Fasting FAQ

Intermittent fasting (IF) isn't a diet — it's an eating schedule. Instead of telling you what to eat, it tells you when to eat. The most popular format is 16:8, where you fast for 16 hours and eat within an 8-hour window. But there are many variations: 18:6, 20:4, OMAD (one meal a day), and the 5:2 approach where you eat normally 5 days and restrict calories 2 days. I personally started with 16:8 because it felt manageable, then gradually moved to 18:6 as my body adapted.

No. Fasting is not safe for everyone. You should definitely talk to a doctor before starting if you: are pregnant or breastfeeding, have a history of eating disorders, have diabetes (especially Type 1), take medications that require food, are underweight, or have any serious medical condition. For most healthy adults, short-term fasting (16-24 hours) is generally considered safe. But "generally" doesn't mean "universally." I started only after getting clearance from my doctor, and I recommend you do the same. This tool is for tracking, not medical advice.

Black coffee, plain tea, and water are generally considered fine during a fast — they have virtually no calories and won't spike insulin in most people. The debate starts when you add stuff: milk, cream, sugar, artificial sweeteners. Some purists say anything other than water breaks a fast. I take a practical approach: a splash of oat milk in my morning coffee (maybe 20 calories) hasn't stopped my progress. But if you're fasting for specific metabolic benefits like autophagy, you might want to be stricter. Experiment and track your own results — that's what this tool is for.

It depends on what you mean by "results." For me, mental clarity and stable energy improved within the first week. Weight changes took about 3-4 weeks to become noticeable. The calculator's Goal Planning tab gives you estimates based on your protocol and consistency, but honestly, everyone's body is different. Some people lose weight fast. Some plateau for weeks then drop suddenly. My advice: track for at least 30 days before judging whether it's working. And measure more than just weight — energy, sleep, mood, and focus matter too.

Start with 16:8. It's the gentlest entry point. You basically just skip breakfast (or dinner, whichever fits your life better) and eat within an 8-hour window. Most people already fast 8-10 hours while sleeping, so extending it to 16 isn't a huge leap. Once you're comfortable with 16:8 for a few weeks, you can experiment with 18:6 or even 20:4. Don't jump straight into OMAD or extended fasting — that's a recipe for burnout. I made that mistake early on and had to reset. Slow and consistent beats aggressive and inconsistent every time.

Short-term fasting (16-24 hours) actually increases metabolic rate slightly, largely due to rises in norepinephrine and human growth hormone. It's chronic, severe calorie restriction over months that can slow metabolism — not intermittent fasting. That said, if you combine IF with extreme undereating during your eating window, you might run into problems. The key is eating enough during your feeding window. I use the calculator's metabolic analysis to make sure I'm not underfueling myself. Again, this is general info — your doctor knows your specific situation better than any blog post.

Yes, and many people (myself included) actually prefer fasted workouts. Low to moderate intensity exercise — walking, yoga, light jogging — feels great fasted. For high-intensity training or heavy lifting, it depends on your adaptation. I do my design work in the morning fasted (great focus), and save my actual gym sessions for after my first meal. The Eating Window Planner in the calculator helps you align workouts with your eating schedule. Experiment and see what feels right for your body.

Your data is stored entirely in your browser's localStorage. That means it never leaves your device. I don't have a server, I don't have a database, and I literally cannot access your fasting logs even if I wanted to. The downside: if you clear your browser data or switch devices, your history disappears. The upside: complete privacy. You can export your data as CSV anytime from the Report tab if you want a backup. I built it this way because I don't want anyone's health data, including my own, floating around on servers.

Then you break your fast early. It happens. I've done it dozens of times — social events, bad sleep, stress, or just plain hunger. One broken fast doesn't undo your progress. The consistency score in the Trend Tracker is calculated over time, not per session. If you hit your target 80% of the time, you're doing great. Perfection isn't the goal; sustainable habits are. Log it honestly, note why it happened, and start again with the next meal. No guilt needed.

It's an estimate based on general metabolic research and population averages. The ketosis and autophagy timelines are rough guides — individual variation is massive depending on your diet, activity level, metabolic health, sleep quality, stress, and genetics. I use the metabolic tab as a reference point, not a definitive truth. If you want precise metabolic data, you'd need blood ketone meters, continuous glucose monitors, or lab tests. This calculator gives you a useful framework to think about what's happening in your body, but it's not a medical device.