Comparison

Sardines Fasting vs FastJoy

Price, ratings, monetisation and update history for both apps, side by side โ€” with what reviewers say about each.

Head to head
About

Sardines Fasting

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SardinesFasting guides you through structured sardine fasts โ€” 24 hours to 21 days where you eat only sardines, water, coffee or tea. Protein and omega-3 preserve lean mass while insulin stays low enough to trigger autophagy. WHY SARDINES, NOT WATER A water-only fast eventually burns muscle. Sardines are 22-25 g of protein and 1.5 g of EPA/DHA omega-3 per can, low in mercury, calcium-rich (bone-in). You get the metabolic switch, ketosis and autophagy of a water fast โ€” without the lean-mass cost. FIVE BUILT-IN PROTOCOLS โ€ข 24h Sardine Reset โ€” beginner, one-day metabolic switch โ€ข 3-Day Insulin Reset โ€” intermediate, crushes insulin, surges ketones โ€ข 5-Day Repair โ€” advanced, deeper autophagy and stem-cell signaling โ€ข 21-Day Advanced N=1 โ€” extended self-experiment (medical supervision required) โ€ข 17h Hybrid IF โ€” sustainable daily protocol LIVE TRACKING โ€ข Hour-by-hour fasting timer that shows your active phase: digestion โ†’ glycogen depletion โ†’ metabolic switch โ†’ ketosis โ†’ autophagy โ†’ deep repair โ†’ stem-cell window โ€ข Manual or CGM/CKM logging of glucose and ketones (SiBio, NutriSense, HealthKit) โ€ข Automatic Glucose-Ketone Ratio (GK Ratio) and GKI calculator โ€ข Visceral-fat and waist tracking โ€ข Streak, autophagy-days-this-month, sleep, mood BUILT ON PEER-REVIEWED SCIENCE 35+ scientific references across autophagy (Takeshige 1992, Mizushima 2007), intermittent fasting (de Cabo & Mattson NEJM 2019, Longo 2014), ketosis (Newman & Verdin 2017, Veech 2004), omega-3 nutrition (Mozaffarian JAMA 2006), insulin resistance reversal (Hallberg 2018), and prolonged-fasting stem-cell biology (Cheng 2014). Every claim links to a paper you can verify. CYCLE-AWARE FOR WOMEN Long fasts in the luteal phase backfire. The onboarding asks about your cycle and concentrates deeper protocols in the follicular phase. COMMUNITY Share your progress, join structured group challenges (3-Day Insulin Reset, Sardine September, cycle-aware fasting), see a weekly leaderboard ranked by autophagy hours. Posts are moderated. SAFETY FIRST Risk-assessment questionnaire flags contraindications (pregnancy, eating-disorder history, diabetes medication, low BMI). Explicit watch-outs for refeeding syndrome on extended fasts. LOCAL-FIRST PRIVACY Logs stay on your phone. No account required. Optional HealthKit sync. The AI coach (Pro) processes your data in-memory and discards it. 36 LANGUAGES Full UI translation across 36 languages โ€” metabolic health shouldn't be paywalled behind English. PRO โ‚ฌ4.99/month or โ‚ฌ49/year, billed automatically. Pro adds: AI coach with cycle-aware adjustments, automatic CGM/CKM sync, hour-by-hour autophagy phase tracking, doctor-ready PDF reports. Cancel anytime in Settings โ†’ Apple ID โ†’ Subscriptions. Not medical advice. Talk to your doctor before any extended fast. Terms of Use (EULA): https://sardinesfasting.com/legal/terms/

About

FastJoy

Features
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FastJoy is the simple, private way to track intermittent fasting. Pick a protocol, start the timer, and watch your fasting and eating windows in real time โ€” no account, no paywall on the core timer, and everything stays on your device. WHY FASTWINDOW - Beautiful animated fasting timer with live elapsed time and progress ring - Choose 16:8, 18:6, 20:4, OMAD or a custom fasting window - Informational fasting stages as the hours add up (fat burning, ketosis, autophagy zone) - Current streak, today's eating window and target end time at a glance - Edit your start time anytime โ€” perfect when you forget to hit start TRACK EVERYTHING - Full history of every fast with met-goal status - GitHub-style consistency heatmap of your fasting days - Weekly fasting hours and calendar overview STATS & PROGRESS - Average fast length, longest fast, completion rate and streaks - Fast-duration trend chart and this-week-vs-last comparison - Patterns by weekday and start time of day - Optional weight log with a clean trend chart - Dozens of achievements to keep you motivated REMINDERS THAT HELP - Get notified the moment your fasting goal is reached - Optional "time to start fasting" and hydration reminders - 100% local notifications โ€” no servers, no tracking of your habits PRIVATE BY DESIGN - No sign-up, works fully offline - Optional Face ID / Touch ID lock - Export and import your data as JSON anytime - Available in English, Spanish, French, Italian, German and Portuguese FastJoy is a tracking aid only and does not provide medical or nutritional advice. Intermittent fasting is not suitable for everyone, including during pregnancy or with certain medical conditions. Consult a qualified healthcare professional before changing your eating patterns. Start your first fast today and build a routine that lasts.

Screenshots

Sardines Fasting4 screens
FastJoy4 screens

Verdict

The call

The clearest difference is in-app purchases: FastJoy at none against Sardines Fasting's 2. FastJoy also leads on device support (3 vs 1) and iOS requirement (13.0 vs 17.0). Sardines Fasting's advantage is ads (none vs shown). On price there is nothing between them.

Scored on Price ยท Rating ยท Positive reviews ยท Number of ratings ยท Update frequency ยท Ads ยท In-app purchases ยท Monetization ยท Best chart rank ยท Devices ยท Requires iOS

CostPrice ยท In-app purchases ยท Ads ยท Monetization

Both are free to download. Sardines Fasting sells 2 in-app purchases, starting at $4.99 per month. FastJoy asks for nothing beyond the download.

Scorecard4 real differences ยท 2 level
Sardines Fasting versus FastJoy: the parameters behind the verdict, then further details
ParameterSardines FastingFastJoy
PriceFreeFree
Update frequencyEvery 4 daysโ€”
AdsNo โ€” betterYes
In-app purchasesYesNo โ€” better
DevicesiPhoneiPhone, iPad, iPod โ€” better
Requires iOS17.013.0 โ€” better
Further details โ€” not scored
Size5 MB41 MB
Age rating17+12+
DeveloperStephane SprauerFerran Espuna

In-app purchases

2 purchases

Sardines Fasting

Subscriptions2
  • SardinesFasting Pro โ€” Monthly$4.991 Month
  • SardinesFasting Pro โ€” Annual$49.991 Year
None

FastJoy

No in-app purchases

Questions

Is Sardines Fasting free?
Sardines Fasting is free to download, with in-app purchases available.
Is FastJoy free?
FastJoy is free to download, with no in-app purchases.
Do Sardines Fasting or FastJoy have ads?
FastJoy shows ads; Sardines Fasting does not.

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