You've heard about intermittent fasting. Maybe a colleague dropped 5 kilos "just by skipping breakfast". Or you read it destroys muscle and messes with your hormones. Or both, in the same week. Welcome to nutrition — where everyone has a strong opinion and the actual evidence quietly gets drowned out. So here's what the science actually says. And what I've seen over 20 years of coaching real people.
Skipping breakfast — sacrilege or common sense?
Let's start with the elephant in the room. For decades, conventional wisdom said breakfast is the most important meal of the day. Then intermittent fasting arrived and said the opposite. So — who's right?
Actually, both are — and it's mostly a question of semantics. The word "breakfast" literally means break the fast. It refers to your first meal after the overnight fasting period — whether that's at 7am or noon. The time is irrelevant. The meal itself matters.
What remains true and important: your first meal should be your most substantial. A coffee and croissant inhaled in four minutes on the way to work is not a meal — it's a caloric misunderstanding. Whenever you eat, what you eat counts.
Before the industrial era and food available everywhere at all hours, people didn't eat from 7am to 10pm. They started work at sunrise but their first meal was often around 9am. Four meals a day in an 8 to 10-hour window — and the rest of the time, they fasted. What we call "intermittent fasting" today was simply the normal way humans ate for millennia. We didn't invent anything. We just rediscovered it.
The science of fasting — what actually happens inside you
Fasting isn't a trend. It's a biological mechanism deeply embedded in our physiology. When you stop eating, your body doesn't go into panic mode — it goes into cleaning and regeneration mode. Three mechanisms do the heavy lifting.
Autophagy — the cellular deep clean
This is the mechanism that earned Yoshinori Ohsumi the 2016 Nobel Prize in Medicine. Autophagy (from the Greek: "self-eating") is your cells' self-cleaning system. During fasting, cells recycle their waste products, eliminate damaged proteins and toxic cells, and replace them with healthy new ones.
In practice? Less systemic inflammation. Lower risk of chronic disease. A body that genuinely repairs itself from the inside. And skin that looks different — because the cells are actually being renewed. Autophagy only activates during fasting. Your body is simply waiting for you to give it the time.
Gluconeogenesis — your body makes its own fuel
Without dietary glucose, the liver doesn't sit idle. It manufactures glucose from lactate, amino acids and stored fat. Think of it like your brain — normally powered by sugar — finding another socket and getting its energy from somewhere else entirely. Elegant, right?
The result: a mental clarity that often surprises people during fasting. Many of my clients describe sharper focus in the morning when fasting. The science explains it — the brain actually runs more efficiently on ketone bodies than on glucose. Try it, and you'll understand why monks have been meditating on empty stomachs for centuries.
Ketosis — fat-burning mode
When glucose reserves are depleted, the body begins burning stored fat as its primary energy source. That's ketosis. Energy becomes stable and consistent, without the peaks and crashes of glucose metabolism. Visceral fat — the most health-problematic type — begins to mobilise.
Fasting and HGH — the connection nobody tells you about
This is where it gets genuinely interesting. And it's what most articles on fasting either don't mention or skim over in a single sentence. HGH — human growth hormone — is your primary anti-ageing hormone. It regenerates your tissues, burns visceral fat, maintains muscle mass and feeds your brain. And fasting is one of the most powerful levers to stimulate it naturally — no injections, no side effects.
The mechanism is simple: when insulin drops (because you're not eating), HGH rises. These two hormones are antagonists — when one is high, the other is low. Our modern eating habits — snacking every two hours, always having something in hand — keep insulin chronically elevated. And HGH, chronically suppressed. Fasting breaks that cycle.
This is why I always combine fasting with strength training for my clients. Training stimulates HGH through muscular stress. Fasting stimulates it through the insulin drop. Together, it's a multiplier effect. And sleep before 11pm — which releases 70% of your daily HGH — completes the picture. Three levers, one result: a body that genuinely regenerates.
The health benefits — what the research confirms
Right. Enough biochemistry. Here's what it looks like in real life, confirmed by studies and by 20 years in the field:
- Reduced systemic inflammation — autophagy cleans up the damaged cells that feed chronic inflammation. Less joint pain, clearer skin, faster recovery.
- Improved insulin sensitivity — fasting recalibrates insulin response. Less fat storage, more stable energy, sharper focus.
- Gut microbiome regeneration — fasting gives the microbiome time to rebuild. A healthier gut means stronger immunity and more stable mood.
- Improved cognitive performance — ketosis fuels the brain more consistently than glucose. Mental clarity, concentration, memory.
- Slowed cellular ageing — autophagy + HGH + reduced inflammation acting together directly on biological ageing rate.
The physical benefits — what happens to stubborn fat
Here's something rarely explained about stubborn fat. When the liver doesn't have time to eliminate toxins — because it's constantly busy processing, sorting and storing food that keeps arriving — it does something quite clever: it packages the toxins with fat and stores them together in adipose tissue.
This is why some fat layers resist despite diet and exercise. They contain toxins the liver never had time to process. Fasting finally gives the liver the time to do its detox work — and in doing so, releases those stubborn fat stores. Not magic. Just biology we'd forgotten.
Add to that the complete hormonal rebalancing that fasting triggers — improved leptin sensitivity (the satiety hormone), better cortisol response in fat cells during exercise, and the HGH stimulation that drives lean muscle development. The result is a body that looks and feels "leaner" and more toned, even without dramatically changing what you eat.
No yo-yo effect — and that's the fundamental difference
This is one of the most important findings about intermittent fasting — and what fundamentally separates it from conventional diets. It doesn't affect your basal metabolic rate.
Severe calorie-restriction diets (below 1200 kcal/day) trigger your body's survival mechanism: metabolism slows, fatigue sets in, the body starts storing everything it receives. That's the yo-yo mechanism — and it's why strict diets fail 95% of the time in the long run.
Intermittent fasting, instead, puts the body under mild, adaptive stress. There's no calorie restriction — there's a time window. The body understands the difference. It optimises instead of panicking. Cells strengthen. And when you eat, you eat properly — not in survival mode.
The types of fasting — which one is for you
First, one important thing: don't think of fasting as a diet or a deprivation. It's a health tool — and like any tool, there are several versions depending on the goal.
Window fasting 16/8 (men) · 14/10 (women)
You eat in an 8-hour window (men) or 10-hour window (women). The rest of the time: water only. That's genuinely it. It's not really a "fast" in the strict sense — it's just eating with common sense. No significant side effects. All the fasting benefits except deep autophagy. This is where everyone should start. → See the complete practical guide
5/2 or 6/1 fasting
Eat normally 5 or 6 days a week, fast 1 or 2 days (around 500-600 kcal on those days). Direct effects on autophagy and hormonal rebalancing. Side effects can be more pronounced at the beginning. My recommendation: do the window fast for 4 to 6 weeks before considering this one.
72-hour therapeutic liquid fast
No solid food for 72 hours — only water, vegetable juices and broths. Goal: trigger deep autophagy, give the organs and microbiome a complete reset. Ideal at each change of season. Requires preparation beforehand and a gradual reintroduction afterwards. Don't attempt this without preparation — and not without talking to someone who actually knows what they're doing.
Does it actually work for weight loss?
Yes. But — and this is a significant but — not magically.
Research consistently shows measurable weight loss and reduced body fat. But here's what I see on the ground after 20 years: fasting alone gives good results. Fasting combined with strength training and clean eating gives remarkable results. It's that combination — not any one piece on its own — that produces the lean, energised physique most people are actually after.
Why strength training specifically, not just cardio? Because muscle burns calories at rest. The more lean muscle you have, the higher your basal metabolic rate — and the more fasting's effects are amplified. Cardio burns calories during effort. Strength training changes your metabolism permanently. They're not the same thing.
"The goal isn't to deprive yourself. It's to give your body the time to do what it already knows how to do — clean itself, regenerate, burn its reserves."
— Patrik
What I take from all this — and what I'd suggest
Fasting isn't a trend. It's an ancestral practice that biology validates with every new study. It's not a diet. Not a deprivation. It's a tool — probably one of the most powerful and accessible ones available for improving health, energy and body composition without turning your life upside down.
Start simple. The 16/8 window fast (or 14/10 if you're a woman) is the ideal entry point. Apply it for 4 weeks. Observe what changes — your energy in the morning, mental clarity, appetite, how you look in the mirror. Then decide whether you want to go further.
And if you want the step-by-step version — how to choose your window, what to eat when you break the fast, the classic mistakes to avoid — that's in the practical guide.
A question about intermittent fasting and how to adapt it to your life?
Talk to PatrikFrequently asked questions
Sources & References
- Ohsumi Y. (2016) — Nobel Prize in Medicine — mechanisms of autophagy
- Longo & Panda (2016) — Fasting, Circadian Rhythms, and Time-Restricted Feeding. Cell Metabolism
- Ho KY et al. — Fasting enhances growth hormone secretion. Journal of Clinical Investigation, 1988
- Harvie & Howell (2017) — Potential Benefits and Harms of Intermittent Energy Restriction. Proceedings of the Nutrition Society
- Fung J. (2016) — The Obesity Code. Greystone Books