Fitzen – AI-Powered Nutrition Tracker

July 27, 2025

Live Demo

Fitzen – AI-Powered Nutrition Tracker

Fitzen is a progressive web app that helps users achieve their fitness goals through strategic nutrition tracking. Whether the goal is fat loss or muscle gain, Fitzen offers a fast, intuitive experience powered by AI and built with cutting-edge web technologies.

Features

  • AI Meal Analysis: Users can upload a photo of their meal, and the AI analyzes it to estimate calories and macros.
  • Personalized Tracking: Users track daily meals, weight, goals, and progress.
  • Dynamic Onboarding Flow: A motivational and reflective questionnaire helps personalize the journey.
  • Multi-language Support: Optimized for Spanish and English speakers.
  • Progressive Web App: Installable and mobile-friendly with offline support.
  • Stripe Payments: Monthly, annual, and lifetime subscription options with checkout page optimizations.
  • Educational Content: In-app guides and AI-generated insights for sustainable fat loss and fitness.

Tech Stack

  • Framework: Next.js 15 with App Router
  • Language: TypeScript
  • Styling: Tailwind CSS, shadcn/ui
  • Backend: Supabase (PostgreSQL, Auth, Storage)
  • AI: OpenAI (via Vercel AI SDK) for and meal image and description analysis
  • Payments: Stripe with secure subscription flows
  • Monitoring: Sentry for error tracking monitoring
  • Deployment: Vercel (optimized for speed and global access)

Key Components

Meal Analyzer

The meal analyzer uses OpenAI's Vision model and structured prompt engineering to return:

  • Calories and macronutrients
  • Food category and portion size
  • Language-aware responses

Smart Onboarding

A 10-question flow captures the user's goals, challenges, lifestyle, and preferences to offer a customized experience and higher conversion into paid plans.

Tracking Dashboard

Clean UI for tracking:

  • Meals by photo or text
  • Weight and goal progress
  • History, trends, and motivational nudges

Development Process

  1. Research: Validated the problem with fitness enthusiasts and nutritionists
  2. MVP Build: Focused on core features — onboarding, tracking, and AI meal input
  3. AI Integration: Used OpenAI and Vercel AI SDK to create intelligent, fast experiences
  4. Monetization: Implemented Stripe for paywall and subscription handling
  5. Marketing Foundation: Built a lean landing page and onboarding flow with conversion in mind

Challenges & Solutions

Challenge: Optimizing AI Cost and Speed

Some requests (e.g. image analysis) were expensive or slow using OpenAI's Vision model.

Solution: Fine-tuned prompts, used streaming responses, and optimized front-end feedback to keep user experience snappy.

Challenge: Balancing Simplicity and Power

Users needed both ease of use and depth of tracking.

Solution: Designed a mobile-first UI with clean flows, optional advanced features, and gamified progress tracking.

Challenge: Trial-to-Paid Conversion

Many users dropped off before subscribing after trying the app.

Solution: Refined onboarding flow, added personalized call-to-action, and introduced email sequences and urgency-driven pricing models.

Future Enhancements

  • [ ] Native app via Expo or Flutter wrapper
  • [ ] Real-time meal database matching
  • [ ] Daily email reminders with AI content
  • [ ] AI-powered coaching insights
  • [ ] Affiliate program with referral tracking

Lessons Learned

  • Shipping > Perfection: Iterating fast while live helped identify blockers early.
  • AI isn't magic: User context and feedback loops make it truly useful.
  • Monetization is a design problem: Pricing, timing, and messaging are just as important as features.
  • Mobile-first is non-negotiable: 90%+ users came from mobile devices — performance and simplicity were critical.

Fitzen represents everything I believe in as a developer: using modern tools, building fast, and solving real problems with thoughtful, lean products. It's more than a side project — it's a mission to help thousands live better through smart nutrition.