How knowing my blood sugar levels helped to tackle my running goals.

As he started to get into endurance running, Dan wore a CGM to learn how to take control of his body's metabolism and run 53 miles.

Dan is a runner on a personal quest to find out how to best lead an informed, healthy lifestyle. He has used his engineering background, passion for nutrition, and global experience to optimize his athletic performance and his life, especially at the intersection of digital and physical health.

During training for an endurance race, he used Levels to track and adapt his nutrition before, during, and after the race. Understanding the data behind his metabolic health helped Dan to improve his nutrition and performance. Here's what he learned.

"How can you challenge yourself to know yourself better?" My answer, surprising to myself even, has been running. In two years' time I went from struggling through a 5k to running an ultramarathon and smashing through my goal.

The Midstate Mile in Tennessee would be a challenge for myself. I wanted to push into unknown territory physically and mentally in order to know myself better. For background, the race entails running a 1.1 mile loop every 20 minutes. The loop is a trail course that includes 340 feet of vertical gain. My race would end when I give up or fail to complete the loop within 20 minutes. My goal: to run a full marathon distance, something I'd never done.

Ultra training comes down to three things: nutrition, stamina, and fitness. The body needs carbohydrates and sugars to exert itself steadily; the heart and cardiovascular systems need to be strong; the mind and legs need the strength to endure the grueling hills. Understanding my glucose response helped me learn how to fuel and train to be sure my body and mind were ready.

The Before: Race Preparation

Before race day, I especially need to learn how to fuel my body, and how not to fuel my body. (I have always had a hankering for sweets and I'm curious how that affects my training.)

Physical preparation for the race requires a mix of long, low-intensity jogs or climbs and high-intensity strength work. Being a data nerd, I was excited that Levels would integrate smoothly with my watch to sync my workouts. The integration gives me a complete picture of my training and nutrition without having to manually input each workout.

The low-intensity aerobic exercise provides an opportunity to learn how to fuel. I need a constant stream of calories over a period of hours. Important things to know for race day! This exercise also helps my cardiovascular strength. I decide to eat carbohydrates in the form of home-made protein balls that digest slowly. After experiencing bloating from overeating a couple times, I knew I needed to cut back on my mid-exercise fiber and carbohydrate intake. I then opt for foods that replenished my sugar and salt levels. Organic baby food did the trick, since it's quick and easy and gave me quick hits of sugar and some easy-to-digest calories. Spacing the fruit squeezes out every 40 minutes gave me the sugar intake I needed for sustained energy.

High-intensity strength training helps me build up my baseline strength and push myself in short bursts. Heavy meals don't usually sit well with me before intense workouts, so I eat high-carb foods loaded with carbohydrates and protein, like salmon, eggs, rice, and sweet potatoes. My glucose levels respond well too!

To prepare for the overall increase in workouts, I do my best to eat a consistent breakfast of two eggs, greens, and cheese. Sometimes I mix in easy-to-digest fruit. One of my favorite things are potatoes, but I quickly learn I have a negative response, especially in the morning!

The training data and experimentation reveals a few specific keys that I can keep in mind heading into race day: (1) a steady stream of sugars and simple carbs during prolonged activity helped me perform my best. (2) My body does not like gluten. I've avoided gluten for awhile because I find it makes me angry and uncomfortable, but nearly all my biggest spikes were from meals that included gluten. (3) Hunger doesn't mean I need food. During times I felt hungry, my glucose profile often showed a peak and steep crash. These crashes between meals were exhausting and signaled hunger pangs that weren't helpful for losing weight. My training strategy included weight loss because I knew I had to carry every extra pound up and down the steep hills!

Prior to race day, I focus on connecting the meal with the blood sugar response. The constant data feedback improves my knowledge and preparation exponentially. The last few days leading up to the race, I stock up with extra calories to build my energy stores.

The During: Monitoring

My goal for the Midstate Mile from the outset was to run a marathon. It would have been a first for me, especially on the course's steep hills.

The night before the race, I eat beef, egg, potatoes, buttered salmon, carrots, and broccolini. It was a big meal to pack in the calories before a long day of running.

I get pre-race jitters, so all I eat the morning of the race is a banana. It would at least provide some simple carbohydrates.

From training, I knew I'd need a lot of calories and a lot of water. Water was a non-negotiable, and I would drink 15-20 ounces every 20 minutes.

To hit my recommend 200-300 calories per hour I need to eat regularly, even when I didn't feel like it. The food would help me avoid an energy crash later that is the downfall of so many first-time ultrarunners. Knowing this, the first few hours of the race I stick with high-carb, complex foods: gluten-free bread topped with peanut butter and salt, bacon, and melon. I know I can stomach these heavier foods early in the day. I even get in a non-alcoholic beer!

I know my glucose levels didn't respond well to Clif bars or similar foods, especially if I wasn't exercising at all. On race day, I stay away from these dense foods as the day got hotter and the intensity ramped up. Suddenly the hills started looking steeper! My glucose levels bottom about three hours into the race. It signals to me that I wasn't eating getting enough glucose and need to switch from more complex foods to fast, sugary fuel. The rest of the race, I mostly eat fruit. Watermelon, puréed fruit/veggies pouches, and name brand Oreo's (gluten free!) give me quick energy and didn't sit in my stomach long.

My glucose levels slowly rise as the exercise got more intense. I hit the top of my target zone 8 hours (about 24 miles) in, where it would remain for the next 9 hours. I stuck with the fruit diet with some protein-filled bacon for protein.

As the day turns to night and my knees struggle under the impact of the descents, my pace slows down until I can't complete the loop within the 20 minutes time interval. The race started at 8:00 in the morning and my last lap finishes at 12:20 A.M.

After 16 hours of running, I completed 54.8 miles, 16,600 feet of vertical gain, and 48 laps. It was good enough to finish 14th overall — far beyond what I thought my body was capable of.

Immediately after the race, I eat carbs and protein to recover and start the process of getting my nutrition back to normal. Eating entire loaves of bread and boxes of cookies helps during the race, but really throws off my usual diet and routine. Having completed the race, I'm looking forward to get out of a calorie deficit and reward myself with lots of calories over the coming days. That night, I record my lowest ever glucose reading when it temporarily dropped to 41 mg/dL. I attribute it to a deep REM sleep as my physiological systems went into full recovery mode.

The After: Takeaways moving forward

Understanding my metabolic response feels like a superpower. My CGM helped to tie together my nutrition, stamina, and fitness training to double my race goal and exceed what I thought was possible. The data compounded the impact of every training session. It also gave me the peace of mind and the space to let me focus on the mental battle of endurance racing.

I initially wanted to see the effects of my sweet tooth and optimize my nutrition to build race endurance. Now after the race, I can eat big refueling meals without causing glucose spikes because I know how my body reacts to certain foods, like gluten.

One example I found was that my metabolic system has a more stable response when I mix carbohydrates, protein, and fat in meals.

In the weeks surrounding the race, I had a 60% reduction in High Glucose events. Now I rarely if ever see glucose levels above 140 mg/dL. I lost 14 pounds of muscle and fat and gained a new appreciation of cardiovascular fitness.

After spending weeks training and monitoring myself, I learned the value of being present and deliberate when eating. Taking pictures of my food forced me to consider what I was eating, and how it aligned with my training. I can look at my glucose history and know why I feel sleepy or why I get restless sleep.

By gaining an understanding of my nutrition and exercise, I ran further than what I thought my body was capable of. It shows how a few insights can unlock a whole new potential.