At around 6pm on Monday 1 June 2026, after dinner at home, I began a 72-hour fast.
That sentence makes it sound rather more dramatic than it felt at the time. There was no ceremony, whiteboard, or spreadsheet. No Better Life-branded monk robe, which I may now have to add to the product roadmap. We finished eating, cleared things away, drank some water and stepped into the unknown.
I had never done a fast of any kind before. Not a 16-hour intermittent fast or a 24-hour reset. Nothing. My first proper experiment was going straight to 72 hours, which is probably not the textbook beginner’s route, although for me, curiosity has never been especially good at waiting patiently in the hallway.
The reason was not weight loss. I did not start this because I felt unhealthy, sluggish or in need of punishment. At 61, I am fit, active, plant-based, and already quite tuned into my body through wearables, exercise and daily routines. But I wanted to understand the experience from the inside. I wanted to see what would happen when food disappeared for three days and I paid close attention to appetite, energy, sleep, blood glucose, ketones and mood.
There was also a broader Better Life question sitting underneath it all. We talk a lot about health as action: move more, eat better, sleep deeper, train smarter, improve the score. Fasting asks a different kind of question. What happens when the healthiest thing to do, for a short and carefully considered period, might be less?
Less input. Less routine. Less stimulation. Less noise. I wanted to find out.
The first evening: a grumble, not a crisis
Six hours in, my stomach started grumbling. That was the first message from the lower office. Nothing aggressive. More of a memo. “Dear Neil, dinner appears to have been missed from the schedule. Please advise.”
I drank water and felt fine. It was interesting how quickly I started distinguishing between hunger as a genuine problem and hunger as a familiar routine being interrupted. At that point, my body was not in difficulty. It was simply expecting the usual rhythm of an evening.
That early stage taught me something quite quickly. Appetite is partly biological, of course, but it is also behavioural. The body knows time. It knows habits. It knows that after a certain hour, in a certain kitchen, with a certain evening pattern, something usually happens.
When that something does not happen, the first response is not necessarily need. Sometimes it is surprise.
We went to bed without incident and I remember being aware that the fast had started, although I was not yet properly “in” it. It still felt conceptual, like the first few pages of a long book where you know the difficult chapters are coming later.
Around 24 hours: now the body has noticed
By the following evening, the fast had become much more physical. I had a slight headache. My legs felt weak. My mouth was dry. My breath had changed. I had no real energy, although I did not feel ill.
The phrase I used at the time was that my body felt quiet, and that still feels accurate. It was not a mystical calm or a euphoric state. It was a kind of internal quietness, as though digestion had moved into the background and the normal noise of feeding, processing and anticipating food had reduced.
I do not want to over-romanticise that stage. I was tired. The headache was annoying. The legs were not exactly singing a motivational anthem. If anything, the first 24 to 30 hours were the least elegant part of the whole experience.
This is where the first proper decision came. I had started with the idea of a pure water fast. There is something attractive about that kind of clarity. Water only. No negotiation or little loopholes. It just sounds clean and disciplined. But at 25.5 hours, I took non-caloric electrolytes.
I am glad I did. The more I thought about it, the more I realised that “pure” is not always the same as “intelligent”. A non-caloric electrolyte does not provide meaningful energy. It does not turn the fast into a meal. It supports mineral balance, which matters when insulin falls and the kidneys excrete more sodium during fasting.
That was one of the first useful lessons. A health experiment should not become a purity contest. The body is not there to help us defend an idea. The idea needs to serve the body.
Cold, tired and strangely settled
By hour 30, I felt cold. Not freezing or worried. Just colder than normal. That was very noticeable because I am generally active and warm enough in myself. During the fast though, it felt as though my body had quietly turned down the thermostat.
That made sense. I was not eating. Digestion was not generating its usual warmth. Energy availability had changed. My body seemed to be conserving, which is a perfectly sensible thing for a body to do when the owner has decided, without much warning, to stop feeding it for three days.
I went to bed early. My stomach was still grumbly, but the first wave of uncertainty had passed. The strange thing was that hunger was not building in the way I had expected. I had assumed hunger would rise in a straight line. Hour 10 would be harder than hour 5, hour 20 harder than hour 10, hour 40 harder than hour 20, until eventually I would be staring at an oatcake with the intensity of a Bond villain. But that is not what happened.
Hunger came in pulses. A wave would arrive, feel fairly persuasive for a while, then move on. Sometimes it disappeared so completely that food stopped being the main subject in my head. I still thought about eating, because I am human and not a bronze statue of discipline, but the urgency had changed, and that in itself, was quietly reassuring.
Hour 40: the first numbers
At around hour 40, I woke with a slight headache. Overall, though, I felt OK. My body still had that quiet quality. I tested my markers: Ketones: 0.5 mmol/L; Blood glucose: 5.3 mmol/L.
That was the first measurable sign that something had shifted. A ketone reading of 0.5 mmol/L is often described as the entry point into nutritional ketosis. It was not a dramatic number, but it matched the lived experience. I was beginning to move away from the normal fed-state pattern and towards using more fat-derived fuel.
The research generally supports that broad sequence. In prolonged fasting, stored glycogen declines, insulin falls and the body gradually increases the production of ketone bodies, particularly beta-hydroxybutyrate, as an alternative fuel source. Reviews of human fasting describe changes in glucose metabolism, lipid metabolism, hormonal signalling and neuroendocrine response. That sounds technical on paper. In the body, at least in mine, it felt like low power, mild headache and a surprising amount of calm.
By hour 47.5, the change was clearer: Ketones: 1.2 mmol/L; Glucose: 4.3 mmol/L. I still felt OK.
That was the point where the numbers and my experience began to line up properly. I was not energetic, but I was stable. My appetite was quieter. Food had become more like something I was observing rather than something pulling me around the room. I found that fascinating.
There is a lot of value in noticing when an urge loses power. Not through force or through motivational shouting. Just through time, patience and observation.
The long middle: hour 52 and not much to report
By hour 52, I reflected that all was quiet. I was tired, but there was not much else to say.
In article terms, that sounds like a weak section. In real life, it was probably one of the most important parts of the fast. Nothing dramatic happened. There was no cinematic breakthrough. No heroic sunrise moment. No sudden deep wisdom arriving via the kettle. It was just quiet.
That middle stage felt like a useful corrective to the way we often talk about health. So much of modern wellbeing is framed as improvement through action. More protein, steps and strength work. More sleep data. More sunlight. More consistency. More tracking.
I believe in many of those things. I use many of those things.
Still, during those middle hours, the lesson came from doing very little. I was not training hard. I was not trying to increase strain. I was not attempting to turn fasting into another performance metric. I stayed warm, hydrated steadily, used electrolytes, moved gently and watched what happened.
Perhaps that is one of the most overlooked parts of health: knowing when not to add more.
What the studies say, and what they do not say
This is where I think we need to be careful.
There is real scientific interest in fasting, although the confident claims online often run ahead of the evidence. Krista Varady, professor of kinesiology and nutrition at the University of Illinois Chicago, reviewed studies on water fasting and Buchinger fasting with colleagues. Her public summary was admirably blunt: “a lot of work, and all those metabolic benefits disappear.”
That quote made me smile because it punctures some of the fasting mythology. It also matters because her team found that weight and metabolic markers can move during prolonged fasts, while many improvements appear short-lived once eating resumes.
The same UIC summary reported that people fasting for five days lost about 4% to 6% of body weight, while seven to ten day fasts were associated with 2% to 10% loss. The review also noted common side effects such as headaches, insomnia and hunger. That fitted my own experience rather neatly, especially the headache and the sleep disruption risk, although my fast was shorter than the studies reviewed.
On the cancer and longevity side, I am even more cautious. Reviews discuss mechanisms such as insulin reduction, metabolic switching, cellular stress responses and autophagy. Autophagy is often described rather loosely online as a kind of internal recycling system, which is directionally helpful but too simplistic. The biology is complicated, tissue-specific and not something most of us can measure from a kitchen table with a glucose monitor and good intentions.
I do think fasting may have a role in metabolic health and self-awareness for the right person. I do not think my 72-hour fast proves I have reduced my cancer risk. That would be far too big a claim.
A better conclusion is more modest. My body adapted. My ketones rose. My glucose fell. My appetite changed. My energy shifted. I learned something useful.
That is enough.
Hour 64: useful data, not a trophy
At hour 64, the numbers had moved significantly: Ketones: 2.4 mmol/L; Glucose: 3.6 mmol/L. I was hydrating with electrolytes and felt OK.
That was probably the deepest metabolic point of the fast. It was also the point where I was most aware of the tension between curiosity and common sense. Rising ketones can become strangely satisfying when you are tracking them. Glucose falling can feel like evidence that the fast is “working”. For someone who likes data, and I do, that can become a trap. Numbers are useful because they help you understand what is happening. They are not there to become a scoreboard.
So I kept coming back to symptoms. Was I: Dizzy? No; Confused? No; Shaky? No; My heart doing anything odd? No; Cold and tired? Yes; Fundamentally OK? Yes.
That distinction mattered. Low glucose in a fasting state can be more tolerable when ketones are elevated, because the brain has access to alternative fuel. Even so, low glucose deserves respect. NHS guidance describes low blood sugar as usually below 4.0 mmol/L and advises treatment when it occurs, particularly where symptoms are present. I was not panicking about the number, but I was paying attention.
The end: 72 hours, glucose at 3.0, and soup
At the end of the full 72 hours, my glucose was 3.0 mmol/L and ketones remained elevated.
That was the finish line, and it was also a clear signal to eat. I had completed what I set out to do. Continuing would not have made the experiment more meaningful. It would only have made it more stubborn.
My first meal was deliberately small: a bowl of soup, a couple of oatcakes, a banana and some dark chocolate.
The soup was the right choice. Warm, simple, gentle. The oatcakes gave a slower carbohydrate return. The banana was easy and familiar. The dark chocolate was less about nutrition and more about being a civilised human being again.
Eating after three days felt different. Taste was sharper. Texture was more obvious. Warmth felt comforting in a way I might not normally notice. I ate slowly, partly because that was sensible and partly because the whole thing deserved a slower ending. And I felt good. Not ecstatic. Not transformed. Just good.
What I think I learned
The most useful lesson was that hunger is not one thing.
At different points, it felt like habit, routine, physical emptiness, boredom, anticipation and genuine fuel demand. Lumping all of that under one word does not really do it justice. Fasting made those differences easier to see.
Another lesson was that tiredness does not always mean distress. I had low energy for much of the fast, especially after the first day, yet I remained mentally clear and emotionally steady. I would not have wanted to do hard exercise, make major decisions or sit through a badly chaired board meeting, although that last one is questionable even when fully fed.
I also learned that support is not failure. Taking electrolytes was sensible. Wearing warm clothes was sensible. Going to bed early was sensible. None of that diluted the experience. It probably made it safer and more useful.
The wearables and home tests helped too, although only because I kept them in perspective. My ketone and glucose readings gave structure to what I was feeling. They did not tell the whole story. They certainly did not replace judgement.
The deeper lesson, I think, was about the relationship between discomfort and danger.
Some discomfort is simply unfamiliarity. Some is adaptation. Some is a warning. The skill is learning to tell the difference without becoming reckless or timid. That feels very Better Life to me.
Would I do it again?
Yes, I think I would. Not casually. Not frequently. Not to chase a ketone number. Not because I now think everyone should do it.
For me, as a healthy, active 61-year-old with an interest in longevity, metabolic flexibility and self-awareness, the fast was worthwhile. It gave me a direct experience of something I had previously only understood as theory. It made appetite more visible. It showed how adaptable the body can be. It also reminded me that adaptation has limits and that a calm body still needs sensible decisions.
I would be very cautious about recommending a 72-hour fast to anyone with diabetes, a history of disordered eating, low body weight, significant medical conditions, medication considerations, pregnancy, or any concerns around blood sugar regulation. I would also suggest that a first-time fast does not need to begin at 72 hours. There is probably a more sensible ladder than the one I climbed.
Would I change anything next time? Probably. I would plan electrolytes from the start rather than treating them as a philosophical compromise. I would also clear the diary more deliberately, because low-energy curiosity is still low energy.
My final thought is this.
A 72-hour fast did not give me a new body, a new identity or a miracle reset. It gave me something quieter and more practical. It gave me a better understanding of my own signals. And in a world full of noise, that in itself feels really valuable.
Better Life — Founder’s Journal
Real-world optimisation, written in honest questions and the clarity that follows them.