October 1, 2022 Author: Matthew Renze

What can we learn about our diet and exercise from measuring our blood glucose?

When your blood glucose levels rise, your insulin levels rise in response. Insulin tells your body to store excess glucose as fat. As a result, you gain weight.

So, keeping blood glucose levels low and stable helps you to manage your weight – as well as prevent a variety of metabolic disorders.

I typically eat a low-carb (mostly) ketogenic diet with intermittent fasting and daily exercise. So, being able to monitor and analyze my blood glucose levels is quite valuable to me for optimizing my health.

Last year, I purchased a continuous glucose monitor (CGM) from NutriSense to better understand how various foods, exercises, and habits impact my blood glucose levels.

It’s a sensor that you attach to your arm and connects wirelessly to your smartphone. It continuously reads your interstitial glucose levels every 15 minutes — all day long for up to 14 days per sensor.

Interstitial glucose levels are not exactly the same as your blood glucose levels. However, they act as a reasonable proxy for one another.

Typically, these sensors are only available to individuals with medically diagnosed diabetes. However, they are sometimes used for research and to help people improve their diet and exercise – like me.

So, to help you better understand the relationship between diet, exercise, and blood glucose, below are the top insights I’ve learned from wearing a CGM for three months.


Sugars are simple carbohydrates that are quickly converted to glucose in your body. Consuming most sugars causes a sharp spike in blood glucose followed by a sharp drop. The rapid rise and fall in blood sugar leads to feeling hungry and craving more sugars – thus perpetuation a vicious cycle of craving.

As I expected, eating foods high in sugars caused large spikes in my blood glucose. Removing sugars from my diet caused my blood glucose levels to remain low and stable after each meal. In addition, after several days without any sugars, I don’t seem to crave them at all.

However, like most people, I enjoy a sweet snack every now and then. So, I changed from eating snacks made with sugars to those that use a natural sugar substitute like allulose, erythritol, or stevia. It gives snacks the same sweet taste without the spike in blood sugar.


Complex carbohydrates, like sugars, also break down into glucose in the body. This causes a rapid rise and fall in blood glucose – but not as steep as quick sugars, though. However, complex carbohydrates also contain fiber which does not get broken down into glucose or increase blood glucose levels.

As I expected, minimizing processed carbohydrates reduced my overall blood glucose levels and kept them stable throughout the day. Eating foods high in fiber but low in other carbohydrates did not cause my levels to rise after meals. This is why it’s important to focus on net carbs (i.e. total carbs minus fiber and sugar alcohols).

As a result, I’ve replaced many of the high-carb foods that I used to eat in favor of those with low net carbs. I now avoid high-carb bread, pasta, corn, potatoes, etc., and prefer broccoli, spinach, asparagus, cauliflower, etc. There are even low-net-carb tortillas, cookie dough, and ice cream if you need a snack.


Normally, eating protein shouldn’t cause your blood glucose levels to rise. However, your body has the ability to convert excess protein into glucose through a process known as gluconeogenesis.  So, if you consume too much protein, you will see a large gradual rise in blood glucose followed by a slow decline.

As I expected, eating moderate amounts of protein did not cause any large swings in my blood glucose levels. However, binging on steak, chicken, or other proteins, did cause large rises and declines over several hours. A protein-heavy dinner would typically peak around 3 AM and cause me to be restless.

As a result, I’ve been conscious not to eat too much protein in one sitting. I prefer a moderate amount as a component of my meal rather than the centerpiece of my meal. In addition, I try to choose healthy proteins (e.g. salmon, eggs, shellfish, etc.) without any added or hidden carbohydrates or sugars.


Despite popular belief, consuming dietary fat does not make you fat. Many fats are a normal part of a healthy diet that has, unfortunately, been vilified by some outdated science and the for-profit food industry. In addition, consuming fats should not (in theory) cause your blood glucose levels to rise at all.

As expected, eating meals high in fat did not cause my blood glucose to rise at all. In fact, many times it fell immediately after a fatty meal. In addition, consuming fats kept my blood glucose stable all day long. I felt full after meals and satiated all day long. I did not crave food even if I only ate one meal a day.

However, some fats are better than other fats. So, I focus on foods rich in healthy fats like monounsaturated fats and omega-3 fatty acids. For example, I eat lots of olive oil, avocados, salmon, and pecans. In fact, I typically get over half of all my daily calories from healthy fats now.


When we don’t have enough glucose to fuel our bodies, our body uses ketones instead. Our liver converts fat into ketones which enter our bloodstream.  There, they are used as an alternative fuel for our bodies. This makes us very adaptable since we can use either carbohydrates or fats as our primary fuel source.

During my 3-month experiment, I measured my daily ketone levels as well. As expected, when my blood glucose levels were low, my ketone levels were higher. When my blood glucose levels were high, my ketone levels were lower. This means that my body was using ketones instead of glucose for energy.

I normally eat a mostly ketogenic diet, so my body is typically keto-adapted. I can recover from a single high-carb meal in about a day. However, I was surprised to discover that it took almost a week to return to a constant state of ketosis after eating high-carb meals for several days straight.


Under normal conditions, we get our energy from the glucose and ketones created as a result of the food that we eat. So, if we’re fasting, then (in theory) we shouldn’t see a rise in blood glucose. Even if we’re burning stored fat for energy — since that will only increase ketone levels, not blood-glucose levels.

However, the human body has some pretty clever ways of getting glucose from our muscles when we’re in desperate need. The body can break down the protein in muscles into glucose through a process called catabolysis. But this only happens in a state of starvation – not simply from intermittent fasting.

As expected, my regular intermittent fasting schedule (i.e. one meal a day) kept my blood sugar relatively stable throughout the day. It would gradually rise after dinner and through the night. Then it would drop during the day, leveling out at the bottom of the normal range a few hours before dinner.


When we’re exercising, our bodies need energy in any way that they can get it. So, when we’ve exhausted free blood glucose and ketone bodies, our bodies will draw energy from their reserve glucose stores. These reserve glucose stores come in the form of glycogen stored in our liver and muscles.

As expected, exercising caused spikes in my blood glucose even while fasting. Moderate (fat-burning) exercises caused a quick rise and gradual decline in blood glucose over time. Intense (cardio) exercises caused an even higher spike in blood glucose, followed by a gradual decline.

As a result, I now try to exercise in the morning when my blood glucose levels are naturally higher. Exercising (on my normal intermittent fasting schedule) feels much easier in the morning when I have more available blood glucose than right before dinner when I’m much lower on free blood glucose.


The dawn phenomenon is a natural rise in blood sugar that happens as you are preparing to wake for the day. It’s caused by hormones signaling to your body that it’s time to wake up.

This was a bit of a surprise to me since I had not heard of the dawn phenomenon before I began using a CGM. However, as the scientific literature suggests, my blood sugar levels began to rise a few hours before I woke up each day and continued to decline throughout the day.


When our body is under stress, the adrenal glands signal to the body to quickly produce glucose. This causes blood glucose levels to rise in preparation to fight or flee from a potential threat. However, in modern society, most stressors are not physical threats, but rather, mental and technological triggers.

I was surprised to discover how much my blood glucose levels rose immediately before and during presentations for new clients. I assume a large part of the increase was my brain’s need for quick and abundant energy for my live performance. However, other stressors also caused a similar response.


Analyzing three months’ worth of blood glucose data has helped me confirm most of what I had expected from the scientific literature on the subject. However, seeing the real-world data confirm the theoretical models in the literature was quite beneficial.

In addition, there were a few surprises that I hadn’t been expecting that have really helped me to solidify my diet and exercise routine. For example, there are hidden sugars in just about everything. In addition, eggs are one of the best foods to fill you up without raising your blood glucose levels.

Now, based on everything I’ve learned, I feel confident that I can continue moving forward with my diet and exercise without needing a CGM long-term. However, if I make any significant changes to my diet or exercise, I will likely wear one for a month or two in order to see the impact of my changes.

To learn more about how to analyze your own data, please check out my online courses on Data Science.

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