ONE is the intermittent fasting app built to keep you on track. Set your fasting duration, follow your metabolic phases in real time, and stay consistent — all in one place.
Intermittent fasting is an eating pattern that alternates between defined fasting periods and eating windows. Unlike traditional diets, it focuses on when you eat — not what you eat. Your body responds to these fasting periods by lowering insulin, burning stored fat, and triggering cellular repair through a process known as autophagy.
The practice aligns naturally with your circadian rhythm. When you extend the overnight fast by a few hours, your body shifts from glucose burning to fat burning. Studies show this metabolic switch can support weight loss, improve insulin sensitivity, and reduce markers of inflammation — without requiring a complicated meal plan.
Time-restricted eating is one of the most researched forms of intermittent fasting for beginners and experienced practitioners alike. Whether you choose 16/8, 18/6, or 20/4, the core principle is the same: give your digestive system a real break, and let your body do what it was designed to do.
Digesting
Hours 0–4 · Digestion & glucose use
Burning glycogen
Hours 4–12 · Insulin drops, glycogen depletes
Fat burning
Hours 12–18 · Ketones activated
Deep fat burn
Hours 18–24 · Deeper ketosis
Extended fast
Hours 24–36 · Cellular repair activity
From setup to first fast to long-term results — here is exactly how ONE works.
Choose your fasting duration in under 60 seconds. Pick a Quick Start — 16h, 19h, 24h, or 36h — or set a fully custom fasting window. ONE handles the transitions between your fasting and eating windows automatically so you never have to think about when to start.
What you configure
One tap. That's all it takes to begin. A live circular progress ring counts every minute of your fast and automatically tracks which of the 5 metabolic phases your body is in — in real time.
You get a push notification every time you cross into a new phase, with tips and guidance tailored to exactly where you are in your fast.
The 5 fasting phases ONE tracks
Body using energy from last meal, insulin high
Stored carbs becoming fuel, insulin falling
Fat oxidation increasing, insulin low
Ketones becoming major fuel, insulin very low
Cellular repair activity likely elevated
After your fast, ONE keeps working. Log your water, log your weight, and review your fasting history. On Premium, the AI Coach analyses your weekly and monthly data, scores your consistency, and surfaces insights — your strongest days, areas to improve, and personalised tips. Every fast makes the next one easier.
What you track
Decades of research support intermittent fasting as one of the most effective dietary strategies for sustainable weight management and overall health.
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A 2020 review in Obesity Reviews found that intermittent fasting produces weight loss comparable to continuous caloric restriction — while better preserving lean muscle mass. When you combine a fasting schedule with adequate protein during your eating window, your body preferentially burns fat rather than muscle. Most ONE users report losing 1–2 lbs per week in their first month.
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Extended fasting periods give your pancreas a rest and help reduce insulin resistance — a key driver of type 2 diabetes and weight gain. Studies show fasting can lower fasting blood sugar by 3–6% and fasting insulin by 20–31%. Better insulin sensitivity means your cells respond more efficiently to glucose, making healthy weight maintenance easier long term.
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Many people who follow an intermittent fasting schedule report improved mental clarity during their fasting hours. When your body runs on ketones — the fuel produced during fat breakdown — your brain often performs better than on a glucose-heavy diet. Research on time-restricted eating suggests it may support BDNF, a protein linked to learning and memory.
04 / 05
Chronic inflammation underlies most modern diseases. Intermittent fasting has been shown to reduce key inflammatory markers including C-reactive protein (CRP) and interleukin-6. In parallel, studies demonstrate improvements in cholesterol profiles, blood pressure, and triglyceride levels — critical cardiovascular health indicators that go well beyond simple weight loss.
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Traditional diets require counting every calorie for every meal, all day long. An intermittent fasting schedule simplifies this dramatically — you only manage what happens within your eating window. Over time, many practitioners find that intermittent fasting for beginners becomes second nature, requiring far less willpower than conventional dieting approaches.
ONE Intermittent Fasting App is built around how intermittent fasting actually works — giving you the tools to track, learn, and stay consistent without the complexity.
Live countdown with Quick Start durations of 16h, 19h, 24h, and 36h — plus a fully custom timer for any duration you choose. Gentle notifications keep you on track.
See which of the five phases your body is in — Digesting, Burning glycogen, Fat burning, Deep fat burn, or Extended fast — updated in real time throughout your fast.
Describe what you ate in plain language — e.g. "2 eggs, a chicken breast and a cup of rice" — and AI estimates your protein intake. Add ingredients by weight for more precision.
Staying hydrated during your fasting window is critical. ONE tracks daily water intake and sends timely reminders so you never confuse thirst with hunger.
Track weight trends, fasting streaks, and total hours fasted — all in one dashboard that keeps you motivated through the early weeks.
Connect ONE with Apple Health on iOS or Google Health Connect on Android to keep your fasting and health data in one place.
Everything you need to know before starting your intermittent fasting journey.
Intermittent fasting is an eating pattern that cycles between periods of fasting and eating. Rather than restricting what you eat, it focuses on when you eat — giving your body dedicated windows to burn stored fat, lower insulin, and support cellular repair processes.
ONE uses a live circular timer that starts the moment you tap "Begin Fast." It automatically detects which of 5 metabolic phases your body is in based on elapsed fasting hours and sends you a push notification each time you enter a new phase — so you always know what's happening inside your body.
ONE offers Quick Start durations of 16, 19, 24, and 36 hours, and a Custom Timer that lets you set any duration you like. Fasting sessions of 12 hours or less are not saved to your fasting history.
The app tracks 5 phases: Digesting (0–4h), Burning glycogen (4–12h), Fat burning (12–18h), Deep fat burn (18–24h), and Extended fast (24–36h). Each phase reflects a real metabolic shift — knowing which phase you're in helps you understand why you feel a certain way and what your body needs at that moment.
Yes. Protein tracking is a Premium feature. Describe what you ate in plain language — for example, "2 eggs, a chicken breast and a cup of rice" — and AI estimates your protein intake. You can also add ingredients by weight for more precision. ONE does not include a food or barcode scanner.
Yes. On iOS, ONE syncs with Apple Health. On Android, it integrates with Google Health Connect. Your fasting data lives alongside the rest of your health data.
Yes. The AI Coach is a Premium feature powered by OpenAI. It analyses your fasting sessions weekly and monthly, gives you a 0–100 consistency score, and surfaces categorised insights — achievements, strengths, areas to improve, tips, and warnings — so you get a personalised action plan, not just raw numbers.
Intermittent fasting is well-studied and considered safe for most healthy adults. ONE is a wellness and tracking tool — it does not provide medical advice. Always consult your doctor before starting any fasting protocol, especially if you have a medical condition, are pregnant, or take medication.
Every day you complete a fast, your streak grows by one. Miss a day and it resets — so streaks keep you accountable without being complicated.
ONE is free to download. Core features — the fasting timer, phase tracking, streaks, and history — are included at no cost. A Premium subscription unlocks the AI Coach and protein tracking. Current subscription options are shown inside the app.
Download ONE — free to use, no credit card required. Available on iOS & Android. Visit www.fastingtime.co/
Expert guides on fasting schedules, meal planning, and maximising your results.
Beginner Guide
Schedule Comparison
Nutrition