Bread or Butter

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.