I recently spent about 6 weeks wearing a continuous glucose monitor (CGM). I learned more about how my body worked in these 6 weeks than in the other 40 years living in this body, including all the hours spent studying biochemistry, physiology, and nutritional science. I also got lots of questions about the CGM. I am going to start with the questions and then dive into the highlights of what I learned. If you don’t have questions, skip on down!

Common Questions

What is a continuous glucose monitor? This is a thing you stick on the back of your arm that has a little microneedle that sits under your skin and monitors the levels of glucose in your blood. You’ve likely seen them on the arms of people with type 1 diabetes. It connects to an app on your phone that gives you data about your glucose levels every minute of the day. I got mine from NutriSense, so it connected to their app. NutriSense also provided access to a registered dietitian trained in interpreting the results and providing advice accordingly.

Did it hurt? No. Seriously, not at all. It took me an embarrassingly long time to put the first one on. I do NOT do well with needles. But this was a non-event. I also never felt the needle while I was wearing it. Pulling off the monitor hurt worse than putting it on. That adhesive is strong.

Why did I do it? A couple of reasons. Primarily, I was curious. I talk a lot about glucose, but I didn’t really know what my own glucose was doing in response to food, exercise, or stress. So, I wanted to understand glucose more personally, less academically. Also, I spend a lot of time working on a study in which all the participants have type 2 diabetes. I have no idea what it’s like to constantly monitor your blood sugar or think about what everything you eat or drink will do to your glucose and, therefore, your chronic health condition. What I did does not come close to walking in those shoes, but I do have a little better understanding of the glucose-monitoring piece of that experience.

What’s “normal” glucose? There are different ways to measure glucose levels and insulin sensitivity (i.e., whether insulin and insulin receptors are working properly to get rid of the high glucose).

Fasting. You may be familiar with fasting blood glucose. Standard guidelines say 100 mg/dL is normal fasting glucose, but some argue that you want to be closer to 90 mg/dL. But most of your day is not spent fasting. When you eat, it goes up and then down again.
Random: Throughout the day, anything above 200mg/dL is considered very high (if you didn’t JUST eat, that probably means you have diabetes). Anything below 70 mg/dL is considered too low (hypoglycemic) for many people, but that may vary between people.
Post-meal: Another important measure is postprandial glucose, which is your glucose level 2-3 hours after a meal. The goal is to return to pre-meal levels 2-3 hours after the meal. Ideally, this is 70mg/dL-100mg/dL.
Area under the curve (AUC): After you eat, you’ll have more sugar in your blood. That’s how eating works. You want to aim to keep that below 140mg/dL and you want to get back to normal quickly. The area under the curve tells you how much glucose exposure your body had during the 2 hours after you ate. The goal here is 25 or less.
Time within range: This is the percentage of time that your blood glucose is within your target range of 70mg/dL-140mg/dL (140 being the highest you want to get after a meal). Goal here is 100%.

What did I learn?

I could write multiple posts on all of these. But here I am going to hit on the top 9 things I learned. Why 9? Because that’s where I ended up, and I wasn’t going to throw in something forced to even it out. If you want a refresher on why glucose matters, you can check out these posts (here or here) or this post from Levels.

1. Carbs need clothes — they do bad things when they are naked

I’ve known, academically, that having a high-carb meal, snack, or drink can spike your blood sugar. I also know, academically, that you have less of a spike if you eat protein and fats with that meal or drink. I also know from personal experience that I feel sluggish and also super hungry after meals or snacks that are mostly carbs, which I know, (again, academically) means that there was a big glucose response I am recovering from. But oh, how different it was to see it!

When wearing a CGM, you can see the spikes from glucose, and the steeper the hill, the faster glucose entered your blood. When you eat pure sugar, it goes straight up! That means sugar just flooded into your bloodstream and your body is scrambling to do something with it. The goal is to have more gentle slopes so that your body has time to deal with the glucose as it enters your blood over a longer period.

I did two experiments in which I ate snacks of pure fruit: one was a plate of fruit, the other was just a banana. The response was crazy. My glucose went way up in both. The solo banana was a more normal snack amount of food. My blood sugar went from 85 mg/dL to 139 mg/dL, and I still wasn’t totally recovered hours later. You can see the chart to the left.

BUT I did a similar experiment another time but with some cheese first. And I had a far less severe response. It still went up, but not nearly so crazy.

Why? Well, if the only thing in your gut is carbs (or almost the only thing in your gut), then the enzymes that break it down into simple sugars (glucose and fructose) can work really fast! Even though bananas and other fruits and vegetables have more complex carbs that take some time to break down, they are still mostly carbs that will eventually be sugar. When those enzymes have nothing else to do and can easily get to all those carbs to break them down, the process happens quickly. I didn’t try cokes or fruit juice; I imagine that would be a much steeper cliff because those drinks are full of a lot of simpler sugar that already is or becomes glucose very easily.

The takeaway: If you love to snack on fruit (or other high-carb snack or drink), pair it with something high in protein and fat. Nuts, peanut butter, and cheese are good options. It blunts the spike!

2. The Order of Food/Drink Matters

The exact same food can affect your glucose differently based on the order you eat it. According to Jessie Inchauspe, a biochemist, author of Glucose Revolution, and aka @glucosegoddess on IG, the ideal order is: vegetables, followed by proteins and fats second, and starches and sugars last. It was legit! I don’t really want to eat my asparagus while the rest of my meal gets cold. But a pre-dinner was a super easy way to test this out. And it worked! I had a much more mellow response to pasta when I ate a salad first. Even without prioritizing the veggies, dessert at the end of the meal produces a tamer glucose response than a piece of bread at the beginning. One night I had some crème brûlée after a long (super fun) dinner with some friends. Nothing happened to my glucose at all! Nothing! It was a big meal with lots of proteins, fats, and wine (more on that last item later).

Why? This is similar to the idea behind naked carbs. If you eat starches and sugar last, your gut is already full of a lot of other stuff and the enzymes are giving their attention to what is already there. The same enzymes that break down starches and sugars in the bloodstream are busy with those vegetables. And even if you aren’t eating it in exactly the same order, some cobbler after a plate of barbeque and collards is going to have a much smaller impact than if you ate that cobbler first! There is a bunch of other stuff in your gut, which slows down the enzymes’ ability to break up the sugar so that glucose can be absorbed. Because it takes longer to break down these sugars and get them into your bloodstream, there is far less of a glucose spike.

The Takeaway: Eat dessert last and very close to the end of your meal while your belly is full of protein and fats. Try a salad before your dinner or have a savory appetizer before the bread course.

Bonus Takeaway: Your glucose may respond better to a dessert than a high-carb snack.

3. Post-Meal Walks are Like a Miracle Drug

Taking a walk after dinner seems like one of those things our grandparents did. One of those wholesome activities that feels almost nostalgic. OMG, our grandparents were onto something. I found that I could eat a meal that I knew might spike my glucose, and then go take a 15-minute walk and be totally in the clear. That dinner that ended with crème brûlée was followed by a long walk home from the restaurant. Was it the order I ate the food or the walk? Hard to tell. But I learned that with my normal eating patterns and habits, I could completely avoid going over 130 mg/dL all day simply by taking a walk after lunch and dinner. (Note: a lower-carb dietary pattern works well for me and my blood glucose exists on the low end of normal. So, as the pharma ads say, “results may not be typical”).

Why? I am going to do a whole post on glucose and exercise, so I’ll keep it brief here. When you eat a meal with any carbs, glucose enters your blood. Your cells take in whatever glucose they need to use for energy and whatever they can store as glycogen. Your liver takes care of the rest, but it can take some time for the liver to process all of that extra glucose into other things like fat and cholesterol. So your glucose stays high. BUT if you take a walk, suddenly more cells need that glucose for energy—your muscles, your heart, all the things involved in walking. So the glucose in your blood has a lot more places to go and is immediately used for fuel!

The Takeaway: This is just one more reason to get up from your desk and get some fresh air after lunch and go take that evening walk! Even if you don’t care about your glucose, I bet it will also have some other benefits.

4. Cheers to Wine!

I love red wine. I’m also a pretty big fan of rosé, which is still very in season (in my opinion) because it’s still pretty warm in Texas. I have a glass or 2 of wine most nights. I actually drank less while wearing the CGM so that I could experiment more. Alcohol skewed all results. It was shocking to me how much alcohol blunted my glucose spikes. Pasta, rice, and even bread were no match against a couple of glasses of pinot. I could cut the delta (the change between the moment you eat and the peak) by almost half by drinking wine with my meal.

You know that awesome meal I keep mentioning with the crème brûlée? We also had a lot of red wine. And we ate for hours. So, some combination of these things means I finished the meal with a glucose level that would be considered normal if I weren’t eating anything at all. This was not a well-controlled experiment (it’s an inherent problem in nutritional science). Don’t worry, I tested the wine theory a lot, and it was a consistent result. Cheers to science.

Why? I don’t know. I mean I have a vague idea, but not enough to write it up and send it out into the blogosphere. I know that there are a number of properties of alcohol (maybe this one included) that have led many scientists to conclude that moderate amounts of alcohol have an important role in a healthy dietary pattern, like the Mediterranean diet pattern. I also know that wine can be really dangerous for people with diabetes because of its hypoglycemic effect (i.e., because it lowers blood sugar). I also know that for some people, it delays the spike, so they end up with higher glucose in the middle of the night when their body needs to be resting not dealing with a bunch of sugar. Proceed with caution with this one! I also did not experiment with other non-wine alcohols. I assume liquor and beer would have similar results, but I’m out of my depth here.

The Takeaway: If you do not have diabetes or prediabetes, a little wine with dinner may be good for your blood sugar. But I am not putting it on my recommendation list for everyone.

5. Bread Hates Me

I don’t regularly eat sandwiches. They always make me feel sluggish and super hungry within a couple of hours. I do far better with eggs or leftovers for lunch, even a hearty salad. But sometimes a sandwich is the best or only option, so I was curious to see what it did to my blood sugar. It was terrible! I did it a few times, and I spiked at least 50 points every time. When I ate other bread, it was less extreme than the response to sandwich bread. I had avocado toast on Easy Tiger sourdough a few times (with a full avocado and eggs) and I also ate bread at restaurants without this result. But was it all the fats, proteins, and (when at a restaurant) wine? Or was it the difference between handmade bread vs. ultra-processed bread? I didn’t isolate them to find out. But I can tell you I feel different afterward, and that is enough for me.

Why? Bread has a lot of carbs, and even the whole wheat kind of bread breaks down into a lot of glucose. More processed carby food are designed to break down into sugar faster than the less processed versions, including the ones advertised as healthy. Many breads also have sugar added to them. Sandwich bread was really the only ultra-processed carbs I ate during this experiment, and I had them outside my house, so I never saw what the ingredients were. So, who knows? And who knows if I would react this way to other ultra-processed carbs or sandwich breads that are less processed. Who knows if you would. We are all different. But if you feel tired and/or super hungry within a couple of hours of eating a sandwich, you may have a similar response to bread. If not, maybe not.

The Takeaway: If there is a food you eat that makes you sluggish and starving shortly afterward, that may be because it is inducing a glucose spike. There are plenty of other food options, and you don’t have to feel that way!

6. Stress Spikes Glucose

Stress plays a huge role in your glucose regulation. Since I stopped practicing law full time, I have had way less stress in my life - both chronic and acute. But don’t worry, there were a couple of stressful moments while I was wearing the CGM, so I got to see stress in action. In the first instance, I was eating a sandwich at the nutritional science back-to-school event when I learned that I was going to be teaching my own class starting in less than a week for the first time ever. Panic. Glucose almost hit 200 (sandwich + stress=glucose chaos). Then I got to see it bump again when I stood up in front of that class for the first time a few days later.

Why? When you are stressed, your body releases cortisol (among other things), triggering the fight or flight response. Your body starts preparing you to run from a lion or fight a bear or whatever very physical activity that it thinks may be imminent. Part of this process involves dumping glucose (from glycogen) into your bloodstream. The problem is that most of the time you are experiencing stress, you are neither fighting nor fleeing. There are usually no lions or bears. You don’t need all that glucose in your blood.

The Takeaway: Managing stress is as important to your glucose regulation as managing your food intake. Also, do you see how stressing over your food intake is physiologically counter-productive? At least when it comes to your glucose levels.

7. Hard Exercise also Spikes Glucose

I run 4-5 mornings a week. On Wednesdays, I do a workout (think track work or repeated runs up a hill) and Saturdays I run long. The other days are shorter, slow miles. I almost never eat before a run. Yet, every single run raised my glucose. The short, easy runs gave me a small little bump. On the long runs, my glucose crept up higher and higher as the run went on. A sip of Gatorade would send it through the roof. I did one 12ish mile run completely fasted and still got up into the 130s. Wednesdays were nuts. I would show up to the run completely fasted, and a hard workout sent me north of 160 multiple times! Eating a little something beforehand or even just taking an electrolyte pill before I ran would blunt the run-induced spike, but nothing kept it completely flat.

Why? This is so cool that I plan to write an entire post on it. But briefly, that run-induced spike is from glycogen. Your body is responding to you in flight mode by emptying your stored glucose into your blood so that you have the energy you need. Because you are exercising, this does not trigger the normal insulin response that a glucose spike does because all the doors to your muscle cells are wide open simply because you are exercising. Remember that they normally require insulin to open their doors. Why did eating change this? Because the glucose from my pre-run banana had reached my bloodstream before I started running hard, so my body wasn’t quite as panicked about making sure that I had the glucose to do what I needed.

The Takeaway: There’s no real takeaway here. It’s just pretty cool.

8. CGMs May be the Closest Thing We Have to Precision Nutrition — But It’s Not Perfect

Nutrition is hard. It can be a daunting task to figure out what foods or eating patterns work best for your unique lifestyle, genetics, epigenetics, and gut microbiome. Some people can thrive on a vegan diet, others are so dysregulated without meat that they stop mensurating. Some people can eat dairy, but most of the world lacks the enzyme to break down lactose. In some people, Splenda causes their glucose to spike because of what their gut bacteria do with that artificial sugar. Two people can endure the same stressful situation and have completely different physiological responses. In fact, you could experience the same two stressful events on two different days with two different responses. How the heck is anyone supposed to figure any of this out?! The CGM, supported by an app with good UX and a dietician or health coach is probably the closest thing we have to help people figure out some of it.

Why? With a CGM, you can learn about how your blood glucose and glucose metabolism respond to foods you eat, the time you eat them, the stress you experience, the activities you do, and the sleep you get. Dysregulated glucose metabolism is the precursor to most chronic diseases, so this is a pretty big deal. Getting this piece right, could be life-changing for millions of people.

The Takeaway: Understanding your body’s response to glucose is huge. I don’t want to understate how key this could be for so many people. However, it is not the end all be all. A glucose monitor isn’t going to give you a genetic, enzymatic, or microbiome profile. It also isn’t even going to tell you about the amount of insulin that your pancreas is pumping out in order to take care of that glucose. Years before your glucose levels indicate that you have a glucose metabolism problem, your pancreas works overtime to pump out insulin so that your glucose stays in check. This period of high insulin (hyperinsulinemia) could be a really important time to stop the progression of metabolic disorders, but the technology isn’t quite there to be able to hold that data in the palm of your hand. YET

9. Who Could Benefit from a CGM

Who could benefit? Everyone. I am going to make a small caveat for those who struggle with eating disorders, especially orthorexia (an unhealthy focus on eating healthy food). Candidly, I found myself pulled in that direction a bit. It felt like a game to keep my glucose between 60-120 all day. I forced experiments to break that, plus there is little to learn in perfection! What would I share with you if I kept it between the lines every day? If you know you have tendencies that would put you in an unhealthy place by having that much data about everything you did, maybe skip this.

For everyone else, I could not recommend it more. If you have a number of health issues that you think are connected and your doctors are ignoring, your glucose metabolism may be the link. If you have something no doctor can diagnose, this may give you the answers. If you are trying to figure out how to eat to lower your cholesterol, lose some weight, feel less tired mid-afternoon, or sleep better, this may be the shortcut to those answers. And if not, I can almost guarantee you’ll learn something about yourself that will be worth the cost of knowing. I sound like I am being paid to advertise. I swear I am not. But here’s a link to the best commercially available CGMs I know of on the market: NutriSense and Levels.

What my glucose monitor taught me