SparkFast is an intermittent fasting and prolonged fasting tracker app that helps you monitor your fasting progress, track metabolic health markers like glucose and ketones, follow guided refeed protocols, and achieve your health goals through structured challenges and achievements.
The SPARK chart is a theoretical progress tracker that visualizes the cellular benefits your body experiences during a fast. The name SPARK is an acronym representing five key metabolic stages:
The SPARK chart shows your real-time progress through these phases as your fast progresses, helping you understand the science-backed benefits happening inside your body at each stage.
To start a fast, open the app and tap the "Start Fast" button on the home screen. Choose between intermittent fasting (12:12, 14:10, 16:8, 18:6, 20:4, OMAD) or prolonged fasting (36h, 48h, 72h, 96h), or create a custom fast with your preferred duration.
SparkFast offers a 7-day free trial so you can explore all features before committing. After the trial, you can continue with a monthly or yearly subscription plan. You can also apply a promo code during signup for special access.
SparkFast supports all popular intermittent fasting schedules including 12:12, 16:8, 18:6, 20:4, and 23:1 (OMAD). You can also create a custom intermittent fasting schedule with your own eating window times.
Prolonged fasting is any fast lasting longer than 24 hours. SparkFast supports prolonged fasts including The Autophagy Spark (36h), Peak Repair (48h), The Regenerator (72h), and Sustained Renewal (96h). You can also set a custom duration for fasts of any length.
The SPARK phases represent the cellular repair stages your body goes through during a fast. SparkFast tracks your real-time progress through these phases, showing when your body enters fat burning, ketosis, autophagy, and deep cellular renewal.
A refeed protocol is a structured eating plan that guides you on what to eat and when after completing a prolonged fast. SparkFast provides default refeed protocols for 36h, 48h, 72h, and 96h fasts with step-by-step instructions to safely reintroduce food and avoid digestive discomfort.
Yes, you can create custom refeed templates in SparkFast. Tap the "Customize This Protocol" button to copy any default protocol and modify the food items, timing, and sequence to match your dietary preferences.
SparkFast lets you track blood glucose and ketone readings by hand or automatically from a Keto-Mojo meter. Tap the Glucose or Ketones tile on your dashboard, then the + button, to log a reading. To sync a meter, go to Settings > Data > Keto-Mojo. Your Keto ratio (Dr. Boz or GKI) updates as soon as you have a paired glucose and ketone reading.
GKI (Glucose Ketone Index) is a ratio that measures your metabolic health by dividing your glucose level by your ketone level. SparkFast automatically calculates your GKI when you have paired glucose and ketone readings taken within a 15-minute window, and displays your metabolic zone.
The Dr. Boz Ratio is a metabolic health metric created by https://bozmd.com/ — a board-certified internal medicine physician, bestselling author of Anyway You Can and Keto Continuum, and a leading expert in ketogenic nutrition and metabolic health. Dr. Bosworth developed this simplified ratio to help patients monitor their metabolic state without complex math.
The formula is: Blood Glucose (mg/dL) ÷ Blood Ketones (mmol/L). Unlike the GKI which requires converting glucose units first, Dr. Bosworth intentionally skipped this conversion step to make the calculation more user-friendly and less prone to error.
SparkFast automatically calculates your Dr. Boz Ratio when you have paired glucose and ketone readings, and displays your metabolic zone:
You can choose between GKI or Dr. Boz Ratio as your preferred metabolic display in Settings.
You can track your weight by entering readings by hand or by syncing automatically from Apple Health (iOS) or Health Connect (Android). Tap the Weight tile on your dashboard to log a reading and to see your weight history chart, BMI, and progress toward your goal weight. Set your goal weight in Settings > Profile.
Yes, SparkFast includes a hydration tracker to log your daily water intake. You can customize your glass size, set a daily water goal, and enable hydration reminders at your preferred frequency during fasting.
Yes. SparkFast reads sleep duration and stages (light, deep, REM) from Apple Health on iOS or Health Connect on Android, and shows how your sleep correlates with your fasting. Sleep data needs a source that writes to your health app — an Apple Watch, a band, or a sleep app. Without one, you can log sleep by hand from the Sleep tile on your dashboard.
Yes. SparkFast integrates with Apple Health on iOS to sync weight, steps, and sleep automatically. Go to Settings > Data > Apple Health and tap Connect. The page shows what syncs and where each type comes from — for example, steps come from your iPhone with no watch needed, while sleep needs an Apple Watch or a sleep app.
Yes. On Android, SparkFast integrates with Health Connect — Google's health data hub, which replaced Google Fit — to sync weight, steps, and sleep automatically. Fitbit, Samsung Health, Garmin and other apps write into Health Connect. Go to Settings > Data > Health Connect and tap Connect. If Health Connect is not installed, the app will prompt you to install it from the Play Store.
Go to Settings > Data > Keto-Mojo and tap Connect. Select your region (US, EU, or Canada) and sign in with your MyMojoHealth account. SparkFast then syncs your glucose and ketone readings automatically; "Sync now" on the same page pulls the last 90 days on demand.
SparkFast sends fasting milestone notifications (at 12h, 18h, 24h, 36h, 48h, 72h), hydration reminders, electrolyte reminders, eating window alerts, refeed step reminders, challenge milestone updates, and motivational messages.
SparkFast sends three eating window notifications: one hour before your eating window opens, when your eating window begins, and one hour before your eating window closes. These help you stay on schedule with your intermittent fasting plan.
Not yet. SparkFast does not offer a quiet-hours setting in the app. To silence notifications overnight, use your phone's Do Not Disturb or Focus mode, or turn off Push notifications in Settings > Notifications & Reminders.
Go to Settings > Notifications & reminders. Turn on Hydration reminders, then set how often you want them (every 30 minutes to every 6 hours) and the time window they are active. The line under the card tells you how many reminders that makes per day. Electrolyte reminders are on the same screen: add as many daily times as you like, and tap a time to change it.
Fasting challenges are structured programs that help you build consistent fasting habits. SparkFast offers 25+ challenges across beginner, intermediate, and advanced levels, including day-based consistency challenges and single prolonged fast challenges.
SparkFast awards achievement badges when you reach fasting milestones. Badges range from Bronze to Diamond rarity and include achievements like First Steps (first 24h fast), Week Warrior (7-day streak), and Thousand Hour Hero (1000 total fasting hours).
SparkFast supports kilograms or pounds for weight, millilitres or ounces for hydration, mg/dL or mmol/L for glucose and for ketones, and Dr. Boz or GKI for your Keto ratio. Change any of them in Settings > Units — each is a one-tap toggle.
SparkFast supports sign-in with email/password, Google and Apple. You can create an account or sign in from the welcome screen.
Open Settings and scroll to the bottom. Tap Delete account and confirm. This permanently removes your account and all of your data.
If your fasting timer is not displaying, ensure you have an active fast running. Check the home screen for the "Start Fast" button. If the issue persists, try closing and reopening the app.
Open Settings > Data and tap the integration (Apple Health, Health Connect, or Keto-Mojo). The page shows whether it is connected and what it syncs. If it says Not connected, tap Connect and grant the permissions your phone asks for. If it is connected but a type shows no data, that type has no source yet — for example, sleep needs an Apple Watch, a band, or a sleep app. You can also log any reading by hand from its tile on the dashboard.
Check Settings > Notifications & reminders: Push notifications must be on, and the reminder you expect (hydration, electrolytes, refeed) must be switched on below it. Then check your phone's notification settings for SparkFast, and that Do Not Disturb or a Focus mode is not active.
Open a refeed protocol and tap the ? icon in the top-right corner. The guided tour plays again and shows you how to select protocols, manage templates, and customise your refeed plan.
SparkFast provides educational content about fasting but is not a substitute for professional medical advice. Always consult with a healthcare provider before starting a fasting regimen, especially if you have underlying health conditions.
SparkFast uses Firebase security with encrypted data storage, App Check for bot protection, and follows GDPR compliance practices. Your email is never logged to crash reporting services, and all health data stays secure in your private account.
We love hearing from our users! If you have ideas for new features or improvements, please email us at support@sparkfast.app with "Feature Request" in the subject line.
Email: support@sparkfast.app
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