Vox Performance Project: Maria

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Do electrolytes and carbs matter? My personal experience while fasting

Hello, it’s Maria. For nearly two years, I practiced triathlon as a hobby without fueling or hydrating during training. I thought training on an empty stomach would make my body stronger, but I was wrong. I suffered from seven injuries, including three sprained ankles and two injuries to my lower back and knees. If you’ve also experienced an injury, you know how frustrating it is to have to stop training, lose your fitness, and start all over again.

It wasn’t until I joined the Vox Performance Project that I started properly fueling and hydrating during my workouts. It’s the first time in my life that I’ve gone more than six months without an injury (I am so happy!). I cannot say that carbs and electrolytes are the only reason for my lack of injuries, but they have helped me a lot to have much more energy and go at the same speed with less fatigue.


Experiments: Fasted sessions vs Non-fasted sessions

Now, let’s talk about my experience with glucose sensors. After getting the Supersapiens sensors, I immediately became obsessed with experimenting with them. They helped me create awareness of what was happening with my body. I’ll share my findings while experimenting with fasted and non-fasted sessions for high-intensity and easy trainings. First, let’s talk about fasted sessions:


1) Fasted Sessions

For hard anaerobic sessions, I felt weak and had more cramps than usual. My glucose levels were always low (70-80mg/dl), and they decreased as time went on. Not fun at all! I quickly learned that I will not be doing hard trainings while being fasted again.

For easy, aerobic and constant sessions, I felt normal energy levels even though the glucose sensor showed me low glucose levels (85-90mg/dl). Sometimes, 40 minutes into the session, I’d suddenly feel with higher energy levels, which were also reflected in higher glucose levels (they increased up to 130mg/dl). I felt that while being fasted, my body needed a very long warm-up before feeling full of energy. But unfortunately, this high energy feeling only lasted for about 30 minutes, and then the energy and glucose levels started to drop. 

Based on my experience, I recommend doing fasted sessions only if they’re easy or technique sessions for no longer than an hour. I found that taking electrolytes without sugar, such as the 250mg sodium capsules from Precision Fuel & Hydration, worked perfectly for me for these sessions. Also, I prefer to do these easy trainings early in the morning since I don’t need to wake up and fuel in the middle of the night heheh. 


Fig 1. My performance during a 2-hour easy cycling session while being fasted for 16 hours. I felt with normal energy the first 30 minutes (95mg/dl), then I felt full of energy (130mg/dl) and at the end I felt that my energy levels dropped (100mg/dl). This was reflected in my glucose levels.


2) Non-fasted sessions

For hard/anaerobic sessions, I included a pre-workout meal high in carbs three hours before the session and a 30g gel with or without caffeine during the trainings. I felt full of energy, especially when I included the caffeine gel, which made me feel a little bit hyperactive. I didn’t experience cramps and had less post-workout pain compared to when I was fasted. I noticed that my glucose levels were consistently high during these sessions, averaging over 110mg/dL.

For easy aerobic sessions, I felt that a 3-hour pre-workout meal was more than enough. Maybe if the session was moderate, a banana 10 minutes before exercising could help to have higher glucose levels. I do not feel that I need to consume gels for these sessions, and if it is too easy, doing it fasted could also be a good option, especially when you don’t feel like eating! 


What I learned…

Fasting while training is only a good option for easy/technique aerobic sessions of no longer than an hour. Even though my glucose levels weren’t optimal, I didn’t feel like I needed extra fuel to complete these sessions. On the other hand, fasting wasn’t a good option for moderate/hard training. Although it was possible to complete these sessions, my performance suffered, and my heart rate levels were higher. Electrolytes and carbs give me the energy I need to push through tough workouts.


Fig 2. Glucose score during similar cycling Zwift sessions. Left side in green was while fueling during and before the training (Score: 82 over 100, Nice!). Right side in blue was while fasting (Score: 57 over 100, oh no!).


We come to the end of this blog… but before saying goodbye to each other, please:

Don’t Forget to ALWAYS HYDRATE!

Fasting doesn’t mean to not hydrate. We are constantly losing electrolytes. Even if a session feels easy, our bodies are still losing electrolytes. Make sure to replenish with sodium and magnesium not only while training, but also before and after high intense sessions. They are the key for recovery!

If you still don’t hydrate and fuel, this is the signal you needed to start doing it! You won’t regret it. You will immediately feel the difference in the effort that you have to make while cycling at the same speed. 



Until next time, stay hydrated and keep enjoying your trainings!

Maria Paula

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