(Hint: It’s Not a Fad)
Yes, it’s legit. And it might just be the safest way to reset metabolism without wrecking your hormones. When I first got well from chronic migraines (read about it HERE) I used the Bulletproof Diet. I started the ketogenic diet before the actual book came out, but when it did I used it as my Bible. I never cheated on that diet which included 1 carb refeed day and 1 day of protein restriction each week.
Refresher: The Bulletproof Diet is a cyclical ketogenic diet. 5 days of nutrient dense of ketogenic meals, 1 day of a carb refeed (adding in a serving or two of nutrient dense carbs) and 1 day of protein restriction with protein below 25 grams for the whole day. It was meant to be a reset, to stimulate autophagy. I never heard of FGF21 until Kelly Hogan told me about it the other day.
Why Skip Protein for a Day?
Our ancestors didn’t count macros. They didn’t have to. Some days they didn’t have food, so they didn’t eat. They feasted when they did have food and did without when there was no food. That was just normal life back then. Today we call it Feasting and Fasting cycles.
Nowadays we can have any food we want brought to our doors at any hour of the day or night. We seem to do a lot of the feasting and not much of the fasting. And it shows. We are a metabolically damaged nation.
What we know now: modern science shows that a single low-protein day can spike a powerful repair hormone called FGF21. It:
- Boosts fat burning
- Lowers blood sugar
- Enhances brain function
- Supports metabolic flexibility
All without starving yourself.
Have you heard of the “Sugar Diet”?
Social media is raving about the “sugar diet” (hello glucose spikes!). Recently I had a conversation with Kelly Hogan about the “Sugar Diet” and how it is “working” for some people. The reason I put working in quotes is just because the scale might be moving, there are a lot of other things to consider where maybe it isn’t working, you know. Anyway, Kelly was prepping her weekly YouTube post and it was about this FGF21 hormone and she did a brilliant job breaking it all down. You can listen to it HERE. It is good. All of Kelly’s Youtube videos are good.
More about FGF21:
Fibroblast Growth Factor 21 (FGF21) is a metabolic hormone primarily produced in the liver (but also in fat and muscle tissues). It plays a key role in:
- Regulating energy balance
- Enhancing fat burning
- Improving insulin sensitivity
- Triggering ketogenesis
- Supporting metabolic flexibility, especially during fasting or protein restriction.
FGF21 levels naturally rise in response to fasting, ketogenic diets, protein restriction, and cold exposure. All of those are ancestral survival signals. It helps the body switch into a fat-fueled state, conserve resources, and optimize energy when the body thinks it is in food scarcity.
So how do we tap into this FGF21 magic?
One simple way: take a short break from protein like I used to do when I followed the Bulletproof Diet all those years ago. Just one day a week at most. Think of it like a metabolic flex because it is a disruption that signals the body to adapt and shift gears.
We tend to eat in patterns (same macros, same meals), and the body gets a little too cozy with that routine. But drop the protein and bump up the fat for a day, and suddenly, your metabolism goes, “Wait… what’s happening here?” That disruption can trigger fat-burning, ketone production, and FGF21.
Bonus: using fat instead of sugar as your “fuel filler” means your liver gets a break, not a beating.
Here is how I do it
Your one-day protein reset also known as A Fat Fast:
- Focus on healthy fats: egg yolks, MCT oil, butter, fatty cuts of meat, or heavy whipping cream
- Avoid protein powders, lean meat, collagen. The goal is to keep protein below 30grams for this one day. Do not do this more than 1 day a week.
- Keep carbs low to zero.
- Bonus: go for a walk, hydrate, and support the liver (hello, taurine and bitters)
Who Should Skip This?
- If you’re underweight, pregnant, breastfeeding, or recovering from illness, stick to eating nutrient dense meals. Do not skimp on calories, ladies.
- If you feel worse after trying, your body may not be ready. Heal first. Fast later.
Bottom Line
One day a week. Not every day. That’s the ancestral rhythm.
You can also do this the other way around with a Protein Fast (eating high protein and low low fat) but this does not trigger FGF21. It is still a metabolic flex that can break weight loss stalls.
My advice is to skip the “Sugar Diet”. Your liver will thank you for not poisoning it with excess fructose.
Your mitochondria will thank you for the boost in fuel.
Heck, your mood might thank you because ketones make brains happy.
Disclaimer: This information is for educational purposes only and is not medical advice. I am not a doctor. I’m simply sharing personal experiences and observations. Always consult a qualified professional before making changes to your diet or health routine.
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