A month ago, I decided to try wearing a Continuous Glucose Monitor to check my blood glucose levels, despite not suffering from any health condition.

I thought I was going to have great blood glucose. I mean, I’m a pretty healthy guy, I take care of myself, I pay attention to what I eat, I exercise. Imagine my surprise when I realized that some “healthy” foods I have been eating were actually destroying my blood glucose and that the situation was not as good as I had expected!

In the first few paragraphs of this article, you’ll find some basic information about CGM. If you want to skip that part and go straight to what I discovered, go “The Experiment” section.

Keep in mind that the insights I discovered are individual. What works for me might not work for you, and you might find different results. The value lies in personal research!

Let’s dive in!

Why did I wear a CGM?

You can’t be passive if you want to be healthy. Good health is not something that just happens. For me, health requires mindful practice, not too crazy, that prevents future problems.

I started being interested in tracking health data a few years ago. First, I started tracking some basics: calories, heath beat, daily activity. I realized that the most important thing for optimizing your health is to obtain as accurate data as possible. To get better, you need to know where you stand and what is it exactly you’ll need to work on.

My reasons for doing this experiment:

1. I was curious to see my blood glucose levels, especially after I realized how important they are for overall health and longevity.
2. I have a history of type 2 diabetes in my family.
3. I wanted to see my body’s response to particular foods and understand whether there’s a specific food that is damaging my health.
4. General curiosity about health optimization and technology!

How does it work?

A CGM consists of a plastic patch attached to a tiny metal needle with a chip inside connected to a Bluetooth reader or your smartphone. It’s a minimally invasive device that gives you your blood glucose levels throughout the day. You can read your levels on an app.

How to get one?

It depends on where you live. In the US, you need a prescription from your doctor to get a CGM. In Europe, you can buy one over the counter. So for me, it was not a problem. I could order CGMs just like any other item.

Which CGM to chose?

There are two options you can choose from:

• Dexcom G6
• Abbott Freestyle Libre 2

They have some minor differences, but they’re similar if you don’t care about the details.

I went for the Freestyle Libre 2, as it was the cheaper (around 50€ for 14 days) and more readily available for me!

Is it comfortable to wear?

You don’t need any help with inserting a CGM. You can do it yourself. It takes about 2 mins, and it’s super easy! Check out this video to understand how to do it.

I didn’t experience any discomfort while wearing a CGM. Once you get used to it, you even forget you have one, and it wasn’t a problem to exercise regularly with it.

The Experiment

For my experiment, I followed the framework: track, understand, act.There are two things you’ll need to track. First, you have to remember to log the data every 8 hours as the Freestyle Libre can store up to 8 hours of blood glucose readings. To log the data, you just take your phone and put it against the CGM. Second, you need to keep a record of the food you eat so you can use it for the ‘act’ part (I used MyfitnessPal for the detailed tracking & Awesome Meal Tracker for the timestamps).

I did extensive research to understand what are the optimal blood glucose levels. It’s complicated to get reliable information since the optimization of blood glucose for non-diabetics is an underdeveloped area of research. I also read about other people’s experiences to understand how I can keep my blood glucose from skyrocketing.

As I was uncovering what foods were causing my blood glucose to increase drastically, I started to act. I started eliminating and adding foods, as well as experimenting with some ways to mitigate the increases.

My insights for the “understand” part

As I said, it’s hard to determine what are the optimal glucose ranges. Researchers haven’t really reached a consensus on what metrics you should look at.

Here are some parameters you should consider:

• Fasting blood glucose
• Pre-meal levels
• Post-meal peak
• Average glucose
• Standard deviation

When it comes to metabolism, people are classified into three categories: healthy, pre-diabetic, and type 2 diabetic. This is likely to change soon since researchers are showing that these categories fail to grasp the major differences within each category.

The official “healthy ranges” for blood glucose levels are:

• Fasting blood glucose:
• Pre-meal levels: 72–90 mg/dL
• Post-meal peak:
• Mean 24 hours glucose: 90–105 mg/dL

Many research papers suggest these values are not the optimal values. For example, this paper suggests fasting blood glucose above 85 mg/dL is associated with a higher mortality rate from cardiovascular diseases.

Once I knew what the numbers were to aim for, I was ready to start my experiment with a CGM!

My Findings

Food-related learnings

In the first part of this CGM article series, I wrote about how studies have shown that there is high inter-person variability in blood glucose levels for the same food. In other words, the majority of nutrition advice has limited value until you confirm they work for you.

I discovered that some food that is considered healthy might be bad for blood glucose, while not really being indispensable for overall health or irreplaceable by other foods. It’s about compromise: when you understand that your blood glucose reacts badly to some healthy food, you can always find alternatives with similar nutrients or try to mitigate the bad effects!

The first day I wore CGM was right after I did a 40-hour fast. To break my fast, I prepared “healthy” oatmeal & banana pancakes. My blood glucose went from 90 mg/dL to 200mg/dL in 30 minutes! I usually eat big portions (150+g of carbohydrates), but I would never expect this sharp increase in such a small period of time. I found a possible explanation for this in this paper that suggests that a short-term low carbohydrate diet (and fasting means no carbohydrates) increases post-meal glucose spike after larger carbohydrates meal. Takeaway: if you practice fasting, you should be careful about breaking fast with carbohydrates meal!

Generally, I was disconcerted when I realized how bad my body responded to some “healthy foods”.

For example, bananas & oats are considered healthy foods, but having a spike to 180+ mg/dL isn’t going to do good for you. Here are some other foods that might skyrocket your blood glucose:

• A bowl of 200g of berries can spike my blood glucose levels to 150+ mg/dL in less than 30 minutes.
• A “balanced breakfast” — crushed nuts, chia seeds, an apple & a few dates (healthy right?), spiked my girlfriend’s blood glucose to 210 mg/dL.

• As expected, pastries aren’t great for you :) Here’s her response to eating two pastries on a fasted state:

Takeaway: be careful when eating some of the healthy fruits! You’re not going to stop eating them, but there might be things you could do to lower the negative effects for your blood glucose (check the section below). Also, of course, you should reduce sugar and refined carbs as much as possible!

I also found that wearing a CGM and understanding how some unhealthy food affected me was a really powerful deterrent. You’ll think twice before eating some unhealthy food when you understand just how unhealthy it is!

In the first weeks, I was constantly surprised by what I saw. Could it be just me? I don’t think so. My girlfriend did the experiment with me, and she also had unexpected findings. After doing some research, I found many testimonials going in the same direction (here, and here, for example, andthis research paper).

I grew up eating a lot of carbs. I always thought it’s completely fine as long as you exercise and you don’t put on weight. I was wrong. After a big portion of carbs, my blood glucose levels skyrocket (above 150 mg/dL, and most of the time even higher).

Healthy individuals rarely wear CGMs, so it left me thinking a lot. Am I the problem, or is it a widespread invisible situation?

I found this great Ted Talk by Dr. Peter Attia, in which he suggests there might be a problem in our dealing with metabolic problems.

Fasting-related learnings

I’m a big fan of fasting. My fasting routine is every day 20:4 fast (short eating window of four hours); longer fasts on Mondays(40-hours fast); 72 hours fast every three months.

It’s widely accepted that fasting is great at reducing blood glucose levels. I can confirm this! While fasting, my blood glucose was in the range between 80 and 90 mg/dL. However, I had a problem that after fasting, my blood glucose levels would be extremely sensitive. After 40 hours of fasting, I tried breaking my fast with a limited amount of carbohydrates (around 50g) and still saw a significant glucose response. After the increase, it stayed elevated for 24 hours.

Food strategies I tried for optimizing my blood glucose levels

When I saw how badly my blood glucose was reacting to some foods, I searched for ways to mitigate the bad effects. Here’s what I found I could do:

• Eat the fat source first! For the same meal, the order in which you eat the food will impact your blood glucose levels. Having the fat source first will help blunt the post-meal spike.
• Eat slower! This was a big challenge for me, I’m a really fast eater. Unfortunately for me, eating fast has a bad impact on blood glucose levels. I tried to eat slower (not always successfully), and I saw some positive effects.
• Use cinnamon! Using freshly ground Ceylon cinnamon can help decrease blood glucose levels. I tried putting some in my coffee. It seems to be working, but I’ll have to try longer.
• Increase fiber intake! I tried using more ground flaxseed as an additional source of fiber. I can’t directly isolate the effect of it, but again it seems to have positive effects on my blood glucose levels.

There are many more strategies you can explore, but the approach is the same: track, understand, act. The era of trying health/lifestyle changes without having reliable feedback to assess their impacts has to end!

How exercise impacts blood glucose?

I was curious to see how exercise impacted my blood glucose levels. My intuition led me to think that exercising lowers blood glucose levels. Again, I was wrong.

High-intensity exercise and weight training increased my blood glucose levels up to 150 mg/dL. Research shows that this type of training is not bad for you in the long-term, but it does increase your blood glucose since it stresses your body. You should also take some other parameters into consideration. For example, the pre-workout meal or lack thereof can affect how much your blood glucose increases during and after a workout.

Low-intensity exercise, like walking, has a lowering effect on blood glucose. I saw that going for a walk after eating helped reduce the post-meal spikes.

Athletes will likely want to monitor their blood glucose levels to time their exercise and nutrition for the most optimal outcomes.

The impressive effect of meditation

I started meditating on and off a few years ago. I always felt it had a great effect on my overall wellbeing. I would feel better, but I could hardly explain why (except for the obvious calming effects for the mind). Then I got a CGM!

One day I was stressed and decided to meditate for 15 minutes. Before starting the meditation, my blood glucose level was 120mg/dL. After 15 minutes of meditation, I checked again, and it was 95mg/dL!

I couldn’t believe it, so I tried again on other days. I saw the same pattern.

If before I needed extra motivation to make meditation part of my everyday life, now I got it!

What about sleep and blood glucose levels?

Is there a direct link between sleep quality and blood glucose levels? It’s not very easy to tell, but there are definitely some patterns I did notice.

Eating just before going to sleep isn’t optimal. When I did so, my blood glucose levels would stay elevated during a good part of the night, and my “readiness” score would be really bad on the following morning. Even worse than that is to eat a large amount of carbohydrates before sleeping.

Generally speaking, going to sleep at least 3 hours after the last meal was optimal for me. It can be hard for social life, but during this time in quarantine, it wasn’t a problem!

Another interesting thing I noticed was that a blood glucose spike in the early morning. This is called the “Dawn phenomenon” and it’s linked to the body’s release of cortisol. I didn’t manage to improve this yet, but I noticed that it’s highly correlated to morning stress levels.

Conclusion of my experiment

Overall I’m extremely happy with this experiment. The lack of precision and personalization in nutrition and health is something that bothers me a lot, and that I want to change. I think that every single individual could gain powerful information by wearing a CGM. It’s time for people to figure out what really works for them. It’s time for us to overcome the “Nutri-religion” and focus on personalized prevention!

I got used to wearing a CGM and I’m obtaining valuable and direct feedback from it. It may sound far-fetched to some people, but now I wouldn’t want to go back to not using it.

The only hard part of this experiment is that you can’t fool yourself. Sometimes the blood glucose readings will show a non-significant high value and that’s ok. However, if you see a pattern that is far from optimal (which was my case) you can’t unsee it. You have to face it, especially since you can do something about it! It can be hard at first, especially if you thought you were going to see great levels. It’s what I call the “Longevity Paradox”. To optimize your healthspan and your longevity, you will have to face some “bad news” to avoid facing worst later on.

It kills the mood to see your blood glucose levels go to 210 mg/dL after a meal that you love. But, if you’re serious about health and longevity you will want the honest truth rather than the convenient dismissal.

Next steps

It’s been a year that I’m working on a project to help people optimize their metabolism. I think the widespread use of CGM devices will have a major impact on solving the global metabolic crisis. Many voices in the field are saying this. I was convinced they were right, and after seeing it with my eyes, I can’t unsee it.

The future of metabolic health is to help people to optimize their metabolism before the burden of chronic diseases arises.

For that to happen, people will need help, guidance, and programs.

That’s what I’m building with my co-founder! It started as our personal passion for longevity and prevention and soon it will be ready to help you too to optimize your metabolic health.