As an experienced vegan with a month of consistent 48hr intermittent fasts under my belt going into this experiment, you’d expect it to at least start smoothly.
It didn’t.
You might also expect that challenges maintaining a 48hr fast only show up in the early weeks.
But that’s not what happened.
I was forced to split three planned 48hr fasts in:
Different context. Same outcome.
Key Insights
Please note: This and other articles reflect personal experimentation and are not medical advice.
The setup was wrong, despite the planning.
Food choices going into the fast weren’t aligned with what was needed, and hunger showed up clearly within the first 16 hours, forcing me to split the fast earlier than planned.
A completely different situation on the surface.
The previous week included 7 consecutive days of training. Intake wasn’t adjusted to match the increased output, and glycogen was never fully restored. (Read more about Why Even Experienced Fasters Struggle When They Start Training).
The result?
The same pattern.
The fast became unstable and had to be split.
More subtle.
By this point, my body had adapted and required a higher protein intake than earlier in the experiment.
Add in my birthday and the arrival of cake, which highlighted a clear shift in how my body was responding to sugar at this stage; combined with a lack of a clear protein anchor, pushed hunger to show up early again.
Same outcome.
Each failure had a different cause.
The result wasn’t.
This is where it’s easy to get it wrong.
In the moment, it’s natural to think:
“I couldn’t handle the fast.”
“My willpower slipped.”
“Something went wrong during the fast.”
But none of those were true.
The fasts were compromised before they started.
This idea that what you feel during a fast is often a delayed signal, rather than a real-time problem, is something also discussed by Stephen Cabral when looking at fasting and metabolic stress.
This is the most common issue I’ve recorded.
On the first Sunday coming into the experiment, I didn’t eat enough of the right things. The result was a feeling I hadn’t experienced for a very long time — unsure whether I was full or still empty.
This was the full day of eating before the fast:
Mid morning
Fruit granola
Light lunch
Vegetables with hummus
3 spoonfuls granola, yoghurt, blueberries
Vegan protein bar
Evening meal
Roasted pumpkin, red onion, cauliflower, spinach, tofu, green lentils
On paper, it looks clean.
In reality:
Everything looked “healthy”.
But it wasn’t sufficient.
This is one of the easiest traps to fall into on a plant-based diet.
If you’re reading this thinking that looks light going into a 48hr fast, you’re right. I’ll come back to this.
By Week 14, training had increased to 6 days per week.
Then came a 7-day week, including a 10km run on the Sunday.
Fuel didn’t adjust.
This was my intake that day:
7.30am overnight oats
10.00am 10km run
11.55am homemade banana protein bar
12.15pm vegan breakfast (higher fat and salt than usual)
12.45pm banana
1.40pm protein bar + tea + dark chocolate
2.20pm tofu cubes + a few spoonfuls of Greek yoghurt
3.40pm handful salted peanuts
5.00pm small tofu portion
6.45pm black beans with miso, vegetables, tofu and jasmine rice (+ leftovers with yoghurt)
On paper, it looks like enough.
But structurally, it wasn’t.
The deficit didn’t show up immediately.
It showed up 12–16 hours later, during the fast.
That’s when things broke.
Lesson:
If output increases, intake must adjust with it.
This is where it gets more nuanced.
Plant-based diets can make this easier to get wrong.
Foods are typically:
Yes, many plant foods contain protein.
But effective protein intake requires deliberate structure through foods like tofu, tempeh, and legumes.
This is explored in more detail by Matt Frazier and Robert Cheeke in The Plant-Based Athlete.
Without that structure, it becomes easy to feel like you’ve eaten enough…
When you haven’t.
And when that happens, fasts become unstable.
Once you see it, it’s hard to ignore.
If the setup is wrong, the fast becomes unstable.
And more importantly:
Hunger is not random.
It’s a delayed signal from the previous day.
This aligns with broader observations in fasting practice, where signal misinterpretation is often the root cause of failure, as discussed by Stephen Cabral.
This is where people tend to focus on the wrong part.
Trying to manage the fast while you’re in it.
That’s too late.
Protecting a 48hr fast happens before it starts.
At a high level, that means:
The exact structure matters. But the principle is simple.
You don’t protect the fast during the fast.
You protect it before it starts.
When you first start out with a 48-hour fast, you don’t need to overeat before you begin.
More food doesn’t create more stability.
In fact, it can work against you.
Overeating before a fast often creates a psychological expectation for larger refeeds later, which can destabilise the system.
What matters is not excess.
It’s structure.
Over time I’ve learned to better understand how my body is actually responding.
Pre-fast meals became more intentional.
Protein became a focus, not an afterthought.
Training and fuelling began to align.
Failures stopped feeling random.
Because they weren’t.
The biggest shift is accepting that failures will happen, and that it's ok! Learning from my mistakes has kept this experiment moving forward.
A 48-hour fast isn’t a standalone event.
It’s the result of what happened before it.
In most cases, it’s not about the fast itself.
It’s a delayed response to insufficient fuelling the day before, especially around protein and total energy.
Yes.
Protein plays a key role in satiety and recovery. Low intake before a fast often leads to earlier hunger.
You can.
But if training load increases, fuelling needs to increase with it. If it doesn’t, the fast becomes unstable. Read more on improving athletic performance with extended intermittent fasting.
It can be.
Plant-based diets are typically less calorie dense and more filling, which makes under-fuelling easier if protein isn’t structured deliberately.
The fast didn’t fail.
The setup did.
What challenges have you had when attempting a 48hr fast?
Image: Photo of the meal that compromised the 48hr fast in Week 1.