The Science Behind Moving (Gently) During FMD
Standing in line at my local coffee shop, I overheard two women excitedly planning to combine their new Fasting Mimicking Diet with their CrossFit challenge. My stomach knotted up. Three years ago, I would've jumped into their conversation with enthusiastic support. Spoiler alert: that would've been terrible advice.
And that's when I realized we all have this weird relationship with exercise during FMD. We either go full couch potato mode or try to maintain our regular CrossFit schedule while eating 800 calories of olives and crackers. Neither approach is optimal, friends.
Let's get nerdy for a second. Recent research, including that fascinating study on weight loss cleansing aging cells, shows that mild movement during fasting states can actually enhance cellular cleanup. Tim Ferriss recently discussed on his podcast how low-intensity exercise during fasting periods might amplify autophagy benefits.
But here's the catch: your body is already working overtime during FMD. It's switching fuel sources, cleaning house at the cellular level, and basically doing a complete systems reboot. Adding intense exercise is like trying to defrag your computer while rendering a 4K video. Not ideal.
What Actually Works (From My Trial and Error)
After multiple FMD cycles (and one particularly memorable gym fail on day 3), here's what I've learned:
Days 1-2: Light walking, gentle yoga, or stretching. Think "movement snacks" rather than workouts. I aim for 20-30 minutes of easy movement, usually a neighborhood stroll while listening to podcasts.
Days 3-4: This is when energy typically dips hardest. I stick to restorative yoga or literally just walking to the mailbox. Your body is deep in ketosis now – respect the process.
Day 5: Energy often rebounds slightly. A longer walk or gentle swim feels amazing. But still no HIIT classes, please.
Real Talk: When to Skip Movement Entirely
Let's be honest here – some days during FMD, getting off the couch feels heroic. And that's totally fine. I've had cycles where day 3 meant horizontal Netflix marathons, and guess what? The FMD still worked its magic.
Signs to rest completely:
- Dizziness or lightheadedness
- Unusual fatigue (beyond normal FMD tiredness)
- Any heart palpitations
- Just not feeling it (seriously, honor this)
The Post-FMD Exercise Return
Here's something nobody talks about: jumping back into intense exercise immediately after FMD can feel awful. Your glycogen stores are depleted, and your body needs time to readjust. I learned this the hard way when I attempted a spin class the morning after finishing FMD. Let's just say I became very familiar with the studio's bathroom.
Instead, ease back over 2-3 days. Start with your FMD-level activities and gradually increase intensity. Your body will thank you.
My Current FMD Movement Protocol
Because I know you want specifics (as one does), here's exactly what I do now:
- Pre-FMD: Normal workouts until the day before starting
- FMD Days 1-5: 20-30 minutes daily of gentle movement, usually walking
- Post-FMD Days 1-2: Continue gentle movement
- Post-FMD Day 3+: Gradually return to normal exercise
The beauty? This approach maintains some cardiovascular fitness without sabotaging the FMD benefits. Plus, those gentle walks become almost meditative when you're in that fasting state.
The Takeaway Nobody Wants to Hear
Exercise during FMD isn't about maintaining your gains or hitting PRs. It's about gentle movement that supports the fasting process without overwhelming your system. Think of it as giving your body just enough activity to stay mobile while it does its cellular spring cleaning.
And remember – whether you're doing ProLon® or DIY FMD, the same principles apply. Your body is doing incredible things during these five days. Sometimes the most athletic thing you can do is rest.
What's your experience with exercise during FMD? Have you found your sweet spot, or are you still figuring it out like the rest of us? Drop a comment below – I'd love to hear what works (or spectacularly doesn't work) for you.
Disclaimer: I'm not a medical professional, just someone who's done FMD more times than I can count and learned from plenty of mistakes. This post reflects my personal experience and research. Always consult with your healthcare provider before starting any fasting protocol, especially if you have underlying health conditions. And seriously, please don't attempt that CrossFit class on day 3 – learn from my mistakes!