Fasting is one of those ideas that sounds like a modern "biohack"… until you zoom out.
For most of human history, we didn't live in a world of constant food availability. Eating was variable — seasonal, uncertain, sometimes abundant, sometimes sparse. Variability was normal.
Modern life flipped that script: food is everywhere, all the time. So fasting — done sensibly — can be seen as reintroducing a metabolic state our biology can handle, even if our culture has forgotten it.
Why fasting can make you feel more alert
There's a reason people often report a strange clarity during a fast: the body has an incentive to make you sharper when you need to go find food.
One mechanism involves orexin (hypocretin) neurons, which help regulate wakefulness, motivation, and food-seeking behaviour. As fasting deepens, ketones rise and begin contributing fuel and signalling. Ketone bodies can serve as an alternative brain fuel during prolonged fasting — and beyond fuel, they also act as signalling molecules in the nervous system.
The "new" part: autophagy and why fasting became scientifically serious
Fasting has existed forever culturally, but the cell biology behind it is comparatively recent.
In 2016, the Nobel Prize in Physiology or Medicine was awarded to Yoshinori Ohsumi for discoveries of the mechanisms of autophagy — the cell's recycling system that becomes especially relevant under nutrient stress.
That Nobel didn't "prove fasting cures disease." What it did do was validate that cells have conserved, regulated programmes for repair and recycling that we can study rigorously — and fasting is one context where those programmes change.
Why oncology is sceptical — and why that's not automatically wrong
Many oncology teams worry about:
- Weight loss, malnutrition, and muscle loss, which can worsen treatment tolerance
- Lack of definitive large trials across different cancers and regimens
- Patient variability and safety, particularly for anyone underweight, frail, or diabetic
So yes — there's emerging evidence and serious research interest. But there's also a genuine safety question: is fasting helping, or is it pushing someone closer to malnutrition?
What your body is doing during a fast — hour by hour
0–4 hours: fed state
Digestion and absorption dominate. Insulin rises. Glucose is used and stored as glycogen.
4–12 hours: early fasting
Insulin falls; glucagon rises. Liver glycogen helps keep blood glucose steady. Fat breakdown begins.
12–16 hours: "switching" begins
Glycogen drawdown continues. Fat oxidation rises. Hunger often comes in waves, not a straight line.
16–24 hours: ketones become noticeable
Ketone production increases. Your liver generates them by burning body fat. CGM curves often stabilise.
24–36 hours: deeper fasting physiology
Lower insulin. Growth hormone increases to protect muscle while stored fat is burned.
Fasting signals cells toward autophagy — the body "cleaning house" within cell walls.
36–48+ hours: the deep fast
Ketones may rise further. Autophagy is in full swing — cells are recycling waste materials,
pathogens and viruses are destroyed, and the immune system starts to reset.
Stay hydrated and take minerals with water.
Autophagy isn't an on/off switch at hour X. It's a set of processes influenced by nutrient status, sleep, exercise, protein intake, and stress.
Why fasting is being studied with chemotherapy
"Differential Stress Resistance" (DSR): protect normal cells.
Preclinical work suggests fasting can push healthy cells into a more protected, maintenance-oriented
state — reducing growth signalling and increasing stress resistance.
Cancer cells may not downshift as cleanly.
Many cancer cells keep pro-growth pathways active and may be less able to enter that protected mode,
potentially making them more vulnerable to treatment stress under fasting conditions.
Strongly supported in animal work; being tested in humans.
My fast is chemo-specific: why it "straddles the IV"
I'm not fasting as a lifestyle badge. I'm using it as a timed tool around chemo.
The intent is simple: be in a "low growth signalling / higher stress-resistance" metabolic state during the exposure window, then refeed carefully to support recovery.
This is not a universal recommendation. It only makes sense if you're cleared by your team, not losing dangerous weight, and not at risk of malnutrition. If you're underweight, fainting, diabetic, or already struggling with intake — fasting can be a bad call.
The refeed matters as much as the fast
The gut microbiome has been resting during the fast — something evolution taught it to do, but that most modern humans have never experienced. What you put back in, and when, is critical. I refeed in staged steps:
- Bone broth + sprout shoots — wait ~2 hours.
- Avocado + poached egg — wait ~2 hours.
- Greek yoghurt + berries + a few nuts — wait ~2 hours.
- Tuna/chicken + vegetables — a proper protein-forward meal.
The point
I'm doing this for one reason: I want the best chance of a fight — without doing something that undermines treatment by stripping muscle or nutrition.
Fasting is not the hero. Consistency is. It's one lever inside a wider 1% protocol: hydration, protein, sleep, movement, breathwork, mindset, tracking, recovery.
Medical note: This is my personal experience and reading of the science — not medical advice. If you're considering fasting around chemotherapy, involve your oncology team and a cancer-specialist dietitian first.