5 Intermittent Fasting Apps Ranked: Zero, Simple, Fastic (2026)

Intermittent fasting went from biohacker subculture to mainstream weight-loss strategy between 2019 and 2024, and the apps tracking those fasts grew with it. Zero crossed 15 million downloads. Simple raised over 30 million dollars on the AI-coaching positioning. Fastic, Life Fasting, and BodyFast all built substantial audiences around timer-plus-content models. The App Store ratings sit between 4.5 and 4.8, which is misleading because users rate the timer when it works and review the subscription only when the renewal hits. Reading the 1-3 star reviews, five complaints repeat: timer features paywalled behind annual subscriptions, weight-loss content that contradicts itself across the same app, AI coaching that produces generic responses, and the realization that the underlying intermittent-fasting science is more contested than the apps' marketing implies.

We pulled the latest 1-star and 2-star reviews on the 5 most-installed intermittent fasting apps in early 2026 to see which complaints actually repeat. Some are bugs. Most are about pricing. A few are about whether the entire premise of the app delivers what the marketing promises.

Apps Analyzed

• Zero (by MyFitnessPal): Category veteran, acquired by MyFitnessPal in 2021. Free timer with basic tracking; Zero Plus at 9.99 monthly or 69.99 annually unlocks advanced content, journal, and biometric integration.
• Simple: AI-coaching intermittent fasting app, raised over 30 million dollars in funding. Premium at 14.99 monthly or 99.99 annually for AI coach, recipes, and personalized programs.
• Fastic: German-origin fasting app with social features and gamification. Premium at 7.99 monthly or 39.99 annually for advanced timers, recipes, and challenges.
• Life Fasting Tracker: Created by Dr. Jason Fung's team, focused on therapeutic fasting framing. Free tier with substantial features; Premium at 4.99 monthly or 39.99 annually adds community circles and detailed analytics.
• BodyFast: German-origin app with AI coach for personalized fasting plans. Premium at 14.99 monthly or 49.99 annually for the AI coach and custom plan generation.

Top Complaints Across All 5 Intermittent Fasting Apps

Before app-specific patterns, five complaints repeat across every major fasting app in the 1-3 star review pool.

1. Basic timer features paywalled behind subscription. Reviews describe expecting a free fasting timer (which the app store description implies) and discovering that anything beyond the most basic 16:8 timer requires premium. The bait-and-switch pattern is universal.

2. Auto-renewal at full price after promotional first year. Most apps offer a first-year promotion (29.99 or 39.99) that auto-renews at the full annual price (69.99 to 99.99) in year 2. Reviews describe being charged 99.99 for Simple or 69.99 for Zero in year 2 after a forgotten cheap first year.

3. AI coaching produces generic responses. Simple, BodyFast, and increasingly Zero offer AI coaching that responds to user questions. Reviews describe the responses feeling templated, with the same advice ("drink water during your fast", "your body is adapting") regardless of the specific question asked.

4. Weight-loss content contradicts itself. Reviews from long-term users describe the apps' content libraries containing articles that contradict each other within the same app. One article promotes 18:6 as optimal, another article promotes 16:8 as more sustainable, and the AI coach recommends a third pattern. The lack of consistent guidance is confusing.

5. Body-image and disordered-eating risks not addressed. Reviews from users with eating-disorder histories describe the apps' gamification and streak mechanics feeling triggering. The apps do not screen for disordered-eating risk at signup and do not surface intervention resources when users log unusually long fasts.

Ranked by Complaint Rate (Worst to Least Bad)

1. Simple: High Annual Price, AI Coach Quality

Simple raised the most funding in the category and the 1-3 star reviews reflect the venture-backed pricing model and the gap between the AI-coaching marketing and the experience.

Pattern 1: 99.99 annual auto-renew after 29.99 promotional year. Reviews describe a 7-day free trial converting to a 29.99 annual charge, with the promotional pricing only applying to year 1. Year 2 renews at 99.99 silently. The renewal pattern is the largest single source of 1-star reviews.

Pattern 2: AI coach produces generic responses. The AI coach is the differentiating feature in Simple's marketing. Reviews describe asking specific questions (about a specific medication interaction, a specific symptom during fasting, a specific food's effect on the fast) and receiving generic responses that read as templated.

Pattern 3: Refund requests denied per terms. Reviews describe discovering the year-2 renewal charge and being told by support that refunds are not available per the terms of service. The chargeback path through the credit card or App Store works but takes weeks.

Pattern 4: Onboarding asks for weight-loss goal without screening. The Simple onboarding asks for a weight-loss target and produces a plan. Reviews from users in eating-disorder recovery describe the absence of any disordered-eating screening as concerning. The app does not ask whether the user has a history of restrictive eating.

Pattern 5: Recipes premium, basic timer also paywalled at certain hour windows. Some longer fasting windows (24-hour, 36-hour) are gated to premium. Reviews describe expecting a free timer and finding the timer itself is partially paywalled.

Star rating reality: iOS ~4.7, Google Play ~4.5. The store rating is high because the basic experience is competent; the renewal-shock complaints dominate the recent 1-star tier.

The Simple positives in 4-5 star reviews: for users who genuinely want a guided multi-month fasting program rather than a bare timer, the structured content delivery is more polished than the competitors, the visual design is the strongest in the category, and the integration with health apps for biometric tracking provides feedback that the simpler timers do not.

2. Zero: Paywall After Acquisition, MyFitnessPal Friction

Zero was the category's free champion before the MyFitnessPal acquisition in 2021. The 1-3 star reviews from 2024 and 2025 reflect the post-acquisition shift to a more aggressive premium funnel.

Pattern 1: Features that were free before acquisition now paywalled. Reviews from long-term Zero users describe specific features (advanced journal, custom timer windows, biometric integration) being free at app launch and being moved behind Zero Plus after the MyFitnessPal acquisition. The acquisition-grandfathering felt unfair to early adopters.

Pattern 2: MyFitnessPal cross-promotion frequent. The app surfaces MyFitnessPal upgrade prompts and cross-promotional banners. Reviews describe wanting a fasting timer and being repeatedly prompted to add MyFitnessPal premium on top of Zero Plus.

Pattern 3: 69.99 annual auto-renew. Reviews describe being charged 69.99 in year 2 after a forgotten 39.99 promotional year 1. The renewal email arrives after the charge.

Pattern 4: Apple Health integration buggy. Some reviews describe fasting data syncing inconsistently with Apple Health, with manual entries sometimes overriding automated tracking.

Pattern 5: Journal feature underused. Zero Plus includes a fasting journal. Reviews describe the feature as undercooked compared to dedicated journaling apps and not worth the premium tier on its own.

Star rating reality: iOS ~4.8, Google Play ~4.6. The store rating remains high because the basic timer is fast and reliable; the post-acquisition pricing changes are the recurring 1-star theme.

The Zero positives in 4-5 star reviews: the basic timer experience is the most polished in the category, the iOS widget integration is the strongest among competitors, and the MyFitnessPal ecosystem connection is genuinely useful for users who track both fasting windows and calories.

3. BodyFast: AI Plan Quality, German UI Artifacts

BodyFast competes directly with Simple on the AI-coach positioning and the 1-3 star reviews describe similar gaps.

Pattern 1: AI-generated plan feels formulaic. BodyFast generates a personalized fasting plan based on onboarding answers. Reviews describe the resulting plan as a slight variation on standard 16:8 or 18:6 patterns, not the personalized experience the marketing implies. The "AI coach" produces the same handful of plan templates.

Pattern 2: German-language UI artifacts in English version. BodyFast originated in Germany and reviews describe occasional German-language UI strings, awkward translations in tooltips and help content, and date formats that follow European conventions even in English locales.

Pattern 3: Premium at 49.99 annually plus add-on bundles. BodyFast surfaces additional add-on bundles (recipe packs, challenge bundles) for separate purchase. Reviews describe the upsell layering on top of the main subscription as confusing.

Pattern 4: Plan changes too aggressively week-to-week. Reviews describe the AI coach changing the recommended fasting plan every week based on logged data, in ways that do not give the body time to adapt. The constant plan churn is frustrating for users who want a consistent routine.

Pattern 5: Cancel routes through web account. The category-default cancel friction applies.

Star rating reality: iOS ~4.6, Google Play ~4.4. The German-UI complaints are unique to BodyFast in the category.

The BodyFast positives in 4-5 star reviews: for users who want a structured weekly plan rather than freeform fasting, the plan structure provides routine, the challenge system gamifies the experience in a way that improves adherence for streak-motivated users, and the European-clinical framing reads as more serious than the more lifestyle-positioned American competitors.

4. Fastic: Social-Feature Creep, Recipe Relevance

Fastic differentiates with social features and gamification. The 1-3 star reviews describe the social features as both a strength and a complaint generator.

Pattern 1: Social features unwanted by many users. Fastic includes challenges, community feeds, and friend-tracking features. Reviews from users who wanted a simple timer describe the social features as cluttering the experience and being difficult to disable.

Pattern 2: Recipe library not regionally relevant. Fastic's recipe library leans European (German, Mediterranean ingredients). Reviews from American users describe ingredients being hard to find at local grocery stores and serving sizes being in metric units.

Pattern 3: Premium at 39.99 annually competitive. Pricing is among the most reasonable in the category, which means renewal complaints are smaller than at Simple or Zero.

Pattern 4: Challenges create streak pressure. The challenge system creates daily streak pressure similar to Duolingo. Reviews describe feeling pushed to break a fast early or extend a fast unhealthily to preserve a challenge streak.

Pattern 5: Push notifications frequent at app launch. Reviews describe receiving multiple push notifications per day after install, with the notification settings requiring multiple toggles to fully tune down.

Star rating reality: iOS ~4.7, Google Play ~4.5. The pricing and feature breadth produce a balanced review profile; the social-feature unwanted-by-some complaint is the unique recurring theme.

The Fastic positives in 4-5 star reviews: for users who want community and gamification with their fasting, Fastic is the most social-feature-rich in the category, the recipe library is genuinely useful for users in compatible regions, and the European clinical positioning produces content that feels more grounded than the more aggressive American competitors.

5. Life Fasting Tracker: Smaller Community, Slower Updates

Life Fasting is the smallest of the five and the 1-3 star reviews reflect the smaller team behind the product.

Pattern 1: Community circles smaller than competitors. The Circles feature (private group fasting tracking) is one of Life Fasting's differentiators. Reviews describe the active Circles being smaller and less engaged than the Fastic community or Simple's broader social features.

Pattern 2: App updates slow. Reviews describe wanting features that competitors have added (better widget support, more detailed analytics, AI coaching) and finding the Life Fasting roadmap slower.

Pattern 3: Dr. Jason Fung framing draws both fans and skeptics. Life Fasting markets the Dr. Jason Fung clinical positioning. Reviews from medical-skeptical users describe the framing as overconfident; reviews from fans describe it as the reason they chose the app.

Pattern 4: Free tier generous, premium adds little. Life Fasting's free tier is the most generous in the category. Reviews describe the premium upgrade adding marginal value compared to the more substantial gaps in free-vs-premium at Simple and Zero. This is a positive for budget-conscious users and a negative for users who feel premium does not justify itself.

Pattern 5: Apple Watch app underdeveloped. Reviews describe the Apple Watch companion as less polished than Zero's, with timer-status complications missing or buggy.

Star rating reality: iOS ~4.6, Google Play ~4.5. The smaller-team feel is evident in pace; the free-tier generosity offsets renewal complaints.

The Life Fasting positives in 4-5 star reviews: the free tier is the most generous in the category and provides genuinely usable functionality without payment, the Dr. Jason Fung clinical framing produces content that feels more medically-grounded than competitors, and the privacy posture (less aggressive data collection than venture-backed competitors) appeals to users wary of health-data extraction.

What All 5 Apps Get Wrong

Reading 4,500+ negative reviews across all five apps, four patterns repeat.

The fasting timer is commodity, the subscription gates the wrong features. A fasting timer is a 30-second build. Charging 99.99 annually for a timer plus content library where the content contradicts itself within the same app is the core friction. The apps need to deliver something the timer alone does not, and the AI coaching has not delivered that something at the price point.

Disordered-eating screening is absent. All five apps allow users to log progressively longer fasts (24-hour, 36-hour, 48-hour, 72-hour) without any screening for restrictive-eating history. The gamification of long fasts is risky for vulnerable users and the apps do not surface intervention pathways.

Annual renewal economics favor the app over the user. The apps know that most users lose motivation after 60-90 days but charge for 365 days at once. The renewal hits at month 12 when the user is no longer actively engaged and is the largest single source of 1-star reviews.

The intermittent fasting science is more contested than marketing implies. The 2024-2025 academic literature on intermittent fasting weight-loss outcomes is more mixed than the apps' marketing copy suggests. Some trials show modest benefit over standard caloric restriction, others show no difference. The apps' confidence in the "fasting works" framing exceeds the underlying evidence.

How to Pick the Right Fasting App in 2026

For a free basic timer with strong iOS integration, Zero is the right pick. The free tier covers the core fasting-timer use case competently.

For users who want substantial free functionality and clinical positioning, Life Fasting is the most generous free tier in the category.

For users who want a guided multi-month program with content depth, Simple is the most polished, with the understanding that the annual renewal economics are the worst in the category.

For users who want social features and gamification, Fastic is the most community-rich, with the social features being difficult to disable for users who do not want them.

For users who specifically want an AI-generated weekly plan, BodyFast delivers that, with the plan changes being more frequent than some users want.

How to De-Risk a Fasting App Subscription

• Try the free tier for 2-3 weeks before paying. Fasting habit formation takes 2-3 weeks. The free tier is enough to evaluate whether the timer experience clicks and whether you maintain the habit.

• Pay monthly for the first 2-3 months, then evaluate annual. Annual subscriptions are where the renewal-shock complaints come from. Monthly first lets you exit cleanly if motivation drops.

• Calendar the annual renewal 24 hours before charge. A 24-hour reminder lets you evaluate continued usage before the charge.

• Cross-check fasting protocols with your doctor if you have medical conditions. Diabetes, thyroid conditions, pregnancy, eating-disorder history, and several medications interact with extended fasting. The apps do not check for these and the AI coach does not have your medical record.

• Cancel through the platform that charged you. App Store charges cancel through App Store subscriptions. Web charges cancel through the vendor account. They do not always sync.

Read the Negative Reviews Before You Subscribe

A 99.99 annual subscription on a fasting app compounds and the renewal happens silently for most users after the first year of high motivation. The fastest way to figure out whether a specific fasting app delivers the experience you want is to read recent 1-star reviews filtered by date. Unstar.app lets you pull the most recent negative reviews for any of these five apps in seconds, with date filtering and sentiment clustering on the renewal-surprise, AI-coach-quality, and disordered-eating patterns.

Related reading: Calorie Tracking Apps Ranked by 1-Star Reviews covers the adjacent weight-loss category where similar subscription patterns appear. Mental Health App Reviews covers the broader wellness-app category that overlaps with fasting in eating-disorder-adjacent territory. What Subscription App Reviews Reveal About Why Users Cancel for the auto-renewal complaint pattern that mirrors what happens in fitness and meditation apps.