Periodic Fasting · The Fast Diet
5:2 Diet Calculator
Eat normally 5 days a week. Restrict to ~500 calories on 2 non-consecutive days. Calculate your targets for both types of days.
Step 1 — Choose Your Protocol
Fast 2 non-consecutive days/week, eat normally the other 5.
Step 2 — Personalise Your Schedule
Your eating window starts from this time
🎯 Your Goal
⏱ Fasting Stages
What Happens Inside Your Body
Live biological stages during your 0-hour fast — each backed by peer-reviewed research.
Last Meal Completed
+0hYour fasting clock starts now. Digestion begins and your body processes the glucose from your last meal.
📄 Mayo ClinicDigestion Phase
+2hBlood glucose peaks and insulin is released. Your body is actively digesting and storing nutrients from the last meal.
📄 NIH — Metabolism OverviewBlood Sugar Stabilizing
+4hInsulin levels begin to drop. Blood sugar returns toward baseline. Your body shifts from storing to maintaining.
📄 PubMed — Insulin & Glucose DynamicsGlycogen Depleting
+8hLiver glycogen stores are running low. Your body begins mobilising free fatty acids as an alternative fuel source.
📄 Cahill GF Jr — NEJM 1970🔥 Ketosis Begins
+12hGlycogen stores are nearly depleted. Your liver starts producing ketone bodies from fat — your brain switches to fat-burning mode.
📄 Cahill GF Jr — NEJM 1970✨ Autophagy Activates
+16hCellular housekeeping begins. Your cells start breaking down damaged proteins and organelles — a key anti-aging mechanism.
📄 Levine & Kroemer — Cell 2008* Biological timelines are approximate and vary by individual. Sources: PubMed, NIH, Cell journal.
How the 5:2 Diet Works
5 Normal Days
Eat your calculated TDEE (Total Daily Energy Expenditure) without restriction. No calorie counting required.
2 Restricted Days
Limit intake to ~500 calories (women) or ~600 calories (men) on 2 non-consecutive days per week (e.g. Monday + Thursday).
The 5:2 diet was popularised by Dr Michael Mosley. A 2021 BMJ systematic review found 5:2 to be comparable in effectiveness to continuous calorie restriction for weight loss.
Medical Disclaimer
This tool provides estimates for informational purposes only. Always consult a licensed healthcare provider before beginning any fasting protocol — especially if you are pregnant, have a history of eating disorders, diabetes, or any other medical condition.
Sources: Mayo Clinic · NIH · PubMed