Turning it on
Enable Health sync in your Profile — Apple Health on iPhone, Health Connect on Android. The toggle is always there; if Health Connect isn't installed, tapping it points you to the Play Store. If you declined a permission earlier, your phone's Settings is where it gets re-granted; the app points you there.
What syncs in
Every sync reads weight and body-fat percentage from your health app. Height is read too, but only when you first connect and during setup — not on every sync. That includes measurements other sources put there — a smart scale that writes to Apple Health lands in your Macros weight history automatically, feeding your trend and expenditure like any weigh-in.
Entries that originated in Gravl apps are recognized and skipped on import, so nothing ever counts twice.
What syncs out
Weights, height, and body fat you log in Macros are written back to your health app — and so is your food diary's nutrition: each logged entry exports its calories and a broad breakdown (protein, carbs, fat, fiber, sugar, sodium, and more), so other health apps can see your nutrition. Deleting a weigh-in in Macros also removes the entry it had written to your health app; entries you created elsewhere are never touched.
What it never reads
Health sync never reads workouts, active energy, sleep, or heart rate — none of it, on either platform. Your expenditure comes from your own logging and weight trend, not from a wearable's activity estimate. See does my watch's calorie burn count?.
Two things are read once, at setup, and never again: your average daily step count and, on iPhone, your date of birth. During onboarding the app can offer to read your step count to suggest your activity level — the trailing 30 days, ignoring any day under 500 steps as "phone left behind", and only if at least 7 days qualify. Your date of birth simply prefills your profile. Neither is read by ongoing sync, and no step data ever reaches the adaptive estimate.
On Android, the Health Connect permission sheet includes Steps when you connect, even though they are only read during setup.
Nutrition is one-way out: food logged directly in other apps isn't imported, from your health app or anywhere else. To bring a history across from another tracker, see import your data.
When it syncs
Syncing runs when you open or return to the app, not continuously in the background, and at most once every fifteen minutes — if a scale reading seems missing, come back to Macros a little later and it will be there.