able to be focused on prevention in addition to treatment. He is also the founder of QBio, which is a company that gathers quite a bit of data to give people a better understanding of their health status, as well as the founder of a company called January AI, which is involved in glucose monitoring. So I'm super excited to have you here today, Mike. Thanks for having me. I kind of wanted to kick off this podcast, Mike, with a quote from William Thompson, who is a famous, he was a famous mathematician and physicist. He basically formulated the first and second laws of thermodynamics. And he's got this quote that I've often referred to, because I just think it's a great quote. And the quote is, if you can't measure it, you can't improve it. And I feel like that's so relevant to your work, and particularly even to yourself. I mean, you are probably one of the most extensively monitored humans there, there are in modern day. I mean, you've measured everything. I mean, people can't even imagine all the things you've measured on yourself. Maybe you could talk a little bit about what sort of parameters you've, you've measured in yourself and what you've learned from that data? Yeah, sure. So we're all about collecting data. I'm a believer you can't have enough data. More information is always better than less information. So what do we collect? Well, we do deep molecular measurements on me. We'll, for example, sequence first of all my DNA so I know what genes, what kinds of risk factors I might have, genetic risk factors. We also do very, very deep molecular measurements on me, meaning we'll draw my blood and urine and profile literally tens of thousands of molecules. We'll study my poop for the microbiome. And we do a lot with wearables that we'll, I'm sure, talk about today with smartwatches and other devices. In fact, I have eight of those devices I use every day. You've actually got a pretty interesting story. So you've sequenced your entire genome, and you learned some really interesting predispositions that you have. And that actually turned out to be a pretty interesting story. Sure. Yeah. No, actually, this big data collection has helped me times. And the first was in fact, from my genome sequence. So I sequenced my genome. It told me things that I was at risk for. One of them was quite surprising. It said type 2 diabetes and I'm not overweight. I exercise pretty regularly and I thought, well, you know, how can that be? I don't have a family history of type 2 diabetes, so I wasn't too sure it was right. But I was, in fact, tracking my sugar levels, which is what happens when you get type 2 diabetes. Your sugar levels go up, as well as many other things. And what we discovered, actually, about nine months into the study, after I sequenced my DNA, saw this risk for type 2 diabetes, my sugar actually was shooting up through the roof. And I was only following it closely because of the fact my genome told me I was at high risk. And in fact, when I first discovered this, I was going in getting a test for something called insulin resistance, which is associated with type 2 diabetes. And the doctor actually, you know, she was skeptical. Why are you here? You don't look like you have diabetes because I'm not overweight. You don't have family history. You know, it doesn't make any sense. And I said, well, my genome said I have this going on. And so she actually drew blood and my sugar levels were high. Actually, we were both surprised. In fact, she repeated the measurements, and sure enough, they were quite high."
Levels' 75,000-person CGM study: the largest non-diabetic glucose dataset ever
Levels ran an IRB study with 75,000 participants over 3+ years - the largest CGM dataset linking glucose to nutrition in non-diabetics.
"We've got 75,000 participants, many of whom have been using CGM for years inside this data set. And it's the largest by far of its kind ever."
The dawn effect and how menstrual cycles dramatically shift glucose response
Everyone gets a 20-30 point morning glucose spike (dawn effect). Women's glucose shifts dramatically with estrogen/progesterone cycles.
"The degree of impact of the progesterone and estrogen cycle is wild for a lot of women and it can be really frustrating."
AI-powered glucose prediction: Levels aims to replace CGM with predictive models
Levels trains AI on billions of CGM data points to predict glucose response to meals without a sensor. Still too imprecise for individuals.
"We have by far the largest data set that corresponds in a non-diabetic population CGM data with nutrition specifically and exercise."
Continuous glucose monitors for real-time metabolic health
Casey Means discusses continuous glucose monitors as a tool that tells you in real time exactly how the food you eat affects metabolic health, alongside wearables for heart rate, HRV, sleep quality, and temperature.
"And when that process is not working properly, there's this block of energy flow from the food we're eating, the two to three pounds of food we eat every single day. There's a block to that turning into an energy currency that we can use to power our lives. And just like any machine that doesn't have the power that it needs to work, it's going to be dysfunctional. You're not going to get the output you want. And that's literally the root of our chronic disease epidemic. And I think a lot of people might say, like, well, how, like, it's, it's a pretty big thing to say that, like, all these issues that we're facing that seem so different are actually rooted in the same thing."
Cgm: Benefits
set of discoveries has been repeated by other groups across the world and is gaining track and basically tells us that data coming from the host, from the human host, and data coming from the...
"It's my absolute pleasure and great talking to you, Rhonda. Thanks again to Dr. Iran Alanov for joining me all the way from Tel Aviv, Israel for our latest expert interview. And thanks to our listeners for tuning in. If you're looking to quickly learn more or dive deeper into the science on metabolism, brain aging, time-restricted eating, an analytical dissection on the best healthspan promoting practices and more, you will probably enjoy our premium podcast, The Aliquot. Each episode is short and focused on a single topic, curated and remixed from the best of our longer form videos, interviews, and members-only Q&A sessions, dozens of which are now found along with comprehensive notes right on our members dashboard. I also do monthly Q&As, which go out on the Aliquot as well. We also send out a bi-monthly science digest where we summarize science stories that I think you should know about. And there's more. These all add up to a really great membership experience and it helps me to make this podcast, including the free one, one of the best resources it can possibly be for the wider health and aging community, all while getting some cool resources that wouldn't otherwise exist. It's a good deal. You can try out the premium membership for 30 days. Find that at foundmyfitness.com forward slash trial. That's foundmyfitness.com forward slash T-R-I-A-L, trial. Thanks for listening and talk to you very soon."
And I think that's going to be really important information
And I think that's going to be really important information. And I know there's a lot of people harping on, because another study came out on CGMs provide no benefit at all to the non-diabetic.
"And it gives us insight into the types of foods and the amount of foods that we can eat. And I think that's going to be really important information. And I know there's a lot of people harping on, because another study came out on CGMs provide no benefit at all to the non-diabetic."
Who to Follow
Notable Advocates:
- Dr. Casey Means - Co-founder of Levels, metabolic health advocate
- Ben Greenfield - Uses CGM for performance optimization
- Jessie Inchauspe (Glucose Goddess) - Popularized "glucose hacks"
- Dr. Robert Lustig - Metabolic health researcher
Scientific Leaders:
- Dr. Michael Snyder (Stanford) - Led glucotype research showing individual variability
- Research showing 24% of "healthy" individuals have prediabetic patterns
The Levels Team:
Founded by Dr. Casey Means and Josh Clemente, Levels has been instrumental in bringing CGM to the wellness market and funding metabolic health research.
Synergies & Conflicts
Glucose Optimization Stack:
- CGM (monitoring)
- Time-restricted eating (meal timing)
- Walking 10k steps (post-meal walks)
- Zone 2 cardio (metabolic flexibility)
- Sleep environment (glucose control)
Metabolic Health Stack:
- CGM (data)
- Apple cider vinegar (glucose blunting)
- MCT oil (alternative fuel)
- Time-restricted eating
- 30-30-30 rule (protein-first approach)
Performance Stack:
- CGM (fueling optimization)
- Exogenous ketones (dual fuel)
- Zone 2 cardio (fat adaptation)
- Caffeine (timing with glucose)
Compare CGM Services:
- OptimizeBiomarkers CGM Comparison - Head-to-head comparisons of Levels, Nutrisense, Signos, Abbott Lingo, and more
Related Tracking Interventions:
- HRV training - Nervous system tracking
- CGM - Metabolic tracking
- Sleep tracking (Oura, Whoop) - Recovery tracking
What People Say
Why CGM Became Popular:
What Users Report:
Common Discoveries:
Criticisms:
Valid concerns - CGM is best as an educational tool, not permanent monitoring for healthy individuals.