Bread or Butter
Your fat-vs-carb fuel gauge
Free · In‑App Purchases · Designed for iPhone. Not verified for macOS.
Butter or bread? See what your body is burning.
Bread or Butter turns your live heart rate into a cute, glanceable fuel gauge: a stick of butter (fat) and a French baguette (carbs) meet at a sliding divider that shows your estimated fat-vs-carb mix as you move. Ease off and the butter grows; push harder and the bread takes over.
HOW IT WORKS
• Start a workout in Apple's Workout app, then open Bread or Butter
• It reads your live heart rate and maps your intensity to an estimated fat/carb split using the classic "crossover" curve.
• See your current BPM and heart-rate zone (1–5), based on your heart-rate reserve (Karvonen).
FEATURES
• A playful butter-and-baguette ratio bar with smooth animation
• Heart-rate zones from your resting heart rate and age — read automatically from Health, or set your own in Settings
• Medication offset: if a stimulant raises your heart rate, subtract a few BPM so your zones reflect true effort
• Private by design: everything stays on your Apple Watch. No account, no tracking, no ads.
Bread or Butter is made for curiosity and motivation — not medical use. The fat/carb split and heart-rate zones are ballpark, textbook estimates, not measurements or medical advice.
Connect a Bluetooth heart-rate strap (like a Polar H10) to see your fuel mix live — on your watch or iPhone, no workout needed. The iPhone becomes a live gauge of its own when a strap is connected. Added an optional tip jar, too, if you'd like to say thanks.
The developer, christian Matsoukis, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- christian Matsoukis
- Size
- 2 MB
- Category
- Health & Fitness
- Compatibility
Requires iOS 18.0 or later.
- iPhone
Requires iOS 18.0 or later. - Mac
Requires macOS 15.0 or later and a Mac with Apple M1 chip or later. - Apple Watch
Requires watchOS 26.2 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- In-App Purchases
Yes
- Large Tip $4.99
- Medium Tip $2.99
- Small Tip $0.99
- Copyright
- © 2026 AiVery Systems LLC